Class 12 Engineering Chemistry - General Principles And Processes Of Isolation Of Elements

Which type of ore is concentrated by froth floatation process?

Sulphide ores are concentrated by froth- flotation process. Only sulphide ores are concentrated by this method because pine oil selectively wets the sulphide ore and hence brings it to the froth.

Why is pine oil used in froth floatation method?

1) pine oil consists mainly of cyclic terpene alcohols.

2)pine oil is used in froth flotation process because it does not have affinity towards water (because of the hydrophobic chemicals as its constituents)and it attracts impurities which can be washed away.

In Hall-Heroult process $$CO_2$$ is released at ?

The Hall Heroult process is the major industrial process for smelting aluminium. The aluminium reduction process is described as,

$$2Al_2O_3+3C\longrightarrow 4Al+3CO_2$$

Anode reaction $$C_{(s)}+20^{2-}_{(l)}\longrightarrow {CO_2}_{(g)}+{4e^-}$$

Cathode reaction $$Al^{3+}_{(l)}+3e^-\longrightarrow Al_{(l)}$$

So, we can see that $$CO_2$$ is released at anode.

Why are copper and aluminium are used to make electric wires?

Copper and aluminum are used to make electric wire because both are good conductor of electricity heat which are chop in prices well as better than other metals most probably Immunol are less expensive than other metal used in electricity wire

Name the compound of nitrogen occur in earth crust ?

Nitrogen is a fairly common element in the Earth's crust. It occurs primarily as nitrates and nitrites. Nitrogen is by far the most important element in the Earth's atmosphere. It makes up 78.084 percent of the atmosphere.

Draw labelled diagram of Zone refining process. In which this process is useful?

The labelled diagram of Zone refining process is as shown. It is useful to obtain ultra pure metals and non-metals. In this process 99.999 % purity is achieved. Silicon, germanium and gallium are refined by this method.

How are lanthanides extracted from monazite sand?

The method used for the extraction of lanthanides from monazite sand consists of the steps which have been shown in flowsheet.
Individual lanthanides are separated by a suitable physical method. The anhydrous fluorides and chlorides are heated under argon atmosphere in presence of calcium at $$1270$$ $$K$$ to get the individual metal. The pure metal is obtained by heating the trifluorides of lanthanides in the presence of calcium and lithium.

Give the importance uses of copper.

All US coins are now copper alloys, and gun metals also contain copper. Mostcopper is used in electrical equipment such as wiring and motors. This is because it conducts both heat and electricity very well, and can be drawn into wires.

Identify the pairs of metals and their ores from the folllowing

The chief ore of aluminium is bauxite.

The chief ore of mercury is cinnabar.

The chief ore of tin is cassiterite.

What is amalgam ?

It is a special class of alloy in which one of the component of alloy is mercury (Hg). Example, Zinc Amalgam (Zn-Hg).

What are the uses of copper?

All US coins are now copper alloys, and gun metals also contain copper. Most copper is used in electrical equipment such as wiring and motors. This is because it conducts both heat and electricity very well, and can be drawn into wires.

Name two metals which are purified by distillation method.

Refining of volatile metals like mercury, zinc, etc. is done by distillation. The impure form of these metals can be distilled to get their vapours, which are then condensed to get the pure metal.

Match Column-I with Column-II.

Calcium (Ca) is found as carbonates, $$CaCO_3$$.

Zinc(Zn) is found as its sulphide$$ZnS$$, carbonate $$ZnCO_3$$ and oxide $$ZnO$$.

Chrominum(Cr) is found as its oxide $$Cr_2O_3$$.

Silver (Ag) is found in its native state i.e. $$Ag$$.

A mineral is rich in ZnS and PbS. If it can be concentrate by froth flotation process enter 1 else 0.

NaCN is added benefication by froth floation process (FFP), ZnS in convered to soluble complex $$Na_2[Zn(CN)_4]$$ and PbS goes into froth by FFP.

Explain froth flotation process of copper pyrites.

Copper is extracted from copper pyrites by froth flotation process.

Froth flotation method is used to separate particles based on the differences in the ability of air bubbles to selectively attach to specific mineral surfaces in a mineral-water slurry. A finely crushed ore is suspended in water and a blast of air is passed through the suspension. The wet particles to which air bubbles are attached float as a froth which is skimmed, whereas the particles to which air bubbles are not attached gets heavy and sink to the bottom.

Copper is extracted from its principle ore Copper pyrites $$CuFeS_2$$. The ore is concentrated by froth flotation process. The concentrated ore is then roasted in a furnace where reactions remove sulphur and Arsenic gases-

$$S+O_2 \rightarrow SO_2$$ and $$4As+3O_2$$$$\longrightarrow$$$$2As_2O_3$$

And then the copper pyrite gets converted to a mixture of $$Cu_2S$$ and $$FeS$$ by the following reactions.

$$2CuFeS_2 + O_2 $$ $$\longrightarrow$$ $$Cu_2S+2FeS+SO_2$$

These Sulphides are then oxidized and by smelting them, copper is extracted successfully.

Sulphide ore is concentrated by the method:
Froth flotation process
Magnetic separation
Gravity method
Calcination method

Froth Floatation method
This method is mainly employed for the concentration of sulphide ores. The method is based on the different wetting characteristics of the gangue and the sulphide ore with water and oil. The gangue preferrentially wetted by water and the ore by oil. The crushed ore along with water is taken in a floatation cell. Various substances are added depending on the nature of the ore and a current of air is blown in.

Sulphide ore is common for _______ metal. (Cu, Mg, Na, K)
Choose the correct one.

Argentite ($$Ag_2S$$)
Galena ($$PbS$$)
Chalcocite ($$Cu_2S$$)
Copper pyrite (chalco pyrite) [$$CuFeS_2$$]

∴ Cu is the correct answer.

Based on the above Ellingham diagram, the formation of carbon monoxide from carbon can reduce the metal oxide to metal at a temperature _______ the point of intersection of the two lines.
1. Equal to
Higher than
Lower than
None

To occur reaction,
$$\Delta\,G\, =\, - ve, \,T\,\Delta\,S\,>\, \Delta\,H$$

Since, $$\Delta\,G\, =\, \Delta\,H\, -\, T\,\Delta\,S$$

So, temperature should be higher than the point of intersection of the two lines.

Among the methods for extracting metals from their ores, i.e.,roasting a metal sulphide,chemical reduction of a metal oxide, andelectrolysis, the preferred method depends on $$E^{\circ}$$ value for the reducing half-reaction:
$$M^{n+}{(aq)}\, +\, ne^{-}\, \rightarrow\, M(s)$$
Which method is preferred for the metals with the most negative $$E^{\circ}$$ values?

If $$E^o$$ is most negative for a metal than it will have the highest tendency to reduce and we will use electrolysis method to extract metal from its ore.

The methods for extracting metals from their ores are:
roasting a metal sulphide
chemical reduction of a metal oxide
electrolysis,
The preferred method depends on $$E^{\circ}$$ value for the reducing half-reaction:
$$M^{n+}{(aq)}\, +\, ne^{-}\, \rightarrow\, M(s)$$
Which method is preferred for the metals with the most positive $$E^{\circ}$$ values?

Roasting is a step of the processing of certain ores.
Roasting is a metallurgical process involving gassolid reactions at elevated temperatures with the goal of purifying the metal component(s). Often before roasting, the ore has already been partially purified, e.g. by froth floatation. The concentrate is mixed with other materials to facilitate the process.
If $$E^o$$ is most positive for a metal than it will have least tendency to reduce and we will use roasting method to extract metal from its ore.

What is the formula of calamine?

Calamine is an ore of zinc. It is zinc carbonate with the formula, $$ZnCO_3$$.

Which one is the following ores is best concentrated by froth floatation method?
1.Galina
2.Malachite

$$1.Galina$$

Froth flotation method is used for the concentration of sulphide ores. The method is based on the preferential wetting properties with the frothing agent and water. In the given options, Galena (PbS) being a sulphide ore is concentrated by froth floatation process.

Early transition metals occur in nature as oxides but the late transition metals occur as sulphides.
If it is true enter 1, else enter 0.

The group 3 to 5 metals are often referred to as early transition metals and they are generally oxophilic and halophilic i.e the oxygen and halogens lovers. The later transition metals are placed in the right side of the periodic table and they mainly occur as sulphides.

ZnS is always contaminated with PbS. We add $$NaCN + ZnS$$ to enrich PbS by froth flotation process. If true enter 1 else 0.

$$\underset {(Zinc Blende)}{ZnS}$$ is always contaminated with $$\underset {(Galena)}{PbS}$$

Galena is concentrated by using a collector, potassium ethyl xanthate and sodium cyanamide and alkali as depressant. This is froth flotation process. Hence its True, 1.

Although iron is only about two-third as abundant as aluminium in Earth's crust but it costs only about one-quarter as much as required to produce aluminium.
If true enter 1, else 0.

Prduction of Iron doesnot require electrolysis.

The reduction process of alumina is done by electrolytic reduction in special reduction cell. This requires a huge amount of money. Hence, the cost of extraction of aluminium is more than that of iron though it is more abundant then iron.

When an inert atmosphere is needed for a metallurgical process, nitrogen is frequently used. However, in the reduction of $$TiCl_4$$ by magnesium, helium is used. This is because $$N_2$$ can combine with _____.

Nitrogen combines with magnesium upon heating to form magnesium nitride. It cannot be used to provide an inert atmosphere in this case. Therefore, helium [He] a noble gas is used to provide the inert atmosphere

$$2Mg+N_2\overset{\Delta}{\rightarrow}Mg_3N_2$$

Metals of high purity (to be used in semiconductors) are obtained by zone-refining.
If true enter 1, else enter 0.

Zone Refining (Fractional Crystallisation):
This method is employed to get metal of very high purity i,e. ultra pure samples of Ge Si, B,Ga,In. This method is based on the fact that impurities are more soluble than the pure metal in the melt .

______ is the most abundant element in the earth's crust.

Oxygen is the most abundant element in the Earth's crust. Oxygen makes up 467,100 ppm (parts per million) of the Earth's crust, or 46.6%.

Sulphur is extracted by Frasch process. If true enter 1 else 0.

Frasch method is a method to extract sulphur from the underground deposits. By this process the $$S$$ obtained is very pure.

Hence True, 1.

Most abundant metal in the earth's crust is _________.

Aluminium is the most abundant metal in the earth's crust, it is never found free in nature. All of the earth's aluminium has combined with other elements to form compounds.

The reducing agent used in thermite process is ___________.
Carbon
Aluminium
Iron
Sodium

Thermite process is very useful for the welding of broken metal parts. When Aluminum powder reacts with iron oxide or chromium oxide, a large amount of heat is released and about a temperature of $$3500^0C$$ is attained which is enough to weld broken metallic parts.

$$Mg$$ can be used to reduce $$TiCl_4$$ into $$Ti$$ in __________.
Monds
van Arkel
Hall
Kroll

Kroll collen process
$$TiCl_4 + 2Mg \rightarrow 2MgCl_2 +Ti$$

Differentiate between roasting and calcination.

In calcination the ore is heated in the absence of air where asIn roasting ore is heated in the presence of air.
calcination is done for carbonate ores where as Roasting is done for sulphide ores

Find the number of metals from the given metals which can be commercially purified by zone refining methods:
( Si, Ge, Ga, AI, Ti, Zr )

Three metals (Si, Ge and Ga) can be commercially purified by zone refining methods. These metals are used as semiconductors.

In froth floatation process in the concentration of sulphide ore froth adsorbs ore particles.
If true enter 1 else enter 0

Froth flotation is the process of selectively separating hydrophobic materials from hydrophillic.

In case of sulphide ores, the ore particles are adsorbed on froth that floats and the gangue particles settle down in tank. Hence true,1.

Among the following processes, how many are employed for the extraction of lead from ore galena?

(i) Self reduction , (ii) Carbon reduction , (iii) Metal displacement method , (iv) electrolytic reduction ,(v) Carbon monoxide reduction, (vi) Hydrogen reduction

Following three processes are employed for the extraction of lead from ore galena.
(i) Self reduction , (ii) Carbon reduction , (iii)Carbon monoxide reduction.
(i) Self reduction
$$PbS + 1/2O_2\longrightarrow PbO + SO_2\uparrow$$
$$PbS + 2PbO \longrightarrow 3Pb(l) + SO_2\uparrow$$
(ii) Carbon reduction
$$PbO + C \longrightarrow Pb(l) + CO_2 \uparrow$$
(iii)Carbon monoxide reduction.
$$PbO + CO \longrightarrow Pb(l) + CO_2\uparrow$$

Gallium arsenide is purified by __________ .
Froth floating process.
Zone-refining method.

Option 2.

This method is generally used to refine metalloids and ultra-pure metal is obtained.

hence gallium is a metalloid so gallium arsenide is purified by zone-refining.

MATCH THE COLUMN

Iron is obtained by carbon reduction method.
Lead is obtained by either carbon reduction method or self reduction.
Copper is obtained by either self reduction or by hydrometallurgical process.
Chromium is obtained by Thermite process.

Predict whether the following statement is true or false.
The most abundant metal in the earth's crust is Al.
If true enter 1,else enter 0.

True,

Element percent parts per million by weight

by weight

Oxygen 46.1% 461,000

Silicon 28.2% 282,000

Aluminum 8.23% 82,300

Iron 5.63% 56,300

Calcium 4.15% 41,500

Sodium 2.36% 23,600

Magnesium 2.33% 23,300

Potassium 2.09% 20,900

Titanium 0.565% 5,650

Hydrogen 0.14% 1,400

Match the following and select the correct answer from codes given below

Addition reaction:
$$\displaystyle R_{2}C=CR_{2}\rightarrow R_{2}CHCHR_{2}$$
Calcination
$$\displaystyle ZnCO_{3}\overset{\Delta }{\rightarrow}ZnO+CO_{2}$$
Roasting
$$\displaystyle 2ZnS+3O_{2}\overset{\Delta }{\rightarrow}2ZnO+2SO_{2}$$
Thermite Process
$$\displaystyle Fe_{2}O_{3}+2Al \rightarrow 2Fe+Al_{2}O_{3}$$

In the electrolytic refining of a metal $$M$$, what would you take as the anode, the cathode, and the electrolyte?

What is the role of depressant in froth floatation process?

Depressants prevent certain types of particles from forming froth with bubbles. Due to this, we can separate two sulphide ores.

For example, sodium cyanide is a depressant used for an ore containing $$ZnS$$ and $$PbS$$. $$NaCN$$ forms a layer of the complex $$\displaystyle Na_2[Zn(CN)_4] $$ on the surface of $$ZnS$$ and prevents it from forming a froth. Thus, it acts as a depressant. However, $$NaCN$$ does not prevent $$PbS$$ from forming froth and allows it to come with froth.

The choice of a reducing agent in a particular case depends on thermodynamic factor. How far do you agree with this statement? Support your opinion with two examples.

For the reduction of given metal oxide to metal, consideration of thermodynamic factors helps in selecting a suitable reducing agent. Ellingham diagrams (plots of $$\displaystyle \Delta _f G ^o$$ vs $$T$$) can predict the feasibility of thermal reduction. Metals with a more negative standard free energy of formation of oxides can reduce the metal oxides with a less negative standard free energy of formation of respective oxides. Metal will reduce the oxides of other metals which lie above it in Ellingham diagram as the standard free energy change for combined redox reaction will be negative by an amount equal to the difference in $$\displaystyle \Delta _f G^o$$ of two metal oxides. Thus, both $$Al$$ and $$Zn$$ can reduce $$FeO$$ to $$Fe$$ but $$Fe$$ cannot reduce $$\displaystyle Al_2O_3$$ to $$Al$$ or $$ZnO$$ to $$Zn$$. Also, $$C$$ can reduce $$ZnO$$ to $$Zn$$ but not $$CO$$.

State the role of silica in the metallurgy of copper.

During roasting, copper pyrites give $$FeO$$ and $$\displaystyle Cu_2O$$.
$$\displaystyle 2CuFeS_2 + O_2 \xrightarrow {\Delta} Cu_2S + 2FeS + SO_2$$

$$\displaystyle 2Cu_2S + 3O_2 \xrightarrow {\Delta } 2Cu_2O + 2SO_2$$

$$\displaystyle 2FeS + 3O_2 \rightarrow 2FeO + 2SO_2$$

Roasted ore is then mixed with silica (acidic flux) and heated to remove

$$FeO$$ (basic) as a slag of iron silicate.

$$\displaystyle FeO + SiO_2 \rightarrow FeSiO_3$$
Lighter slag forms upper layer and is removed through slag hole.

Write down the reactions taking place in different zones in the blast furnace during the extraction of iron.

In blast furnace, iron oxides are reduced at different temperature ranges. In the lower part of the blast furnace, the temperature is as high as $$2200\ K$$. It is called combustion zone. At the top, the temperature is as low as $$500 - 800\ K$$. It is called reduction zone. In the lower temperature range, carbon is the reducing agent and in the higher temperature range, $$CO$$ is the reducing agent. In the reduction zone ($$500-800\ K$$), following reactions occur.
$$\displaystyle 3Fe_2O_3 + CO \rightarrow 2Fe_3O_4 + CO_2$$
$$\displaystyle Fe_3O_4 + 4 CO \rightarrow 3Fe + 4CO_2$$
$$\displaystyle Fe_2O_3 + CO \rightarrow 2FeO + CO_2$$
In the temperature range 900-1500 K, following reactions occur.
$$\displaystyle C + CO_2 \rightarrow 2CO$$
$$\displaystyle FeO + CO \rightarrow Fe + CO_2$$
Around 1270 K (middle portion), decomposition of limestone gives lime ($$CaO$$) and $$\displaystyle CO_2$$. Lime is a flux and combines with silicate impurity to form slag of calcium silicate.
$$\displaystyle CaCO_3 \rightarrow CaO + CO_2$$
$$\displaystyle CaO + SiO_2 \rightarrow CaSIO_3$$

Out of $$C$$ and $$CO$$, which is a better reducing agent for $$ZnO$$?

Out of $$C$$ and $$CO$$, the better reducing agent for $$ZnO$$ is $$C$$.
$$\displaystyle ZnO + C \xrightarrow {1673 \: K} Zn + CO$$

Why copper matte is put in silica lined converter?

Copper matte contains $$\displaystyle Cu_2S$$ and $$FeS$$. Hot air blast converts $$FeS$$ to $$FeO$$. $$FeO$$ is removed as slag when it reacts with silica. Hence, copper matte is placed in silica lined converter.

$$\displaystyle 2FeS + O_2 \rightarrow 2FeO + 2SO_2$$

$$\displaystyle FeO + SiO_2 \rightarrow FeSiO_3$$

$$\displaystyle Cu_2S$$ or $$CuO$$ is converted to copper.

$$\displaystyle 2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2$$

$$\displaystyle 2Cu_2O + Cu_2S \rightarrow 6 Cu + SO_2$$

The value of $$\Delta_{f} G^{0}$$ for formation of $$Cr_{2} O_{3}$$ is $$-540\ kJmol^{-1}$$ and that of $$Al_{2} O_{3}$$ is $$-827 kJmol^{-1}$$. Is the reduction of $$Cr_{2} O_{3}$$ possible with $$Al$$?

$$\displaystyle \dfrac {4}{2}Al + O_2 \rightarrow \dfrac {2}{3} Al_2O_3 \: \Delta _f G^o (Al, Al_2O_3 = - 827 \: kJ/mol) $$......(i)

$$\displaystyle \dfrac {4}{3} Cr +O_2 \rightarrow \dfrac {2}{3} Cr_2O_3 \: \Delta _f G^o (Cr, Cr_2O_3) = - 540 \: kJ/mol$$ ......(ii)

Subtract equation (ii) from equation (i), we get

$$\displaystyle \dfrac {4}{3}Al + \dfrac {2}{3} Cr_2O_3 \rightarrow \dfrac {2}{3} Al_2O_3 + \dfrac {4}{3} Cr \: \Delta _r G^o = - 287 \: kJ/mol$$

Because, for the combined reaction, $$\displaystyle \Delta _r G^o < 0$$ (negative), the reaction is spontaneous and the reduction of $$\displaystyle Cr_2O_3$$ by $$Al$$ is possible.

How can you separate alumina from silica in a bauxite ore associated with silica? Give equations, if any.

Bauxite ore containing silica is heated with conc. $$NaOH$$ solution at $$473-523$$ K and $$35-36$$ bar pressure. Alumina forms sodium aluminate and silica forms sodium silicate. Impurities are left behind.
$$\displaystyle Al_2O_3 + 2NaOH +3H_2O \rightarrow 2Na[Al(OH)_4]$$
Carbon dioxide neutralizes the aluminate to precipitate hydrated alumina.
$$\displaystyle 2Na[Al(OH)_4] +2CO_2 \rightarrow Al_2O_3.xH_2O + 2NaHCO_3$$
Sodium silicate remains in the solution and hydrated alumina is filtered and dried. On heating, hydrated alumina gives pure alumina.
$$\displaystyle Al_2O_3.xH_2O \xrightarrow {1473\ K} Al_2O_3(s) + xH_2O$$

How is leaching carried out in case of low grade copper ores?

Acid in presence of air is used to leach out copper from low grade copper.
$$\displaystyle Cu + 2H^+ + 0.5 O_2 \rightarrow Cu^{2+} + 2H_2O$$

Solution is then treated with scrap iron or hydrogen.
$$\displaystyle Cu^{2+} + H_2 \rightarrow Cu + 2H^+$$

Write the principle behind the froth floatation process. What is the role of collectors in this process?

Froth floatation process is based on the principle that the metallic sulphide particles of ore are preferentially wetted by oil and the gangue particles by water.
Collectors attach themselves by polar groups to grains of minerals which then become water repellent and thus, pass on into the froth. Examples are ethyl xanthate and potassium ethyl xanthate.

What chemical process is used for obtaining a metal from its oxide?

The chemical process which is used for obtaining a metal from its oxide is known as reduction. In this process, metal oxides are reduced to their respective metals by using suitable reducing agents such as carbon or by using some highly reactive metals to displace the metals from their oxides.

For example, zinc oxide is reduced to metallic zinc by heating with carbon.

Write the principles of the following methods.
(i) Froth floatation method
(ii) Electrolytic refining

(i) It is based on the difference in wetting qualities of gangue and the sulphide are particles with water and oil. Whereas the ore particles are wetted by oil, the gangue or the earthy particles are wetted by water.

(ii) In electrolytic refining process a slab of impure copper is used as anode and a thin sheet of pure copper as cathode. The copper sulphateis used as electrolytic solution. By passing electricity through the cell copper is dissolved from the anode and deposited on cathode. The impurities either remain in solution or collect as an insoluble gangue.

(i) Name the method of refining to obtain silicon of high purity.
(ii) What is the role of $$SiO_{2}$$ in the extraction of copper?
(iii) What is the role of depressants in froth floatation process?

(i) Zone Refining is the method of refining to obtain silicon of high purity.

(ii) $$SiO_2$$ combined with the iron in the copper ore to from iron (II) silicate slag which is easily removed.

$$FeO+SiO_2\longrightarrow FeSiO_3$$

(iii) In froth flotation process, depressant prevents the formation of froth. It is used to separate two sulphide ore and allowing the other to form the froth, e.g., $$NaCN$$ a depressant selectively $$ZnS$$ from coming in froth but allows $$PbS$$ to come with the froth.

What is the role of collectors in froth flotation process?

Collectors are reagents that are used to selectively adsorb onto the surfaces of particles. A monolayer is formed by the collectors on the particle surface that essentially makes a thin film of non-polar hydrophobic hydrocarbons. The collectors greatly increase the contact angle so that bubbles will adhere to the surface.

Give an example of zone refining of metals.

It is based on the principle that when an impure metal in a molten state is allowed to cool, only the metal crystallizes while the impurities remain present in the molten state (mass) or melt. The impure metal converted into a rod which is heated at one end with a circular heater. This method is used for refining metals having a low melting point. e.g., tin, lead, bismuth.

Outline the principles of refining of metals by the following methods:
(i) Zone refining (ii) Vapour phase refining

(i) Zone refining: This method is based on the principle that impurities are more soluble in the molten state of metal (the melt) than in the solid state. In the process of zone refining, a circular mobile heater is fixed at one end of a rod of impure metal. As the heater moves, the molten zone of the rod also moves along with it. As a result, pure metal crystallizes out of the melt and the impurities pass to the adjacent molten zone. This process is repeated several times, which leads to the segregation of impurities at one end of the rod. Then, the end with the impurities is cut off. Silicon, boron, gallium, indium etc. can be purified by this process.

ii) Vapour phase refining: It is the process of refining metal by converting it into its volatile compound and then, decomposing it to obtain a pure metal. To carry out this process-
a. The metal should form a volatile compound with an available reagent, and
b. The volatile compound should be easily decompose so that the metal can be easily recovered. Nickel, zirconium, and titanium are refined using this method.

Iron is not found naturally in the form of the free metal. Gold can be found naturally as the free metal. Explain.

Gold is a noble metal and it does not react with any other element easily to make a compound. Hence, Gold can be found naturally as the free metal. On the other hand, iron is stable after formation of oxides hence, Iron is not found naturally in the form of the free metal.

The principle of difference in boiling points of liquid is used in the _______.

Principle of difference in boiling points of liquid is used in the process of Distillation. Distillation is a traditional technique used to separate and purify liquids in the industry.

Why gangue is removed from an ore?

In mining, gangue is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. Gangue is an impurity. Hence, to obtain pure metal gangue is removed from the ore.

Which of the following ores can be concentrated by froth floatation method and why?
$$Fe_{2}O_{3}, ZnS, AI_{2}O_{3}$$

Froth floatation is the process employed for the extraction of metals from their sulphide ores like $$ZnS$$.

A mixture of barium sulphate and H$$_2$$O can be separated by the method of ...................

Barium sulphate is insoluble in water so they're easily separated by simple filtration.

Prepare by adding together and let precipitate get coarse by boiling and cooling down

$$Ba(OH)_2 + H_2SO_4 \rightarrow BaSO_4 + H_2O$$

Later on filtrate off the water.

What are ellingham diagrams ? Write any two features of it.

Ellingham diagram : The graph plotted $$\Delta G$$ against $$TK$$ for the formation of oxide is called as Ellingham diagram.

(a) The graph for the formation of metal oxide is a straight line with an upward slope.
(b) There is sudden change in the slope of some metal oxides such as $$MgO$$, $$ZnO$$ and $$HgO$$.
(c) For a few metal oxides of mercury and silver the graph is at the upper part in the Ellingham diagram ($$AgO$$ and $$HgO$$).

Write short notes on froth floatation process?

Froth flotation is a method which employs a mixture of water and pine oil which is made to forth in a tank to separate sulphide ores. The differences in the wetting properties of the ore and gangue particles separate them.

The ___________ minerals are the compounds of metal with sulphur.

Minerals of metals with sulphur are called $$sulphide$$ minerals. Some of the sulphide minerals are shown below.

Argentite $$(Ag_2S)$$
Galena $$(PbS)$$
Chalcocite $$(Cu_2S)$$
Copper pyrite (chalcopyrite) $$(CuFeS_2)$$

∴ Sulfide containing ores are Ag, Cu, Pb.

Explain why: In the electrolysis of alumina using Hall Heroult's Process the electrolyte is covered with powdered coke.

The layer of powder coke prevents the burning of carbon electrodes in air at the point where they emerge from the bath. It also reduces the heat loss.

Identify the term/substance in each of the following :
(i) The tendency of an atom to attract electrons to itself when combined in a compound.
(ii) The method used to separate ore from gangue by preferential wetting.
(iii) The catalyst used in the conversion of ethyne to ethane.
(iv) The type of reactions alkenes undergo.
(v) The electrons present in the outermost shell of an atom.

(i) The tendency of attracting electrons towards itself is known as electron affinity.

(ii) Froth floatation method is used for separation of ore from gangue by preferential wetting.Ore is wetted by the oil hence floats on top as a foam and gangue is wetted by the water and settles down.

(iii) Nickel is used as a catalyst for the conversion of ethyne to ethane.It is an addition reaction.

(iv) Alkenes undergo addition reactions.

(v) The outermost shell electrons that take part in chemical reaction are known as Valence Electrons.

Write a short note on gangue and anode mud.

Gangue are the earthly impurities that are accompanied with the minerals during their extraction.

A deposit of insoluble residue or mixture that collects at the anode in an electrolytic refining and formed from the dissolution of the anode in commercial electrolysis or plating process. The soluble impurities go into the solution. Also, it is sometimes called anode slime.

Which method do you suggest for extraction of high reactivity metals? Why?

High reactive metals such as aluminium, calcium and sodium are extracted from their ores by the electrolytic reduction. These highly reactive metals cannot be reduced by using carbon as it is less reactive. In this method the electric current is passed through the ores to get the pure metals.

Explain the purification of sulphide ores by froth floatation method?

The purification of Sulphide ores by froth floatation method:
This method is used for the concentration of sulphide ore such as galena $$(PbS)$$, zinc blende $$(ZnS)$$ and copper pyrites $$(CuFeS_2)$$
To water tank, finely divide ore is added. Pine oil, eucalyptus oil, xanthates or fatty acids etc are added. Compressed air is passed through water tank.
Metallic sulphide particles of ore are preferentially wetted by oil. They rise to the surface along-with froth.
The gangue particles are wetted by water. They settle at bottom.

Name the refining method used to produce semiconductors.

Zone refining is used to produce semiconductors.A circular heater is fitted around a rod of impure metal and is slowly moved down the rod. At the heated zone, the rod metls and as the heater passes on, pure metal crystallizes while impurities pass into the adjacent molten part. In this way, the impurities are swept over one end of the rod, which is finally discarded. The heater may have to be moved from one end to the other more than once. Ge, Si and ga used as semiconductors are refined in this manner; gallium-arsenide and indium-antimonide are also zone refined.

Explain calcination and roasting with example.

Calcination : Ore is heated to a high temperature below its melting point in the absence of dry air or in a limited supply of air. Organic matter, moisture, volatile impurities like carbon dioxide and sulphur dioxide are expelled from the ore. It makes ore porous. Decomposition of carbonate ores gives metal oxides and carbon dioxide.
$$\displaystyle ZnCO_3 \xrightarrow {\Delta} ZnO(s) +CO_2(g)$$

Roasting:
Ore is heated to high temperature below melting point in presence of excess air. Moisture escapes and impurities of sulphur, arsenic, phosphorous etc are oxidized to volatile oxides. It makes mass porous. During extraction of magnesium, roasting is used for magnesite.
$$\displaystyle S+O_2 \rightarrow SO_2 \uparrow $$
$$ \displaystyle 2ZnS +3O_2 \rightarrow 2ZnO +2SO_2 \uparrow$$

Draw the diagram showing froth floatation method and label its parts.

REF.Image.

Froth floatation process for the

concentration of sulphide ores.

(a) Explain the following.
(i) Roasting
(ii) Calcination.

(b) What are amphoteric oxides? Write the name of such one oxide.

(c) By which two metals is brass alloy formed?

(a)

(i) Roasting is the process in which the ore is heated below its melting point in presence of air to oxidise the impurities. eg: carbon, sulphur, etc removed as their gaseous oxides.

(ii) Calcination is the process of heating the ore below its melting point absence of air to remove volatile impurities like arsenic etc.

(b) In chemistry, an amphoteric compound is a molecule or ion that can react both as an acid as well as a base. Many metals (such as copper, zinc, tin, lead, aluminum, and beryllium) form amphoteric oxides or hydroxides. Amphoterism depends on the oxidation states of the oxide.

(c) Brass is a metal alloy made of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.

What is a concentration of ores? Explain the process with diagram by which metallic ore with sulphide as an impurity is purified.

1. The ores are concentrated on the basis of the type of impurities and their percentage proportions. As a result, most of the impurities are removed and the proportion of the ore is increased. This process is called concentration of the ore. For this, (i) concentration or centrifugation on the basis of difference in densities (ii) froth floatation and (ii) magnetic separation methods are used.

2. Froth floatation method is used for concentration of the ores of the metals whose ores are in sulphide form. The concentration of sulphide ores of copper, lead and zinc metal are carried out by this method. In this method, the fine powder of the ore, and water are filled in a big vessel. Substances like pine or turpentine oil are added to it.

3. The sulphide particles of the metals get wet and stick to it, while clay, particles of sand, do not get wet. In this liquid mixture, air is passed with pressure through a tube. Hence, the froth is produced around the light particles of the liquid mixture. Heavy particles like clay, sand etc. become wet by water and settle down at the bottom

4. The sulphide ore of metal is removed with sieves in a second vessel and washed with water. By this method, ores like copper pyrites are concentrated and clay, sand etc. are removed.

What is the role of depressants in the forth floatation process?

In the froth floatation process, the role of the depressants is to separate two sulphide ores by selectively preventing one ore from forming froth.

The impurities which are not removed during ore concentration are called .........
(Gangue, flux, slag)

The impurities which are not removed during ore concentration are called gangue. Flux is the substance added to molten metals to bond with impurities that can be removed later. Slag is the waste material which is removed during smelting or refining of ore.

Write the name of the metal whose ore is siderite.

Siderite is a mineral composed of iron (II) carbonate (FeCO3).

Draw labelled diagram of Hall-Heroult Electrolytic cell for the extraction of aluminium. Write anode and cathode reactions.

Elemental aluminium can't be prepared by the electrolysis of an aqueous aluminium salt because hydronium ions easily oxidize elemental aluminium. Although a molten aluminium salt could be used instead of it, aluminium oxide has a melting point of $$2072^0C$$ so electrolysing it is impractical. In the Hall–Héroult process, alumina, $$Al_2O_3$$, is dissolved in molten synthetic cryolite, $$Na_3AlF_6$$, to lower its melting point for easier electrolysis.

What is refining of metals? Explain with diagram the method of electrolysis by which copper is purified.

The metal obtained by reduction method is not very pure. The method to obtain about hundred percent pure metal by removing impurities present in very small amounts in the metal is called refining.
Refining of copper metal is carried out by the electrolysis method: The rod of impure copper is arranged as the anode and the rod of pure copper is arranged as a cathode. The aqueous solution of copper sulphate is taken as the electrolyte. A little dilute sulphuric acid is added to it. When an electric current is passed through the electrolyte, the proportion in which copper from the anode is dissolved in aqueous solution of copper sulphate, copper in the same proportion from copper sulphate solution is deposited at the cathode. Thus, the copper deposited at the cathode in this way has almost 100% purity.
Anode (Positive pole): $$Cu(s)$$ (Impure) $$\rightarrow$$ $$Cu_2+(aq) + 2e^-$$ (oxidation)
Cathode (Negative pole): $$Cu^{2+}$$ (aq) + 2e- $$\rightarrow$$ $$Cu(s)$$ (reduction)
Net reaction: $$Cu(s)$$ (Impure) $$\rightarrow$$ $$Cu(s)$$ (Pure)

Explain magnetic separation process of ores with the help of a neat, labelled diagram.

Magnetic separation process of ores:
An electromagnetic separator is required. A leather or brass belt moves over two rollers, one of which encloses magnets in it. The powdered ore is dropped over this moving belt at one end. The non magnetic part of the ore is not attracted by the magnet and falls to form a separate heap at a distance. The magnetic part of the ore clings to the belt for a longer distance and forms another heap near the magnet.

For example, nonmagnetic $$\displaystyle SnO$$ is separated from magnetic $$\displaystyle FeWO_4$$ present in the ore $$\displaystyle Cassiterite$$ by magnetic separation process.

The metal whose oxide, which is amphoteric, is reduced to metal by carbon reduction ___________. $$(Fe/ Mg/ Pb/ Al)$$.

The metal whose oxide, which is amphoteric, is reduced to metal by carbon reduction

PbPb.
Amphoteric substances reacts with acids as well as bases.
$$ \displaystyle PbO+2HNO_3 \rightarrow Pb(NO_3)_2+H_2O$$
$$ \displaystyle PbO+2NaOH \rightarrow Na_2PbO_2+H_2O$$

On heating with carbon, $$ \displaystyle PbO$$ is reduced to Pb.
$$ \displaystyle PbO+C \rightarrow Pb+CO$$
$$ \displaystyle PbO+CO \rightarrow Pb+CO_2$$

Explain zone refining.

Zone Refining is the most important of the zone-melting techniques. In zone refining by passing a number of molten zones through it in one direction. Each zone carries a fraction of the impurities to the end of the solid charge thereby purifying the remainder.

Principle of Zone Refining are quite general and so the method has been applied to many substances. More than $$1/3^{rd}$$ of the elements and hundreds of inorganic & organic compounds have been raised to their highest purity by zone refining. Many of these were, for the first time made pure enough for their intrinsic properties to be determined.

Explain zone - refining (figure not necessary).

The process of zone refining follows the principle that impurities in a metal are more soluble when the metal is in the molten state than when it is in the solid state. Therefore, in the zone refining method, a circular mobile heater is attached to a metal rod (made of impure metal) at one end. The heater is moved and so does the molten zone of the rod. The pure metal gets removed from the melt through crystallization while the impurities pass on into the adjacent zone of molten metal. If this process is repeated, the impurities are gradually removed from the metal. The impurities finally accumulate at one end and this end can be cut off.

Write reactions involved in extraction of silver from it's ore by leaching process. O-nitrophenol is more acidic than O-cresol; Explain.

leaching process for silver.

$$Reaction :- Ag_2S+4Na CN \rightarrow 2Na [Ag (CN)_2]+Na_2S $$

Ortho nitrophinol is morl acidic then cresol bcoz

the nitro groups is an electron -withdrawing graph the presence of this group in the ortho posn in $$O-$$nithophenol decreases the election in the $$O-H$$ bond. as a result, it is easier to loss a proton.

In case of $$O-$$cresol, methony groups is an edg yhus it increases the $$e^-$$ density in the $$O-H$$ bond and hence, the proton cannot be given out easily.

A trivalent Metal "M" occurs in nature in the form of its oxide $$M_{2}0_{3}$$. The metals is widely used in making household utensils and bodies of aircraft.
(i) Identify the metal
(ii) Name the chief ore of metal
(iii) Write down the reaction involved during the extraction of metal with figure.

$$Al_2O_3 + 2NaOH \rightarrow 2NaAlO_2 + H_2O $$

$$NaAlO_2 + 2H_2O \rightarrow NaOH + Al(OH)_2$$

the bauxite is purified to yield a white powder , aluminum oxide , from which aluminum can be extracted . the extraction is done by electrolysis. But first the aluminum oxide must be made molten. So that electricity can pass through it.

During the extraction of aluminium by Hall-He'roult process,
i) Write a neat labeled diagram of the electrolytic cell.
ii) Write over all cell reaction.
iii) At which electrode oxygen gas is liberated?

During the extraction of aluminium by Hall-He'roult process,
i) Neat labelled diagram of electrolytic cell is as shown.
ii) Over all cell reaction is $$2Al_2O_3+3C\rightarrow 4\ddot{Al}+3CO_2$$.

iii) At anode oxygen gas is liberated.

$$ \displaystyle C+O^{2-} \rightarrow CO+2e^-$$
$$ \displaystyle C+2O^{2-} \rightarrow CO_2+4e^-$$
At cathode, Al is obtained.
$$ \displaystyle Al^{3+}+3e^- \rightarrow Al$$

How many of the given metals can be obtained by carbon reduction in their extractive metallurgy.
Cu, Zn, Pb, Na, Sn, Ag, Au, Mg, Al, Fe

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Lemon or tamarind is used for cleaning copper vessel turned greenish.
Comment on the above statement.

1) Copper reacts with carbon dioxide in the air to form copper carbonate.

2) As a result, copper loses its shiny brown surface forming a green layer of copper carbonate.

3) The citric acid present in the lemon or tamarind neutralizes the basis copper carbonate and dissolves the layer.

4) Therefore, tarnished copper vessels are cleaned with lemon or tamarind juice to give luster to the surface of the copper vessel.

ZnS and PbS are separated by using?

$$ZnS$$ and $$Pbs$$ are separated by froth flotation process, depressant helps to separate two sulphuric ores by selective preventative of froth formination by one come into forth, in order to separate two sulphur ores[Zns and Pbs].

$$NaCN$$ is used as depressant.

Which of the metal ores can be obtained in hydrometallurgical reduction?

Hydrometallurgy is a process in which development of ions exchange, solvent extraction and other process has led to extraction of ore than 70 metallic elements. Gold and silver are produced using metallurgy recently copper and zinc are also produced.

Explain briefly the extraction of aluminium from bauxite.

The extraction of the metal from bauxite involves the three main steps.

Concentration of Bauxite $$\left( {Al}_{2}{O}_{3}.2 {H}_{2}O \right)$$

Concentration of ore is done by leaching which helps in removing impurities like $${Fe}_{2}{O}_{3}, Si{O}_{2}$$, etc. Bauxite is treated with $$NaOH$$ to form sodium aluminate which on further reaction with $$C{O}_{2}$$ gives pure Alumina.

$${Al}_{2}{O}_{3} + 2 NaOH + 3 {H}_{2}O \longrightarrow 2 Na \left[ Al {\left( OH \right)}_{4} \right] \xrightarrow[-2 NaHC{O}_{3}]{2 C{O}_{2}} {Al}_{2}{O}_{3}.x{H}_{2}O \xrightarrow[1470 \; K]{\Delta} \underset{\text{Pure alumina}}{{Al}_{2}{O}_{3}} + x {H}_{2}O$$

Electrolytic reduction of Alumina $$\left( {Al}_{2}{O}_{3} \right)$$

Electrolytic reduction of pure alumina takes place in iron box (cathode) with cryolite $$\left( {Na}_{3}Al{F}_{6} \right)$$ and fluorspar $$\left( Ca{F}_{2} \right)$$ which lowers the melting point and increases the conductivity of electrolyte. Graphide rods act as anode.

At cathode:-

$${Al}^{3+} + 3 {e}^{-} \longrightarrow Al$$

At anode:- The oxygen liberated at anode reacts with the carbon of anode to produce $$CO$$ and $$C{O}_{2}$$.

$$C + {O}^{2-} \longrightarrow CO + 2{e}^{-}$$

$$C + 2 {O}^{2-} \longrightarrow C{O}_{2} + 4 {e}^{-}$$

By this process $$98.8 \%$$ pure aluminium is obtained.

Which elements occurs in its native or elemental stage?

$$\bullet$$ Any of a number of chemical elements which occur uncombined with other elements are called native elements. OR

The elements which have low reactivity because of which they do not react with air, moisture, oxygen gas, etc. are occurred as in the native state.

For example Gold, silver, platinum, etc,

In Bayer's process leaching is carried out using:

The seperation of the alumina from the impurities in the baurite ore is usually accomplished by bayer process. The bauxite ore is leachedwith caustic soda (NaOH) to produce soluble sodium Aluminate $$(NaAlO_2)$$ leaving the impurities in the insoluble residue. The aluminate solution is then decomposed producing $$Al(OH)_3$$ which is calcined to produced $$Al_2O_3$$ so, leaching is carried ot by caustic soda

What is the function of collectors in the froth floatation process for the concentration of ores?

Collectors (e.g., pine oil, xanthates etc.) enhance non-wettability of the ore particles.

Why is it that only sulphide ores are concentrated by froth floatation process?

This is because the sulphide ore particles are preferentially wetted by oil and gangue particles are preferentially wetted by water.

What is metallurgy ?

Branch of science, which deals with the extraction of metals from their ores, is known as metallurgy.

Explain the purification of sulphide ore by Froth floatation method.

Purification of Sulphide ore by froth floatation method $$\rightarrow$$

This method employs a mixture of water and pine oil which is made to froth in a tank to separate sulphide ores. The differences in the wetting properties of the ore and gangue particles separate them.

A mixture of water, pine oil, detergent, and powdered ore is first taken in a tank. A blast of compressed air is blown through the pipe of a rotating agitator to produce froth. The sulphide ore particles are wetted and coated by pine oil and rise up along with the froth (froth being lighter). The gangue particles wetted by water sink to the bottom of the tank (water being heavier). Sulphide being more electronegative attracts the covalent oil molecules. The gangue being less electronegative is attracted by the water. The froth containing the sulphide ore is transferred to another container, washed, and dried.

1188605_1468893_ans_3dacbbe3ece94d0ca17ed9d852c6aea1.png

Although carbon and hydrogen better reducing agents but they are not used to reduced metallic oxides at high temperatures. Why?

It is because at high tempreature carbon and hydrogen react with metals to form carbides and hydrides respectively.

Name the anode and the cathode used in the electrolytic refining of impure copper metal.

Cathode	Pure Copper
Anode	Impure Copper
Electrolyte	Copper Solution

$$\textbf{Additional information}$$

The process of electrolysis is used to purify impure copper with the help of current.

$$\bullet$$Anode: The anode used for this process is made up impure.

$$\bullet$$Cathode: The cathode used for the electrolysis is pure copper sheets.

$$\bullet$$Electrolyte: Copper sulphate solution is used as an electrolyte in this process.

$$\bullet$$The impurities from the copper cathode start accumulating at the anode and at the bottom of the electrolytic cells once the current is passed through them; purifying the copper.

Write an example for a metal which can be refined by liquation?

Those metals which have low melting points can be refined by liquation.

E.g.- Tin can be refined by liquation.

Describe the extraction of two metals and two non-metals by electrolysis.

What happens when $$NaCN$$ is added in ore containing $$PbS$$ and $$ZnS$$ during concentration by froth floatation method?

$$NaCN$$ is used as a depressant which selectively allows $$PbS$$ to come with froth, but prevents $$ZnS$$ from coming to froth. This happens because $$NaCN$$ reacts with $$ZnS$$ to form $${Na}_{2} \left[ Zn{\left( CN \right)}_{4} \right]$$.

$$4 NaCN + ZnS \longrightarrow {Na}_{2} \left[ Zn {\left( CN \right)}_{4} \right] + {Na}_{2}S$$

How are metals used as semiconductors refined? What is the principle of the method used?

Metals of high grade like germanium, silicon etc., used as semiconductors are refined by zone refining method.

Principle:

This method is based upon the principle that impurities are more soluble in molten state of metal than in solid state.

How many ores are sulphide ores from the given ores?

Azurite, Chalcocite, Iron pyrites, Limonite

Azurite = $$2 CuCO_3.Cu(OH)_2$$

Chalcocite = $$Cu_2S$$

Iron pyrites = $$FeS_2$$

Limonite = $$Fe_2O_3.3H_2O$$

Wrought iron is the purest form of iron. Write a reaction used for the preparation of wrought iron from cast iron. How can the impurities of sulphur, silicon and phosphorus be removed from cast iron?

$$Fe_2O_3 + 3C \rightarrow 2Fe + 3CO$$

Limestone is added as flux and sulphur, silicon and phosphorus change to their oxides and pass into the slag.

What is the role of flux in metallurgical processes?

Flux is any substance introduced in the smelting of ores to promote fluidity and to remove impurities in the form of slag.

Role of flux in the metallurgical process:

(I) flux is used to remove the gangue by combining with it. Thus, slag formation takes place.

(ii) It makes the molten mass more conducting.

Why are sulphide ores converted to oxide before reduction?

Sulphide ores are converted to oxide before reduction because sulphide are not reduced easily while oxides can be reduced easily.

Therefore, sulphides are first oxidized and then subjected to reduction.

In the thermite process, __________ is used as a reducing agent.

In the thermite process, aluminium is used as a reducing agent.

A mixture of concentrated oxide ore and aluminium powder, commonly called as thermite, is taken in a steel crucible placed in a bed of sand.

$$Cr_2O_3 + 2Al \rightarrow 2Cr + Al_2O_3$$

$$3Mn_3O_4 + 8Al \rightarrow 9Mn + 4 Al_2O_3$$

A large amount of heat energy is released during reduction, which fuses both the alumina and the metal. Aluminium acts as a reducing agent and is itself oxidized.

Each of the following statements is true only under some specific conditions. Write the condition for each sub-question in not more than two sentences.
(i) Metals can be recovered from their ores by chemical methods.
(ii) High purity metals can be obtained by zone refining method.

(i) Many metals occur in nature as oxides, carbonates, sulphides which can be calcinied or roasted. Then, they can be further treated chemically to get the metal.

(ii) Elements such as Si, Ge, Ga etc., which are used as semiconductors, are refined by zone refining method. Highly pure metals are obtained. The method is based on the difference in solubility of impurities in the molten and solid-state of the metal.

A movable heater is fitted around a rod of the impure metal. The heater is slowly moved across the rod. The metal melts at the point of heating and as the heater moves on from one end of the rod to the other end, the pure metal crystallizes, while the impurities pass on to the adjacent molten zone.

Write down the reactions involved in the extraction of Pb. What is the oxidation number of lead in litharge?

Lead is mainly extractd from sulphide ore called galena. Roasting is done followed by reduction with carbon. Self-reduction finally takes place.

$$2PbS + 3O_2 \rightarrow 2PbO + SO_2$$
$$PbS + 2O_2 \rightarrow PbSO_4$$
$$PbSO_4 + PbO \rightarrow 2Pb + 2SO_2$$
$$PbS + 2PbO \rightarrow 3Pb + SO_2$$

Litharge is chemically $$PbO$$, and te oxidation state of lead is +2.

Explain the following:

Carbon and hydrogen are not used as reducing agents at high temperatures.

Carbon and hydrogen are not used as reducing agents for metals at high temperature because carbon and hydrogen react with metals to form carbides and hydrides, respectively, at high temperature.

Name the following:
Two metals which always occur both in native and in combined states.

The metal found in nature and which occurs both in the free and the combined state is generally known as the pure metals.

Example: Copper and Silver

Name the following:
Two metals which always occur naturally in an uncombined states.

$$Au, Pt$$ i.e.Gold and platinum occur in nature in an uncombined state.

Which one out the two many be found in native state?

Iron and silver

Silver is found in native state due to its less reactive nature.

Name the diagram which can be used to compare the reducing nature of the different elements.

An Ellingham diagram is a graph showing the temperature dependence of the stability of compounds. This analysis is usually used to evaluate the ease of reduction of metal oxides and sulfides.

Name the following:
Two metals which never occur in native state.

It is extremely difficult for the metal sodium and magnesium to exist in free state. In fact metals like sodium and potassium react vigorously with water even at low temperatures.

Write short note on:
Autoreduction

It is the process in which sulphide ores of less electropositive metals like $$Hg, Pb, Co$$ etc. are heated in air so that a part of the ore is converted into oxide ore which in turns react with remaining suplhide ore in absence of air to give the metal and sulphur dioxide.

Example: $$Cu_2S + O_2 \rightarrow CuO +SO_2$$

$$Cu_2S + CuO \rightarrow Cu + SO_2$$

Write short notes on:
Reverberatory

A reverberatory furnace is a metallurgical process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases.

A reverberatory furnace in copper, tin and nickel production, a furnace used for smelting and refining in which fuel is not in directly contact with ore but heats it by a flame blown over it from another chamber. In steel making this process called open-hearth process. In this process heat passes over hearth in which ore is placed and reverberates back.

Which ores generally concentrated by forth floatation process?

Sulphide ores are concentrated by the froth floatation process and it is based on the fact that gangue and ore particles have a different degrees of wetability with water and pine oil.

Answer the following
Name the metal which is commonly used as a reducing agent in metallurgical operations.

1687193_1727932_ans_4f564e51ad074e3886a749880981b6c4.jpg

Name two principal ores of each of the following metals:
Iron

Two principal ores of iron minerals are hematite and magnetite.

Answer the following:

Write the two important minerals of fluorine.

Fluorspar $$ ( CaF_2); Cryolite ( Na_3AlF_6 ) $$ these are two minerals of fluorine.

What happens when : manganese dioxide is heated with aluminium powder ?

When manganese dioxide $$ (MnO_2) $$ is heated with aluminium powder , displacement reaction takes place , and manganese is obtained as the product along with aluminium oxide. It is an exothermic reaction and hence Mn is obtained in molten form.

$$ 3 MnO_2 (s) + 4Al(s) \rightarrow 3Mn(l) + 2Al_2O_3(s) + $$ heat

What is liquation?

Liquation is a method of refining of metals and is used when the impurities are not miscible with the metal and the melting temperature of the metal is lower than that of the impurities.

Make a flowchart to explain the various steps involved in extraction of metals from ores .

Flowchart : Extraction of metals from ores
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What happens when iron(III) oxide is heated with aluminium powder ?

Iron (III) oxide is heated with aluminium powder to form iron and aluminium oxide. This is another example of a displacement reaction and is highly exothermic. This reaction is also known as thermit reaction .

$$ Fe_2O_3(s) + 2Al (s) \rightarrow 2Fe(l) + Al_2O_3(s) $$ + Heat

Define the term Mineral .

An element or compound which occurs naturally in the Earth's curst is called a mineral.

Define the term Ore .

Mineral which contains a very high percentage of a metal and from which the metal can be economically extracted is called an ore.

An ore sample of galena $$(PbS)$$ is contaminated with zinc blende $$(ZnS)$$. Name one chemical which can be used to concentrate galena selectively by froth floatation method.

$$NaCN$$ (sodium cyanide) is used as a depressant to concentrate galena selectively by froth floatation method.

What name is given to carbon reduction process for extracting the metal?

Smelting is used as a carbon reduction process to extract the metal .

What is gangue?

The earthy and silicious impurities associated with the ores are called gangue.

Why is it advantageous to roast a sulphide ore to the oxide before reduction?

The standard free energies $$(\triangle_{f}G^{\circ})$$ of formation of most of the sulphides are greater those of $$CS_{2}$$ and $$H_{2}S \ (CS_{2}$$ is in fact, an endothermic compound).

Therefore, neither carbon nor hydrogen can reduce metal sulphides to metal. In contrast, the standard free energies of formation of oxides are much lower than that of $$CO_{2}$$ and hence oxidation of metal sulphides to metal oxides is thermodynamically favourable.

Therefore, it is the common practice to roast sulphide ore to the oxide before reduction.

State briefly the principles involved in the following operations in metallurgy. Give an example.
Zone refining.

This method of refining of metals is based on the principle that the impurities are more soluble in molten state than in the solid state of the metal. Germanium, silicon, boron, gallium and indium are refined by this method.

Two ores A and B were taken. On heating ore A gives $$CO_2$$ whereas, ore B gives $$SO_2$$.
What steps will you take to convert them into metals?

When a carbonate ore is heated, we get carbon dioxide. A carbonate ore is calcinated to obtain oxide of the metal. Following equation shows calclnations of zinc carbonate.
$$ZnCO_3 \rightarrow ZnO + CO_2$$
When a sulphide ore is roasted, we get Sulphur dioxide. Zinc sulphide is roasted to obtain zinc oxide.
$$2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2$$
After any of the above steps; zinc oxide is reduced to obtain pure zinc.
$$ZnO + C \rightarrow Zn + CO$$

Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?

It is easier to obtain a metal from its oxide than from its sulphides or carbonates. Hence, in the process of extraction of metal from metal sulphides and carbonates, they are first converted to metal oxides.

What is the principle of the method used for refining metals used as semiconductors?

The method used for refining of semiconducting metal is based on the principle that the impurities are more soluble in melt than in the solid state of metals.

Answer the following questions:
What is the role of collectors in the froth floatation process? Give an example of a collector.

Collectors enhance non-wettability of the ore particles in the froth floatation process, e.g., pine oils, fatty acids, xanthates, etc.

Mention two uses of the following metals and non-metals:
Aluminium

1. It is used to make electric wires.

2. It is used to make utensils, cans, window frames, etc.

Give an example of a sulphide ore which reduced to metal by heating alone, i.e., by roasting.

Cinnabar (HgS) on roasting is first changed to mercuric oxide which on further
$$2HgS(s) + 30_{2}(g) \overset{Heat}{\rightarrow} 2HgO(s) + 2SO_{2}(g)$$

$$2HgO(s) \overset{Heat}{\rightarrow} 2Hg(l) + O_{2}(g)$$

Account for the following facts:
Pine oil is used in the froth floatation process used to concentrate sulphide.

Pine oil (collector) enhances the non-wettability of the ore particles, which becomes lighter and hence rise to the surface along with the froth.

Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores.

During extraction of metals of low and medium reactivity, a respective sulphide ore is first heated in air. This helps in obtaining oxide of metal. It is easier to extract a metal from its oxide rather than from its sulphide. Hence, this step is used. Mercury is a metal of low reactivity.
Mercury sulphide (cinnabar) is heated in air. Mercury sulphide gets oxidized to produce mercury oxide.
$$2HgS + 3O_2 \rightarrow 2HgO + 2SO_2$$
After that, mercury oxide is reduced to obtain mercury.
$$2HgO \rightarrow 2Hg + O_2$$
Zinc is a metal of medium reactivity. It is found as zinc blende (ZnS).
Zinc blende is roasted to be converted into zinc oxide. Zinc spar is put under calcination to be converted into zinc oxide.
$$2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2$$
$$ZnCO_3 \rightarrow ZnO + CO_2$$
Zinc oxide so obtained is reduced to zinc metal by heating with carbon (a reducing agent).
$$ZnO + C \rightarrow Zn + CO$$

Answer the following questions:
Out of $$PbS$$ and $$PbCO_{3}$$ (ores of lead), which one is concentrated by froth floatation process preferably?

$$ PbS $$ is concentrated by froth floatation process preferably. It is generally used for removing gangue from sulphide ores

State two important uses of following metals:
Uses of copper.

$$ \bullet \,\, $$ It is used for making electric transmission wires.

$$ \bullet \,\, $$ It is used for making utensils.

What is the role of cryolite $$(Na_{3}AlF_{6})$$ in the electrolytic reduction of alumina in Hall's process?

The role of cryolite in the electrolytic reduction of alumina in Hall's process is:

a. Lowers the fusion temperature from $$2050^{\circ}C$$ to $$950^{\circ}C$$.

b. Increases its conductivity since pure alumina is almost a non-conductor of electricity.

c. Cryolite acts as a solvent for the electrolytic mixture.

Give reason :
Copper is used in making electric cables.

Copper is ductile and a very good conductor of heat and electricity. This is the reason that copper is used in making electric cables.

Give reason:
Aluminium is used in making aircrafts.

Aluminum is used in making aircraft because it is light and strong. It is mixed with other metals to make stronger alloys.

Why does iron or zinc not occur free in nature?

Iron and zinc are quite reactive and hence they do not occur in the free state. The compounds of metals found in nature are their oxides, carbonate and sulphides.

Give the principles of hydraulic washing.

The difference in the densities of the ore and the gangue is the main criterion of hydraulic washing.

Name an ore which is concentrated by:
(a) forth floatation process
(b) magnetic separation

(a) Froth flotation process: Zinc blende (ZnS)
(b) Magnetic Separation: Haematite $$(Fe_{2}O_{3})$$

Answer the following:
(a) Name the process by which the refining of aluminium is done.
(b) Where are the cathode and anode in the electrolytic cell? Name the material used for these.
(c) State the reactions at the electrodes.

(a) The process by which refining of aluminium is done is called Hoop's electrolytic process.
(b) Molten impure aluminium forms the bottom layer. The bottom layer has carbon lining and serves as anode.
Pure molten aluminium with carbon electrodes serves as cathode in top layer.
(c) Reactions at the two electrodes are:

Anode: $$ Al - 3e^{-} \rightarrow Al^{3+}$$
Cathode: $$ Al^{3+} + 3e^{-} \rightarrow Al$$

Give the principle of froth floatation.

This process depends on the preferential wettability of the ore with oil and the gangue particles by water.

State two important uses of following metals:
Uses of aluminium.

$$ \bullet \,\, $$ Aluminium foils are used for packing foodstuff, medicines, etc.

$$ \bullet \,\, $$ It is used for making high voltage electric transmission wires.

In order to obtain 1 tonne of aluminium, 4 tonnes of bauxite, 150 kg of sodium hydroxide and 600 kg of graphite is required. The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (III) oxide, Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite.
When bauxite is treated with sodium hydroxide solution, what happens to
(i) the aluminium oxide
(ii) the iron (III) oxide

(i) The aluminium oxide forms sodium aluminate.

$$Al_{2}O_{3}.2H_{2}O + 2NaOH \overset{150^{\circ}C - 200^{\circ}C}{\rightarrow} 2NaAlO_{2} + 3H_{2}O$$

(ii) The iron (III) oxides does not dissolve in $$NaOH$$ and is removed by filtration.

Aluminium is extracted from its chief ore, bauxite. The ore is first purified and then the metal is extracted from it by electrolytic reduction.
Write equations for the reactions which takes place at the anode during the extraction of aluminium by the electrolytic process.

Reaction at anode:
$$6O^{-2} - 12e^{-} \rightarrow 6[O]$$
$$ 3O + 3O \rightarrow 3O_{2}$$

Anode is oxidized to carbon monoxide and then to carbon dioxide.
$$ 2C + O_{2} \rightarrow 2CO$$
$$ 2CO + O_{2} \rightarrow 2CO_{2}$$

Aluminium is extracted from its chief ore, bauxite. The ore is first purified and then the metal is extracted from it by electrolytic reduction.
Mention one reason for the use of aluminium in thermite welding.

In Aluminium thermite welding, the reduction with aluminium is highly exothermic and heat generated is sufficient to melt the metal.

$$ Fe_{2}O_{3} + 2Al \rightarrow 2Fe + Al_2O_{3}+$$ $$Heat$$

In order to obtain 1 tonne of aluminium, 4 tonnes of bauxite, 150 kg of sodium hydroxide and 600 kg of graphite is required. The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (III) oxide, Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite.
In construction work, why is the alloy of aluminium(duralumin) used rather than pure aluminium?

In construction, the alloy of aluminium(duralumin) is used because it is hard and resistant to corrosion.

Give reasons why aluminium is used in:
(a) making alloys
(b) wrapping chocolates
(c) painting electric and telegraphic poles
(d) aluminothermy
(e) making ships

(a) Aluminium being strong, light and corrosion resistant metal is used for making alloy.
(b) Aluminium is light, malleable and does not rust so it is used for wrapping chocolates.
(c) To prevent them from rusting.
(d) It is used in aluminothermy as it is a good reducing agent.
(e) As aluminium forms a film of aluminium oxide, it protects the ships from corrosion. So it is used for making ships.

Explain the significance of graphite in the extraction of aluminium.

Graphite acts as cathode as well as anode.

In order to obtain 1 tonne of aluminium, 4 tonnes of bauxite, 150 kg of sodium hydroxide and 600 kg of graphite is required. The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (III) oxide, Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite.
(i) Write the formulae of cryolite.
(ii) Write down the word which correctly completes the following sentence.
By dissolving aluminium oxide in cryolite a ____ (conducting/ non conducting) solution is produced.
(iii) Why is so much graphic required for the electrolytic process?
(iv) Write the equation for the reaction which takes place at cathode.

(i) The formula of the cryolite is $$Na_{3}AlF_{6}$$.
(ii) Conducting
(iii) In electrolytic process, the graphite acts as anode. The anode has to be replaced from time to time as it gets oxidized by the oxygen evolved at the anode.
(iv) The reaction that occurs at cathode is:

$$ Al^{3+} + 3e^{-} \rightarrow Al$$

Explain the term Gangue.

Gangue is the unwanted impurities like rock material, dust, soil, sand, earthy particles, limestone, mica, etc. present in an ore.

Aluminium is used in thermite welding.
(a) What is thermit?
(b) What is ignition mixture?
(c) Write the reaction for the process.

(a) A mixture of 3 parts of ferric oxide $$(Fe_{2}O_{3})$$ and one part of aluminium powder (Al).

(b) A mixture of potassium chlorate and magnesium powder is the ignition mixture.

Aluminium is extracted from its chief ore, bauxite. The ore is first purified and then the metal is extracted from it by electrolytic reduction.
Name a chemical used for dissolving aluminium oxide. In which state of subdivision is the chemical used?

Fluorspar and cryolite are used for dissolving $$Al_{2}O_{3}$$. This chemical is used in the middle state.

Write chemical equation for the event.
Zinc oxide is dissolved in dilute hydrochloric acid.

chemical equation for the event:

Zinc oxide is dissolved in dilute hydrochloric acid. is $$ZnO + HCl \rightarrow ZnCl_2 + H_2O$$

Write scientific reason.
Pine oil is used in froth flotation.

Pine oil is added in the froth flotation method to create froth or bubble so that metal can be purified easily because pine oil prevents the ore from gangue for further mixing. Pine oil also acts as the best substance for forming froth for the minerals. It also increases the non-wettability of mineral particles.

Column - I and Column II contain four entries. Entries of column I- are to be matched with some entries of column-II. Each entry of column-I may have the matching one or more than one entries of Column- II

Metal which occur in the native state in nature is Ag
The oxides of metal that can be commercially reduced by Aluminothermic reduction process is Cr
Van Arkel method is used for preparing ultrapure metal of Ti
Auto reduction process is employed for the sulphide ore of Hg

State briefly the principles which serve as basis for the following operation in metallurgist.
Refining by liquation

In refining by liquation method, a low melting metal like tin can be made to flow on sloping surface. In this way, it is separated from higher melting impurities.

State briefly the principles which serve as basis for the following operation in metallurgist.
Froth floatation process.

The principle of froth floatation is that the mineral particles are wetted by oils and gangues particles by water.

State briefly the principles which serve as basis for the following operation in metallurgist.
Zone refining.

Zone refining is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal.

There are several methods for refining of crude metals:
Explain liquation.

The impure metal is heated in the sloping floor. The low melting metal melts and flows down leaving behind the impurities. Thus method is known as liquation.

Why copper wire is use for wiring at our houses? Explain.

$$\text{Copper}$$ is $$\text{very good conductor}$$ of $$electricity$$. Electricity flows through it very easily. $$\text{It conducts electricity evenly in all circuits of house wiring}$$, so $$\text{copper is used for electrical wiring in houses.}$$

From the figure, give the electrode reaction. What is this process called ?

This process is known as electrolyte refining. The impure metal is used as anode and pure metal is used as cathode. The electrolyte is a solution of a suitable salt of the metal. On passing electric current, the pure metal is deposited on the cathode. The solid impurities fall to the bottom of the cell and are recovered as anode mud. The soluble impurities go to the solution. For the purification of copper sulphate and the electrode reactions are
Anode: $$Cu \rightarrow Cu^{2} + 2e^{-}$$
Cathode: $$Cu_{2} + 2e^{-} \rightarrow Cu$$

Outline the principles of refining of metals by the following method:
Zone refining.

1. This method is based on the principle that the impurities are more soluble in the molten state of metal (the melt) than in the solid state. In the process of zone refining, a circular mobile heater is fixed at one end of a rod of impure metal. As the heater moves the molten zone of the rod also moves with it. As a result pure metal crystallizes out of the melt and the impurities pass onto the adjacent molten zone. This process is repeated several times, which leads to segregation of impurities at one end of the rod. Then the end with impurities is cut off. Silicon, boron, gallium, indium etc can be purified by this process.

2. Column chromatography is a technique used to separated components of mixture where components are in minute quantities. In chromatography there are two phases: mobile phase and stationary phase. The stationary phase is immobile and immiscible. $$Al_2O_3$$ column is usually used as the stationary phase in column chromatography. The moblie phase may be a gas, liquid or super critical fluid in which the sample extracts dissolves. Then the mobile phase is forced to wave through stationary phase. The component that is more strongly absorbed on the column takes a longer time to travel than the component weakly absorbed.

The reaction, $$Cr_2O_3 + 2Al \rightarrow Al_2O_3 + 2Cr (\Delta \epsilon P = -421 \,KJ)$$ is thermo dynamically feasible as is apparent from the Gibbs energy value. Why does it not take place at room temperature ?

Since $$\Delta G$$ is negative, the reaction is feasible. But certain amount of activation energy is required for this reaction to occur and hence it will not take place at room temperature (heating is required).

Explain the terms gauge, Flux and slag in metallurgy.

Generally ores are contaminated with earthy, impurities and these impurities are called gauge or substance added is called flux. The flux combines with the impurities present in the ore to form an easily fusible material called slag.

List out some metals which occur free in nature.

Gold, silver and platinum.

Write two uses of borane and aluminium.

Uses of Borane

It is used as a reducing agent in organic reactions.
It is used as a fuel for supersonic rockets.

Uses of Aluminium

It is used in packing of materials.
It is used in making utensils.

There are several methods for refining of crude metals:
What is the principle of zone refining ?

This method is based on the principle that the impurities are more soluble in molten state. The impure metal, in the form of a rod, is melted over a very narrow region at one end. The impurities get accumulated in the molten region and the molted region is gradually transferred to one end by moving the heat source. The impurities collected in the molten region are swept at one end of the metal and are discarded.

Write chemical reaction of reduction of metal chromium oxide in alumino thermite process.

$$Cr_{2}O_{3} + 2Al\underset {Thermalreduction}{\rightarrow} 2Cr + Al_{2}O_{3}$$.

Draw labelled figure of zone refining process. Where this process is widely used?

Semiconductors like silicon $$(Si)$$ and germenium $$(Ge)$$ are required in high grade of purity. These metals are extracted by this process. This method is based on the principle that the impurities are more soluble in the molten form than in solid state of metal. On cooling pure metal recrystalises out of the melt while impurities remain in the form of melt in molten zone.
1743064_1831304_ans_b988d5d6525a46ad85bf3e0604872953.png

1743064_1831304_ans_b988d5d6525a46ad85bf3e0604872953.png

Explain thermodynamic principle in : reduction of haematite ore from Elligham diagram.

According to Ellingham diagram:
1. Temperature $$1073\ K$$ represents intersection point.
2. Reduction of haematite below $$1073\ K$$ is done by carbon monoxide. Hence
$$\triangle G^{\circ} (Fe \rightarrow Fe_{2}O_{3}) > \triangle G^{\circ} (CO \rightarrow CO_{2})$$
Reaction completes in following way:
$$Fe_{2}O_{2(s)} + 3C_{(g)} \xrightarrow {< 1073\ k} 2Fe_{(s)} + 3CO_{2(g)}$$
3. Reduction of haematite above $$1073\ K$$ is done by coke (or carbon). Hence
$$\triangle G^{\circ} (Fe\rightarrow Fe_{2}O_{3}) > \triangle G^{\circ} (C \rightarrow CO)$$
In this way reduction is as follows:
$$Fe_{2}O_{3(s)} + C_{(s)} \xrightarrow {Temp > 1073\ k} 2Fe_{(s)} + 3CO_{(g)}$$.
1743070_1831320_ans_defe15ee2f9d4cf489170b0bddaa4a33.png

1743070_1831320_ans_defe15ee2f9d4cf489170b0bddaa4a33.png

Give example of following steps used in froth floatation method:
(i) Frothing agent
(ii) Collector/ Floating agent
(iii) Forth stabilizers
(iv) Activator
(v) Depressant or depresser.

(i) Frothing Agent :
Examples:
Mainly fatty acid, pine oil and eucalyptus oil are good frothing agent.
(ii) Collector/ Floating Agent:
Main floating agent is sodium ethyl xanthate.
(iii) Stabilizers:
Examples : Cresol and aniline
(iv) Activator:
Example : Copper sulphate $$(CuSO_{4})$$
(v) Depressant :
Example:
Sodium cyanide $$(NaCN)$$, Base $$(Na_{2}CO_{3})$$.

What is difference between mineral and ore. Explain it.

The naturally occurring chemical substance in which metal occurs in the earth's crust is called mineral. On the other hand, the mineral from which metal can be economically and conveniently extracted is called an ore.

Write name of any two metals which are found in native state.

$$Ag$$ and $$Au$$.

Write name and role of collectors and froth stabilizers in froth floatation method.

(i) Floatation Agent (Collectors):
These substances make the suphide particles water repelling. So that the particles can float on the surface of water. Main floatation agent is sodium ethyl xenthate.
$$RO - \underset {\underset {S}{parallel}}{C} - S - Na$$
$$R =$$ Ethyl or Alkyl group
(ii) Froth stabilizers:
They provide stability to froth. For example.
1743056_1831246_ans_5357b76b2d5e4516bce5ae3b32771b1f.png

1743056_1831246_ans_5357b76b2d5e4516bce5ae3b32771b1f.png

Write chemical reaction of Hall-Heroult process of bauxite ore and draw labelled diagram of electrolytic cell.

Following two concepts are there for the reaction taking place during electrolysis:
1. According to the first concept which is most famous, ionisation of alumina occurs firstly:
At cathode $$\begin{Bmatrix} \underset {Molten}{Al_{2}O_{3}}& \xrightarrow {Electrolysis} 2Al^{3+} + 3O^{2-}\\ Al^{3} + 3e^{-} & \rightarrow Al(l) \end{Bmatrix}$$
At anode $$\begin{Bmatrix}O^{2-} & \rightarrow & O + 2e\\ O + O & \rightarrow & O_{2} \\ 4C + 3O_{2} & \rightarrow & 2CO + 2CO_{2}\end{Bmatrix}$$
$$2C + O_{2} \rightarrow 2CO$$
$$2CO + O_{2} \rightarrow 2CO_{2}$$
Hence, corrosion of graphite rods (anode) occurs and they have to be replaced periodically. For $$1\ kg$$ of aluminium produced about $$0.5\ kg$$ of anode (graphite) is consumed.
2. According to the second concept, ionisation of 'Cryolite' occurs firstly on passing electric current.
$$\underset {Molten\ cryolite}{Na_{3}AlF_{6}}\overset {Electrolysis}{\rightleftharpoons} 3NaF + AlF_{3}$$
$$AlF_{3} \overset {Electrolysis}{\rightleftharpoons} Al^{3+} + 3F^{-}$$
At cathode : $$Al^{3+} + 3e^{-} \rightarrow Al_{(l)}$$
At anode : $$F^{-} \rightarrow F + e^{-}$$
$$3C + 2Al_{2}O_{3} \rightarrow 4Al + 3CO_{2}$$
At anode, $$Al_{2}O_{3}$$ is changed into $$AlF_{3}$$ and the process of electrolysis continuously goes on when $$Al_{2}O_{3}$$ is again ionised.
The whole reaction may be written in the following way:
$$2Al_{2}O_{3} + 3C \rightarrow 4Al + 3CO$$
Molten aluminium thus obtained is collected at the bottom of cell which is taken out with the help of tap.
The aluminium metal obtained by this method is about $$99.5\%$$ pure. The complete process is known as electrometallurgy.
1743079_1831345_ans_8df02bb76158485a93260702e32a991e.png

1743079_1831345_ans_8df02bb76158485a93260702e32a991e.png

Nature of some ores are given. Pick ore concentration from the bracket.
(Magnetic Separation , Froth Floatation , Levigation , Leaching)
Ores are lighter and impurities are heavier.

Froth Floatation method is used as concentration when ores are lighter and impurities are heavier.

Which reducing agent is good among $$C$$ and $$CO$$ at low temperature range in blast furnance to obtain iron form iron oxide and why?

At lower temperature range, both $$C$$ and $$CO$$ act as reducing agent but in comparison with $$C, CO$$ easily oxidises to $$CO_{2}$$. Therefore at lower temperature range $$(Temp < 1073), CO$$ acts as better reducing agent than carbon.

Write short notes on following:
(i) Gangue/ Matrix
(ii) Slag
(iii) Flux.

(i) Gangue/ Matrix
The unwanted earthy and silicious impurities e.g. sand, clay, rock etc. associated with the ore is called gangue or matrix.
(ii) and (iii) Slag and Flux:
Flux is a substance which combines with gangue which may still be present in the calcined or roasted ore to form an easily fusible material called the slag.
$$Flux + Gangue \rightarrow Slag (fusible)$$.

To which electrodes does $$ Al^{3+} $$ move ?

$$\mathrm{Al^{+3}}$$ being a cation moves toward negative electrode i.e. cathode.

Purification of copper is depicted here.
Identify the anode , cathode and electrolyte.

Anode, Cathode, and electrolytes in the process of purification of copper are:

Anode: Impure copper

Cathode: Pure copper

Electrolyte: Aqueous solution of $$ CuSO_4$$ to which $$ H_2SO_4$$ is added.

What are gangue, flux, and slag?

Gangue: Impurities in the metal ore are called gangue.

Flux: Chemical substances used to convert impurities which are not easily removable (gangue) into slag.

Slag: Substance which are easily removable when gangue and flux are combined.

Copper is used for making wires. Which property of copper is used in making wires?

The property which is used in making wires of copper is ductility.

Which ores are concentrated by froth flotation process. Write in brief description and draw labelled diagram.

This process is generally used for the concentration of sulphide ores.
For example:
Copper pyrite $$(CuFeS_{2}), Galena [PbS]$$, Zinc Blende $$(Zn)$$ etc.
Method:
Water is taken in a big rectangular utensil. In this, powdered ore is mixed and suspension is made. A very small quantity of floatation agents are added. The water is agitated by the blast or air.
Due to which, light particles of sulphide ore carried out to the surface by the foam and from there they are skimmed off. The gangue particles are preferentially wetted by water sinks to the bottom of the tank.
1743025_1831425_ans_e2a0b58ed61c4909913232ec7c6b786b.png

1743025_1831425_ans_e2a0b58ed61c4909913232ec7c6b786b.png

Why is froth-floatation used as the method of concentration for copper-pyrites ore?

Copper pyrites have a lesser density and impurities have higher density. Also, only the ore particles float in pine oil. So, the method of concentration used for copper-pyrites ore is froth-floatation.

What is the refining method used for the refining of copper?

Electrolysis is the refining method used for the refining of copper.

What is the refining method used for the refining of Mercury?

Distillation is the method used for the refining of Mercury.

What is meant by stabilizer? Give example.

The soft drinks available in market do not settle down even after prolonged storage. To retain as such for long time without settling down some chemicals are added to it. These are called stabilizers.
Eg. Brominated vegetable oil.

Element with strongest reducing nature is:

Element with strongest reducing nature is Lithium.

How does $$NaCN$$ act as a depresent in preventing $$ZnS$$ forming the froth?

$$NaCN$$ combines with $$ZnS$$ to form a complex, $$Na_2 [Zn(CN)_4]$$ on the surface of $$ZnS$$ and thus prevents it form forming the froth
$$ZnS+4\ NaCN\to Na_2[Zn(CN)_4]+Na_2S$$

In general which metals do you expect to occur in the native state in nature? Give examples.

Metals are as $$Cu, Ag, Au, Pt$$ etc, which lie below hydrogen in electrochemical series are not readily attracted by oxygen, moisture and $$CO_2$$ of the atmosphere and hence occur in the native salts in nature.

Which method would you suggest for the separation of the metals is in the following mixture?
$$Zn$$ from iron
Give a reason for your choice.

$$Zn\ (b.p. 1180\ K)$$ can be easily separated from iron $$(b.p. 3273\ K)$$ by distillation.

Copper and silver lie below in the electrochemical series and yet they are found in the combined state as sulphide in nature. Comment.

As explained in $$Q.3$$ due to high polarising power of their sulphides are even more stable than the metals.

Why do some metals occur in the native state?

Metals like $$Au$$ and $$Pt$$, which are not reactive, i.e. are not attacked by $$O_2$$ moisture and $$CO_2$$ of the air occur in the native state.

What is a depressant. Give one example.

Compounds which prevent the formation of froth in froth-flotation process are called depressants. For example $$NaCN$$, can be used as a depressant for $$ZnS$$ in the separation of $$ZnS$$ ore from $$PbS$$ ore. It forms a layer of zinc complex, $$Na_2 [Zn(CN)_4]$$ on the surface of $$ZnS$$ and thus prevents it from forming the froth.

What is the role of a stabilizer in froth-floatation process?

Chemical compounds like cresols and aniline which tend to stabilize the froth are called froth stabilizers.

Give the chemical formula of Bauxite

$$Al_2O_3.2H_2O$$

Give the appropriate term defined by the statements given below:
The process by which certain ores, specially carbonates, are converted to oxides in the absence of air.

Calcination

Calcinaton involves heating when the volatile matter escapes leaving behind the metal oxide.

$$ZnCO_3\xrightarrow{\Delta} ZnO +CO_2$$

Match the conversions in List 1 with the type(s) of reaction(s) given in ListIndicate your answer by darkening the appropriate bubbles of the $$4 \times 4$$ matrix given in the ORS.

Roasting is a step of the processing of certain ores. It is a metallurgical process involving gas–solid reactions at elevated temperatures with the goal of purifying the metal component(s).

$$2 PbS + 3 O_2\rightarrow 2 PbO + 2 SO_2$$

Calcination is also used to mean a thermal treatment process in the absence or limited supply of air or oxygen applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction.

$$CaCO_3\rightarrow CaO+CO_2$$

Extraction
(1) Zinc blende is heated in air to get rid of the Sulphur and to convert it into ZnO which is more reactive. This way, it will be easier to obtain the zinc metal.
Reaction when Zinc Blende is heated in the air:

$$2 ZnS + 3 O_2\rightarrow 2 ZnO + 2 SO_2$$

(2) The Zinc Oxide is then mixed with crushed coke (carbon) and heated at 1673 K in fire clay retorts (Belgian Process) when ZnO gets reduced to metallic zinc. In this reaction, carbon acts as the reducing agent as Zinc's oxidation state is reduced from +2 to 0 and carbon itself is reduced.

Reaction when Zinc Oxide is heated in fire clay retorts:

$$2 ZnO + C\rightarrow 2 Zn + CO_2$$

Self reduction process: This process is also called autoreduction process or air reduction process. The sulphide ores of less electropositive metals like Hg, Pb, Cu etc., are heated in air as to convert part of the ore into oxide or sulphate which then reacts with the remaining sulphide ore to give the metal and sulphur dioxide. No external reducing agent is used in this process.

$$2 Cu_2S + 3O_2\rightarrow Cu_2O + 2SO_2$$

Hence, $$A-1:B-2:C-1,3:D-1,4$$

How much approx aluminium in g can be produced by a current of 94 A flowing through a Hall-Heroult cell for 1.00h?
(If the answer is $$X$$, then write $$\dfrac X8$$)

$$Al^{3+}\,+\,3e^{-} \,\rightarrow\,Al$$

$$W = z\times i\times t$$,

Where, z = electrochemical equivalent =$$\displaystyle \frac{atomic\, mass}{electrons\,\times\,96500}\,=\,\frac{27}{3\,\times\,96500}$$

$$i = current (A) = 94.0\,A\quad\\ t = time (seconds) = 1 h = 3600 s$$

$$\displaystyle \therefore\, w\,=\,\frac{9\,\times\,94\,\times\,3600}{96500} = 31.56 g\approx 32\ g$$

$$\therefore \cfrac {X}{8} = \cfrac {32}{8} = 4$$

State whether the given statement is True or False.
$$CuO$$ can't be reduced by carbon but it can be reduced by $$H_2$$.
given : $$\Delta G^{\circ}_{f}$$ for $$CuO =$$ -129.7 kJ $$mol^{-1}$$, $$CO =$$ - 137.2 kJ $$mol^{-1}$$ $$H_2O$$ = - 237.2 kJ $$mol^{1}$$

$$CuO+C \rightarrow Cu+CO$$

$$ΔG^∘=ΔG^∘_f(CO)−ΔG^∘_f(CuO)$$

$$= - 137.2 + 129.7= - 7.5 kJ$$

$$CuO+H_2\rightarrow Cu+H_2O$$

$$ΔG^∘=ΔG^∘_f(H_2O)−ΔG^∘_f(CuO)$$

$$= - 237.2 + 129.7= - 366.9 kJ$$

Both the reactions are spontaneous means $$CuO$$ can be reduced by both $$C$$ and $$H_2$$ and thus the given statement is $$False.$$

Out of $$C$$ and $$CO$$, which is a better reducing agent at $$673 K$$?

At $$673\ K$$, the $$\displaystyle \Delta G^o$$ vs $$T$$ line for $$CO$$, $$\displaystyle CO_2$$ is lower than that of $$C,\ CO$$ line. Hence, $$CO$$ can be used as better reducing agent than $$C$$ at $$673\ K$$.

Name the common elements present in the anode mud in electrolytic refining of copper. Why are they present?

In the electrolytic refining of copper, the anode mud contains antimony, selenium, tellurium, silver gold and platinum. These are impurities in blister copper. They are less reactive and unaffected by $$\displaystyle CuSO_4 - H_2SO_4 $$ solution and hence, settle down under anode as anode mud.

Predict conditions under which $$Al$$ might be expected to reduce $$MgO$$.

Below $$1350^{\circ}C,\ Mg$$ can reduce $$Al_{2}O_{3}$$ and above $$1350^{\circ} C$$, $$Al$$ can reduce $$MgO$$. This can be inferred from $$\Delta G^{\ominus} Vs\ T$$ plots.
$$\Delta G^{\ominus} Vs\ T$$ plot for $$Mg$$, $$MgO$$ is below $$\Delta G^{\ominus} Vs\ T$$ plot for Al. At the point of intersection ( corresponding to $$1350^{\circ} C$$), $$\Delta G^{\ominus}$$ for combined reaction is zero. After $$1350^{\circ} C$$, Mg, MgO curve is higher than Al $$Al_2O_3$$ curve. There are practical difficulties to attain higher temperature.

Write chemical reactions taking place in the extraction of zinc from zinc blende.

During extraction of Zn from zinc blende (ZnS), following reactions occur:
(i) ZnS is roasted in excess air at $$1200$$ K to form ZnO.

$$\displaystyle 2ZnS + 2O_2 \xrightarrow {\Delta} 2ZnO + 2SO_2$$
(ii) ZnO is heated with crushed coke at $$1673$$ K, where it is reduced to Zn.
$$\displaystyle ZnO + C \xrightarrow {1676 \: K} Zn + CO$$
(iii) Electrorefining is carried out for refining of impure zinc. Anode is impure zinc and cathode is pure zinc. Electrolyte is a mixture of zinc sulphate and dilute sulphuric acid (small amount). When current is passed, zinc is deposited on cathode and is collected.
At anode : $$\displaystyle Zn \rightarrow Zn^{2+} + 2e^-$$
At cathode: $$\displaystyle Zn^{2+} +2e^- \rightarrow Zn$$

What is the role of cryolite in the metallurgy of aluminium?

Before electrolysis, cryolite is added to bauxite ore because of the following reasons.
(1) It acts as a solvent.
(2) It decreases the melting temperature of alumina to $$1173$$ K.
(3) It increases the electrical conductivity.

Why is zinc not extracted from zinc oxide through reduction using $$CO?$$

Zinc is not extracted from zinc oxide through reduction using CO.
Reducing agent should have more negative $$\displaystyle \Delta G$$ value. However in present case, Zn has more negative $$\displaystyle \Delta G$$ value then CO, so it can not be reduced by CO.

Outline the principles of refining of metals by the following methods:
(i) Zone refining
(ii) Electrolytic refining
(iii) Vapour phase refining

(i) Zone refining
It is used for refining $$Si, B, Ga, In$$ etc. Impurities are more soluble in the molten state of metal than in solid state. There is a circular mobile heater at one end of a rod of impure metal. Heater and the molten zone moves from one end to another end. Pure metal crystallizes out of the melt and the impurities pass onto the adjacent molten zone. Repetition of this process several times segregates impurities at one end of a rod. The end with impurities can then be cut off.

(ii) Electrolytic refining
It is carried out for refining of impure zinc. The anode is impure zinc and cathode is pure zinc. The electrolyte is a mixture of zinc sulphate and dilute sulphuric acid (small amount). When current is passed, zinc is deposited on the cathode and is collected.
At anode : $$\displaystyle Zn \rightarrow Zn^{2+} + 2e^-$$
At cathode: $$\displaystyle Zn^{2+} +2e^- \rightarrow Zn$$

(iii) Vapour phase refining
Metal is converted into volatile compound and then decomposed to obtain pure metal. This method is used for refining $$Ni, Zr$$ and $$Ti$$.
$$Ni$$ is heated with $$CO$$ to form volatile nickel tetracarbonyl.
$$\displaystyle Ni +4CO \xrightarrow {330-350 K} Ni(CO)_4$$
At high temperature, nickel tetracarbonyl decomposes to pure Ni.
$$\displaystyle Ni(CO)_4 \xrightarrow {450-470K} Ni + 4CO$$
This is Mond's process for refining Ni.

Relate all the four columns of the table with u
Metal
Ore
Chemical formula
Reduction process
Al
haemetite
$$PbS$$
blast furnace
Cu
bauxite
$$Fe_2O_3$$
bessemerisation
Fe
copper pyrite
$$Al_2O_2H_2O$$
froth floatation
Pb
galena
$$CuFeS_2$$
Hall's process

Metal	Ore	Chemical Formula	Reduction Process
$$Al$$	Bauxite	$$Al_2O_3\cdot 2H_2O$$	Hall's process
$$Cu$$	Copper pyrite	$$CuFeS_2$$	Bessemerisation
$$Fe$$	Haemetite	$$Fe_2O_3$$	Blast Furnace
$$Pb$$	Galena	$$PbS$$	Froth Floatation

In the extraction of aluminium ;
(i) name the process of concentration of bauxite.
(ii) write the cathode reaction in electrolytic reduction of alumina.
(iii) write the function and chemical formula of cryolite.
(iv) write a chemical equation for the action of heat on aluminium hydroxide.
(v) why is it necessary to replace anodes time to time?

(i) The concentration of ore is done by Baeyer's process using chemical method.

(ii) The electrolytic reduction of alumina is done by Hall Heroult's process. The reaction at cathode is : $$ Al^{3+} + 3e^{-} \rightarrow Al$$

Thus, pure aluminium metal is formed at the cathode.

(iii) Cryolite is sodium aluminium fluoride ($$Na_3AlF_6$$). It is an ore of aluminium. Cryolite and fluorspar are added to the molten mixture of alumina to reduce the melting point and increase the electrical conductivity.

(iv) $$2Al(OH)_3 \rightarrow Al_2O_3 + 3H_2O $$

(v) The oxygen evolved at the anode escapes as gas or reacts with the carbon anode. The anode is thus oxidized to carbon monoxide which either burns giving $$CO_2$$ or escapes. Thus, anode has to be replaced as it is consumed periodically.

Explain Hall-Heroult method of obtained pure aluminium from alumina with figure.

The method to obtain aluminium from alumina by the electrochemical method was invented by Charles Hall and Paul Héroult.
Electric current cannot pass through the solid form of alumina, and the melting point of alumina is also very high. Hence, cryolite is added to alumina in a small amount to carry out electrolysis easily.
This mixture acts as a good conductor of electricity. Addition of feldspar also lowers the melting point of alumina. Thus, a mixture of alumina, cryolite and feldspar is subjected to electrolysis to obtain pure aluminium.
For electrolysis, an iron vessel with an inner layer coated with carbon-layered graphite is used. This acts as a cathode.
The carbon rods are joined with a copper clamp and immersed in an electrolyte. These rods act as the anode.
On passing electric current, molten aluminium is deposited at the cathode and oxygen gas is released at the anode.

At the cathode : $$2Al^{3+} (l)+6e^- \rightarrow 2Al(l)$$

At anode : $$6O^{2-}(l) \rightarrow 6O_2(g)+12e^-$$

In which furnace the smelting is done?

Smelting is a process of heating ores of various metals such as copper glance ($$Cu_2S$$) in the presence of oxygen (for oxidation) or coke (for reduction) at temperatures beyond the melting point of metals. It is done in a reverberatory furnace.

Answer the following questions with respect to the electrolytic process in the extraction of aluminium:
Explain why powdered coke is sprinkled over the elecrolytic mixture.

The molten electrolyte is covered with layer of powder coke to prevent oxidation and loss of heat due to radiation.
Note:
With respect to the electrolytic process in the extraction of aluminium, the components of the electrolyte other than pure alumina $$ \displaystyle ( Al_2O_3) $$ (2-8%) are synthetic cryolite $$ \displaystyle (Na_3AlF_6)$$ (80-85%), $$ \displaystyle AlF_3$$ (5-7%) and fluorspar $$ \displaystyle (CaF_2 )$$ (5-7%).
The addition of cryolite and fluorspar not only makes alumina a good comductor of electricity but also lowers the fusion temperature to around 1140 K.

Draw a neat and labelled diagram of zone refining process.

A neat and labelled diagram of zone refining process is as shown below.

Generally which ores are concentrated by froth floatation method? Describe this method.

Sulphide ores (such as galena ($$PbS$$), zinc blende ($$ZnS$$) and copper pyrites $$(CuFeS_2)$$ are concentrated by froth flotation method.
Principle: Metal sulphide particles (of ore) are selectively wetted by oil. Gangue particles are wetted by water.
Finely divided ore is added to water (present in a large tank). Pine oil, eucalyptus oil, xanthates or fatty acids are added. Compressed air is circulated.
Metal sulphide particles (of ore) are selectively wetted by oil. They (and froth) rise to surface. Gangue particles are wetted by water. They settle at the bottom.

Describe the extraction of Mercury metal from its ore Cinnabar $$(HgS)$$.

Cinnabar (ore of mercury) means HgS (mercury sulphide).

Concentration of ore - this involves grinding of her and separating the unwanted dirt from it.
Roasting of ore - as the ore is of sulphide then roasting is to be done this involves the heating of sulphide ore in the Presence of oxygen to form metal oxide and Sulphur dioxide. HgS + O2 - HgO + SO2.
Further heating - as Mercury is a low reactive metal hence we can heat it’s oxide to separate them. Means 2HgO+ heat - 2Hg + O2.
Now the Mercury contains some chemical impurities which can be separated by the process electrolyte refining and hands then the Mercury will now the Mercury contains some chemical impurities which can be separated by the process electrolyte refining and then the Mercury will be separated from its Ore cinnabar.

The oil used as frothing agent in froth floatation process is ?

It is a process for seperating hydrophobic material from hydrophilic. Froth Flotation method is use during processing of minerals, recycling of paper, in mining industry and in waste water treatment industries. It checks if the material is water repelling or having affinity for water. The overall concept is based on density and the nature of material. $$\text {The oil used in froth flotation process in pine oil}$$, it is because it does not have affinity towards water and it easily attracts impurities and impurities can easily wash away.

A tetravalent element forms monoxide and dioxide with oxygen. When air is passed over heated element $$\left(1273\ K\right)$$, producer gas is obtained. Monoxide of the element is a powerful reducing agent and reduces ferric oxide to iron. Identify the element and write formulas of its monoxide and dioxide. Write chemical equation for the formation of producer gas and reduction of ferric oxide with the monoxide.

1872170_1338431_ans_6da7b5bbadda4ae9a8b5722189f6b7a5.jpeg

Draw the diagram showing i) Froth floatation ii) Magnetic separation. $$\left( { AS }_{ 5 } \right) $$

2047289_1393491_ans_e243d2f218a64131b8b2384921e197f3.jpeg

Define the term 'metallurgy'. State the processes involved in metallurgy.

1881291_1540767_ans_b3f8fe7f81c94b248735c8a711d89409.jpg

Draw an Ellingham diagram for metal oxides and explain what information can be obtaines from it.In addition explain why why most of the lines slope upwards from left 10 right,why the lines change in slope, and what happens when a line crosses the $$ \Delta G = 0 $$ axis

Describe the extraction of magnesium and bromine from sea water.

Use the Ellingham diagram for oxides to find:
1. If Al will reduce chromium oxide
2. At what temperature C will reduce magnesium oxide, and
3. At what temperature mercuric oxide will decompose into its elements.

Find the number of metals from the given metals which can be commercially purified by zone refining methods.
Si, Ge, Ga, Al, Ti, Zr

Zone refining is based upon fractional crystallization as the impurity prefers to stay in the melt and on solidification only pure metals solidifies on the surface of melt.

In this process solubility of the impurities in the metal in molten and solid states is different.

Metals like Si, Ge, Ga and B of high purity are purified by this method.

This process is known as ultra-purification because it results in impurity level decreasing to ppm level.

Hence , 3 is the right answer as only three metals follow zone refining method among the given list.

Match the items of column I with items of column II and assign the correct code

A) Sapphire is a gemstone that contains $$Al_2O_3$$

Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminum oxide with trace amounts of elements such as iron, titanium, chromium, vanadium

B) Sphalerite is ore of zinc. The molecular formula of sphalerite is $$ZnS$$.

C) In the concentration of Galena $$(PbS)$$ ore, sodium cyanide is added as depressant for zinc sulphide $$(ZnS)$$.

D) Corundum is a mineral of aluminium with a molecular formula $$Al_2O_3$$.

Hence, the correct options are,

A) Sapphire - 1) $$Al_2O_3$$

B) Sphalerite - 4) $$ZnS$$

C) Depressant - 2) $$NaCN$$

D) Corundum - 1) $$Al_2O_3$$

At temperatures above 1073 K coke can be used to reduce FeO to Fe. How can you justify this reduction with Ellingham diagram?

As per Ellingham diagram at temperatures greater than 1073 K $$\Delta G (C, CO) < \Delta G (Fe, FeO)$$. Hence coke can reduce FeO to Fe.

Explain the following:
$$CO_2$$ is a better reducing agent below 710 K whereas $$CO$$ is a better reducing agent above 710 K.

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Name the following:
Two metals which are used for the reduction in metallurgical process.

1716923_1725999_ans_a59b147062424f628b9436e121ea1987.jpg

Write short note on:
Forth floatation process

1910905_1726029_ans_2d2f1648024c4f2ba015164de4e5ab0a.jpg

Match List-I with List-II:

1600287_1726905_ans_12290462c8f0408b9727e22644d51ad6.jpg

Answer the following:
What is the silver paint?

1962155_1728042_ans_87b7e04907794495bf3bf270bfb853d9.jpg

Described the thermodynamic principle of metallurgy. How the Ellingham diagram useful in predicting the feasibility of thermal reduction of a metal oxide.

1961938_1726057_ans_2a29e408f5b0412eae3e34b99814fba3.jpg

Write down the formula of the following:
Leuna saltpetre

Leuna saltpetre is a mixture of $$(NH_4)_2SO_4$$ and $$NH_4NO_3$$ salt.

Give formula of the following:

Colemanite

1680939_1729950_ans_8906b4bbe9af44e4a72d979beffb1cbe.jpg

Explain how the properties of an alloy are different from those of constituent metals.

(i) Alloys are stronger and harder than the constituent metals.
(ii) Alloys are more resistant to corrosion.
(iii) Alloys are more resistant to corrosion.
(iv) Alloys have lower electrical conductivity than pure metals.

How will you obtain mercury from cinnabar ?

Cinnabar ($$ HgS $$ -mercury (II) sulphide or mercury sulphide ) is an ore of mercury. It is heated in air to give mercuric oxide $$ (HgO) $$ . Mercuric oxide is further heated to get mercury . The reactions involved are,

$$ 2HgS (s) + 3O_2 (g) \xrightarrow{heat} 2HgO (s) + 2SO_2 (g) $$

$$ 2HgO(s) \xrightarrow{heat} 2Hg(s) + O_2(g) $$

Free energies of formation $$(\triangle_{f}G)$$ of $$MgO(s)$$ and $$CO(g)$$ at $$1273\ K$$ and $$2273\ K$$ are given below.
$$\triangle_{f}G[MgO(s)] = -941\ kJ/mol$$ at $$1273\ K\ \triangle_{f}G[MgO(s)] = -314\ kJ/mol$$ at $$2273\ K$$
$$\triangle_{f}G[CO(g)] = -439\ kJ/mol$$ at $$1273\ K\ \triangle_{f}G[CO(g)] = -628\ kJ/mol$$ at $$2273\ K$$
On the basis of above data, predict the temperature at which carbon can be used as a reducing agent for $$MgO(s)$$.

At $$1273\ K$$
$$Mg(s) + \dfrac {1}{2}O_{2}(g) \rightarrow MgO(s); \triangle_{f}G = -941\ k/mol ... (i)$$
$$C(s) + \dfrac {1}{2} O_{2}(g) \rightarrow CO(g); \triangle_{f}G = -439\ kJ/mol ... (ii)$$

Subtracting equation (i) from equation (ii), we get

$$MgO (s) + C(s) \rightarrow Mg(s) + CO(g); \triangle_{r}G = 502\ kJ/mol$$

As $$\triangle_{r}G$$ for the above reduction reaction is positive, therefore, reduction of $$MgO$$ by $$C$$ is not feasible at $$1273\ K$$.

At $$2273\ K, Mg(s) + \dfrac {1}{2}O_{2}(g) \rightarrow MgO(s); \triangle_{f}G = -314\ kJ/mol ... (iii)$$

$$C(s) + \dfrac {1}{2}O_{2}(g) \rightarrow CO(g); \triangle_{f}G = -628\ kJ/mol ... (iv)$$

Subtracting equation (iii) from equation (iv), we get

$$MgO(s) + C(s) \rightarrow Mg(s) + CO(g); \triangle_{r}G = -314\ kJ/mol$$

As $$\triangle_{r}G$$ for the above reduction reaction is $$-ve$$, therefore, reduction of $$MgO$$ by carbon at $$2273\ K$$ is feasible and hence, carbon can be used as a reducing agent.

Draw the diagram of an electrolytic cell used in the purification of Copper and label the electrode having impure copper.

$$Anode$$- Impure Copper metal rod

$$Cathode$$- Pure Copper metal rod

$$Electrolyte$$- Acidified copper sulphate solution

$$\text {Process of refining}$$ -On the application of high voltage the pure copper metal ions from the impure copper metal rod i.e. anode dissolves into the electrolyte and the same amount of $$Cu^{2+} $$ ion gets deposited over the cathode rod as shown in the diagram. Thus the impure metal can be refined by electrolytic method.

1691014_1804025_ans_f53c332c47f94d63a8ad02dae4a80169.png

How zinc is extracted from its ore?

The most commonly available ore used for zinc extraction of zinc is called zinc blende (ZnS) for concentration of ore "Froth flotation" process is used, to remove gangue from sulphide ores.

Now extract Metal from concentrated ore Roasting is used, in which sulphur content is reduced and $$ZnO$$ is formed. $$[2ZnS + 30^{2-} \rightarrow 2 ZnO + 2SO_2]$$

Now $$ZnO$$ is mixed with coke and finally reduced to pure Zinc metal.

$$2 ZnO + C \rightarrow 2Zn + CO_2 \uparrow$$

Molten cryolite is mixed Alumina in the extraction of aluminium by electrolysis. Why? Name the substances that are used as anode and cathode in this method.

Molten cryolite used as a solvent for molten alumina. It reduces the melting point of alumina and behave that electrolyte. It is mixed with molten alumina in the extraction of aluminium.

Graphite rods are used as cathode and carbon running is used as anode.

Some metals and their methods of concentration are given . Match them suitably.
Mercury , Zinc , Tin , Copper , Lead
Liquification , Electrolytic refining , Distillation

Liquation - Tin , Lead
Electrolytic refining - Copper
Distillation - Mercury , Zinc

(a) Illustrate the arrangement of refining copper and label the anode, cathode and electrolyte.
(b) Write the chemical equation at the anode and cathode and sustain it as redox reaction.

a. Refer Image

b. Anode - $$ Cu \rightarrow Cu^{2+} + 2e$$
Cathode - $$ Cu^{2+} + 2e \rightarrow Cu $$
As oxidation and reduction takes place it is a redox reaction.

1757776_1834087_ans_a7fff7ebcd014fd29689b72b995332a6.png

Purification of copper is depicted here.
Write the chemical equation during electrolysis.

The chemical reaction taking place during electrolysis are:

At anode : $$ Cu \rightarrow Cu^{2+} + 2e^- $$

At Cathode : $$ Cu^{2+} + 2e^- \rightarrow Cu $$

Purification of copper is depicted here.
What is seen below the positive electrode ?

Impurities in impure copper found below the positive electrode i.e. Anode. It is also known as anode mud.

Features of ore and impurity are given in the table. Write down the method used for the separation of the ore.
Ore Impurity Method
High density Low density (i)
Magnetic Non magnetic (ii)
Low density High density (iii)
Dissolved in
the solvent didn't dissolve (iv)

i. Levigation / Hydraulic washing
ii. Magnetic Separation
iii. Froth Floatation
iv. Leaching

What is the refining method used for the refining of Calcium?

Distillation is the method used for the refining of calcium.

Aluminium is prepared industrially by Hall-Heroult process. Various steps in the concentration of ore are given below . Write them in the correct order.
i. The precipitate formed is separated , washed and strongly heated to get alumina.
ii. Crushed bauxite is leached with hot sodium hydroxide solution.
iii. Impurities are removed from the sodium aluminate solution for filtration.
iv. Solution is diluted after adding a little aluminium hydroxide , to precipitate aluminium hydroxide.

The correct order of steps in the concentration of ore is:

(ii) Crushed bauxite is leached with hot sodium hydroxide solution.
(iii) Impurities are removed from the sodium aluminate solution for filtration.
(iv) Solution is diluted after adding a little aluminium hydroxide , to precipitate aluminium hydroxide.
(i) The precipitate formed is separated , washed and strongly heated to get alumina.

Which method can be used for separating aluminium from alumina ?

Electrolysis is used for separating aluminium from alumina.

(i) Write down the names of Anode , Cathode , Electrolyte used in the Electrolyte cell for the manufacturing of copper.
(Ii) Write down the equations for the reaction in anode and cathode.

a. Anode, Cathode and electrolyte used in the electrolysis of copper are:

Anode - Copper to be refined
Cathode - Pure Copper
Electrolyte - Aqueous Copper Sulphate Solution mixed with $$H_2SO_4$$

b. Reactions taking place at cathode and anode are:

Anode - $$ Cu \rightarrow Cu^{+2} + 2e^- $$
Cathode - $$ Cu^{2+} + 2e^- \rightarrow Cu $$

The materials like stone, rock and earthy impurities present in naturally occurring ores are known as...

The material like stone, rock, and earthy impurities present in naturally occurring ores are known as gangues. A gangue can be defined as the unwanted materials or impurities in the form of sand, rock or any other material that surrounds the mineral in an ore deposit. This substance is common when it comes to the aspect of mining. Usually, gangue has to be separated from mineral and the process used is known as mineral dressing, mineral processing or ore dressing.

Describe the principal of forth flotation process, What is the role of a stabilizer and of a depressant?
Give one example each.

Forth floatation process is based on the fact that the sulphide ore particles are only moistened with oil, whereas oxide and gangue particles are moistened by water. For, the powdered ore is mixed with water and a little pine oil and whole mixture is then stirred vigorously through rotating paddle by blowing compressed air. The oil forms a foam or forth with air. The ore particles stick to the forth and rises to the surface, while gangue are left in water. The forth is skimmed off, collected and allowed to subside to get concentrated ore.

This is especially suitable for sulphide ores.

Role of stabilizer - Stabilizers are used to stabilize the forth.

Example Cresols and aniline.

Role of depressant - Depressants are used to prevent certain type of particles from forming the froth with bubbles. Example. NaCN can le used as a depressant in the separation of ZnS and PbS.

Differentiate between the following:
Gangue and flux.

Gangue is the waste rock or materials overlying an ore or mineral body that are displaced during mining without being processed or simply rocky impurities.

Flux is any substance introduced in the smelting of ores to promote fluidity and to remove objectionable impurities.

Is carbon a satisfactory reducing agent for all metal oxides? Give reasons.

The roasted or the calcined ore is reduced to the metal by using a suitable reducing agent. The choice of the reducing agent depends on the reactivity of metal. If the metal to be extracted, is very reactive like the alkali metals $$(N a, K)$$ and alkaline earth metals (Ca, Mg) and aluminum, then the reduction of the oxide can be done only by the electrolytic method.

The oxides of the less reactive metals such as zinc, iron, copper, lead, tin, manganese, chromium can be reduced by a number of reducing agents such as reduced by a carbon, carbon monoxide.

So carbon satisfactory reducing agent for all types of metal oxides.

Low melting metals like lead are refined by _________.

Low melting metals like lead are refined by liquation. Metals with low melting point containing impurities of high melting point can be purified by liquation because the liquation separation is based on differences in the melting point and density of alloy and on the low level of mutual solubility of the constituents.

Answer the following questions based on the extraction of aluminium from alumina by Hall Heroults Process:
(i) What is the function of cryolite used along with alumina as the electrolyte?
(ii) Why is powdered coke sprinkled on top of the electrolyte?
(iii) Name the electrode, from which aluminium is collected.

(i) Cryolite acts as a solvent and lower the fusion temperature from $$2050^oC$$ to $$950^oC$$.
(ii) A layer of powdered coke is sprinkled over the surface of the electrolyte to reduce the heat loss by radiation and prevent the carbon rod from binning in air.
(iii) Cathode

Ore	Impurity	Method
High density	Low density	(i)
Magnetic	Non magnetic	(ii)
Low density	High density	(iii)
Dissolved in the solvent	didn't dissolve	(iv)

General Principles And Processes Of Isolation Of Elements - Class 12 Engineering Chemistry - Extra Questions