positive ions move toward the negative electrode and negative ions toward the positive electrode

positive ions move toward the positive electrode and negative ions toward the negative electrode

both ions move toward both the electrodes in equal amounts until they are balanced

MCQ Questions for Class 12 Engineering Chemistry Electrochemistry Quiz 7

In the rusting of iron, iron has been:

0%
oxidised
0%
reduced
0%
vaporised
0%
decomposed

Explanation

In corrosion, metal is oxidised by loss of electrons to oxygen to form metal oxide. In rusting of iron, at one spot of the iron object oxidation occurs and that spot behaves as an anode.

Anode:

$Fe(s) → Fe^{2+}(aq) + 2e^-$

Cathode:

$4e^- + 4H^+(aq) + O_2(aq) → 2H_2O(l)$

Identify the false statement among the following:

0%
Oxidation takes place at positive electrode in electrolytic cell whereas at negative electrode in voltaic cell
0%
Deposition of metals takes place in both electrolytic cell and galvanic cell
0%
Direction of flow of current is from cathode to anode in electrolytic cell
0%
Both $A$ and $B$

During electrolysis, cations move towards the positive terminal.

0%
True
0%
False

Given the standard potential of the following at

$25^{\circ}C$ .

$MnO_{2}\, \rightarrow\, Mn^{3+}$ ;

$E^{\ominus}\, =\, 0.95\, V$

$Mn^{3+}\, \rightarrow\, Mn^{2+}$ ;

$E^{\ominus}\, =\, 1.51\, V$
The standard potential of

$MnO_{2}\, \rightarrow\, Mn^{2+}$ is :

0%
1.23 V
0%
0.2 V
0%
0.02 V
0%
None of these

Explanation

$2e^{-}\, +\, MnO_{2}\, \rightarrow\, Mn^{2+}$ ;

$E^{\ominus}$ = ?

$\Delta G\, =\, -\, 2FE^{\ominus}$
i.

$e^{-}\, +\, MnO_{2}\, \rightarrow\, Mn^{3+}$ ;

$\Delta G_{1}^{\ominus}\, =\, -\, FE^{\ominus}\, =\, -\, 0.95\, F$
ii.

$e^{-}\, +\, Mn^{3+}\, \rightarrow\, Mn^{3+}$ ;

$\Delta G_{2}^{\ominus}\, =\, -\, FE^{\ominus}\, =\, -\, 1.51\, E^{\ominus}$
Equations (i) + (ii) give the desired equation.

$\therefore - 2FE^{\ominus}\, =\, (- 0.95\, -\, 1.51) F$

$E^{\ominus}\, =\, 1.23\, V$

The half cell involving the reaction

$Cr_2O_7^{2-} (aq) + 14 H^+ (aq) + 6e \rightarrow 2Cr^{3+} (aq) + 7H_2O$ can be represented as :

0%
$Pt, H^+ (aq), Cr_2O_7^{2-} (aq)$
0%
$Pt, H^+ ,Cr^{3+} (aq)$
0%
$Pt, H_2, Cr_2O_7^{2-} (aq), Cr^{3+} (aq)$
0%
$Pt, H^+, Cr_2O_7^{2-} (aq), Cr^{3+} (aq)$

Explanation

It is reduction half cell of

$Cr_2O_7^{-2}$ and is represented as:

$(Pt), H^+, Cr_2O_7^{2-} (aq), Cr^{3+} (aq)$

Rusting of iron is catalysed by :

0%
H $^+$ ions
0%
dissolved $CO_2$ in water
0%
O $_2$
0%
impurities present

In the atmosphere of industrial smog, copper corrodes to form:

0%
basic copper carbonate and sulphate
0%
copper oxide
0%
copper sulphide
0%
copper nitrate

Which of the following statements is incorrect?

0%
Tarnishing of silver is due to the formation of $Ag_2S$ and $Ag_2O$
0%
Green deposit on Cu terminal of battery are due to the formation of $CuCO_3$
0%
Brown deposits on Fe is due to formation of rust
0%
White deposits on Al pan is due to the formation of $Al_2O_3$

Explanation

Explanation:

1). The composition of the tarnish layers on silver in air : It is often found to consist mainly of the sulphide $Ag_2S$ with some chloride $AgCl$ and oxide $Ag_2O$

$Ag+air(O_2+H_2S)\rightarrow Ag_2O+Ag_2S$

Hence option A is correct.

2). Green deposit on Cu terminal of the battery is due to the formation of :

$Cu+H_2O+CO_2+O_2\rightarrow CuCO_3+Cu(OH)_2$

Hence option B is correct.

3). Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the presence of water or air moisture.

Hence option C is correct.

4). The pesky white mineral deposit usually forms on the surface of your pans after boiling hard water. The white spots appear as a result of calcium and salt deposits.

Hence option D is wrong

Option D is the correct answer which is incorrect among all.

The tarnishing of silver ornaments in the atmosphere is due to the formation of:

0%
$Ag_2O, Ag_2S$
0%
$AgNO_3, Ag_2S$
0%
$AgOH, Ag_2CO_3$
0%
$Ag$

Explanation

In the air, a silver object tarnishes owing to the reaction of silver with hydrogen sulfide and oxygen.

Reaction:

$Ag+ air (O_2 + H_2S) \rightarrow Ag_2O + Ag_2S$

State True or False.

Corrosion of motor cars is the major problem in the winter, when salt is spread on road to melt ice and snow.

0%
True
0%
False

Electrolysis is the passage of electricity through a liquid or a solution accompanied by a chemical change.

0%
True
0%
False

State True or False.

Corrosion of iron is a redox process.

0%
True
0%
False

In moist air, iron is oxidized to give:

0%
iron $[II]$ oxide
0%
iron $[III]$ oxide
0%
iron $[II]$ hydroxide
0%
iron $[II]$ sulphide

Explanation

When iron is subjected to moist air it is oxidised as per the following reactions:

$Fe \rightarrow Fe^{2+} + 2e^-;$ Oxidation takes place

In the presence of moisture the following reaction takes place:

$2Fe^{2+} + 2H_2O + \dfrac{1}{2}O_2 \rightarrow Fe_2O_3 +4H^+$

$Fe_2O_3$ iron is in

$+3$ oxidation state.

Hence option B is correct.

Corrosion can not be prevented by which of the following method?

0%
Galvanisation
0%
Create a barrier between the object being corroded and oxygen
0%
Painting
0%
Exposing it to sunlight

Explanation

Corrosion can be prevented by creating a barrier between the object and oxygen. Galvanisation is a process to prevent corrosion and so is painting. However, exposing to sunlight is not a method to prevent corrosion.

Thus, option

$D$ is correct.

Assertion: Cations migrate at cathode during electrolysis.
Reason: Reduction always occurs at cathode.

0%
Both Assertion and Reason are true and Reason is the correct explanation of Assertion
0%
Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
0%
Assertion is true but Reason is false
0%
Assertion is false but Reason is true
0%
Both Assertion and Reason are false

Explanation

During electrolysis,
at anode:

$Y^- \rightarrow Y + e^-$
at cathode:

$X^+ + e^- \rightarrow X$

If edible oil is allowed to stand for a long time in an iron or tin container, the oil becomes rancid.

0%
True
0%
False

Which metals does not corrode easily?

0%
Gold
0%
Iron
0%
Aluminium
0%
Zinc

Explanation

In the activity series, metals are on the top of the series react and corrode easily as these metals are highly reactive like iron corrodes easily in the presence of water and air forming its oxide layer while metals present at the bottom are least reactive and do not corrode easily like gold, silver and platinum are some of them.

Option

$(A)$ is correct.

The resistance of solution decreases with increase in temperature.

0%
True
0%
False

An electrochemical cell stops working after some time because:

0%
electrode potential of both the electrodes becomes zero
0%
electrode potential of both the electrodes become equal.
0%
one of the electrode is eaten away.
0%
the reaction starts proceeding in opposite direction

When iron is rusted, it is :

0%
reduced
0%
oxidised
0%
evaporated
0%
decomposed

Given standard $E^{\ominus}$ :

$Fe^{3+}\, +\, 3e^-\, \rightarrow\, Fe$ ; $E^{\ominus}\, =\, -\, 0.036\, V$

$Fe^{2+}\, +\, 2e^-\, \rightarrow\, Fe$ ; $E^{\ominus}\, =\, -\, 0.440\, V$

The $E^{\ominus}$ of $Fe^{3+}\, +\, e^-\, \rightarrow\, Fe^{2+}$ is:

0%
$0.476 V$
0%
$0.404 V$
0%
$0.604 V$
0%
$0.772 V$

Explanation

$Fe^{3+}\, +\, 3e^-\, \rightarrow\, Fe\, (E_{1})$ .... (i)

$Fe^{2+}\, +\, 2e^-\, \rightarrow\, Fe\, (E_2)$ .... (ii)

Net equation $Fe^{3+}\, +\, e^-\, \rightarrow\, Fe^{2+}\, (E_3)$ .... (iii)

[Obtained by equation (i) - (ii)]

$E_3\, =\, \displaystyle \frac{n_1E_1\, -\, n_2E_2}{n_3}\, =\, \displaystyle \frac{3(-\, 0.036)\, -\, 2\, (-\, 0.440)}{1}$

$=\, 0.772\, V$

Option D is correct.

Total charge required to convert three moles of

$Mn_3O_4$ to

$MnO_4^{-}$ in alkaline medium will be:

0%
$10 F$
0%
$20F$
0%
$30 F$
0%
$40 F$

Explanation

$(Mn^{3/+8})_3\, \rightarrow\, 3Mn^{6+}\, +\, 10e^-$

$\therefore$ 10 Faraday charge is required for conversion of 1 mol of

$Mn_3O_4\, to\, MnO_4^{2-}$
so 30 faraday charge is required for 3 mole.

The rusting of iron takes place as follows : $2H^{+} +2e + \dfrac{1}{2} O_{2} \rightarrow H_2O(l) ; E^{o}= + 1.23 V$

$Fe^{2+} + 2e\rightarrow Fe(s); E^{o} = - 0.44 V$

$\Delta G^{o}$ for the net process is:

0%
$-322$ $kJ\ mol^{-1}$
0%
$-161$ $kJ\ mol^{-1}$
0%
$-152$ $kJ\ mol^{-1}$
0%
$-76$ $kJ\ mol^{-1}$

Explanation

$E^{\ominus}_{cell}\, =\, 1.23\, -\, (-\, 0.44)\, =\, 1.67\, V$

$\Rightarrow\, \Delta G^{\ominus}_{cell}\, =\, nFE^{\ominus}_{cell}\, =\, -2\, \times\, 96500\, \times\, 1.67\, J\, mol^{-1}$

$=\, -\, 332.3\, kJ\, mol^{-1}$

When the electric current is passed through a cell having an electrolyte, the positive ions move towards cathode and negative ions towards the anode. If the cathode is pulled out of the solution :-

0%
the positive and negative ions will move towards anode
0%
the positive ions will start moving towards the anode while negative ions will stop moving
0%
the negative ions will continue to move towards anode while positive ions will stop moving
0%
the positive and negative ions will start moving randomly

The presence of electrolytes ................ the rate of corrosion.

0%
increases
0%
decreases
0%
sharply decreases
0%
does not effect

20 mL of KOH solution was titrated with 0.20 M

$H_2SO_4$ solution in a conductivity cell. The data obtained were plotted to give the graph shown below.
The concentration of the KOH solution was :

0%
$0.30\, mol\, L^{-1}$
0%
$0.15\, mol\, L^{-1}$
0%
$0.12\, mol\, L^{-1}$
0%
$0.075\, mol\, L^{-1}$

_____ refers to amount of electricity while _____ refers to rate at which it flows.

0%
Ampere, coloumb
0%
Coloumb, ampere
0%
Faraday, coloumb
0%
Coloumb, faraday

Explanation

Coulomb refers to amount of electricity while ampere refers to rate at which it flows. Coulomb is the quantity of lctricity passed through a conductor/ electrolyte when a current of 1A strength flows for 1 second. In other words, coulomb

$=$ amperes

$\times$ second.

How many faradays are required to reduce one mole of

$MnO^{\ominus}_4$ to

$Mn^{2+}$ ?

0%
$1$
0%
$2$
0%
$3$
0%
$5$

Explanation

$\displaystyle { MnO }_{ 4 }^{ - }+{ 8H }^{ + }+{ 5e }^{ - }\longrightarrow { Mn }^{ 2+ }+{ 5H }_{ 2 }O$

$1$ mole of

$MnO_4^-$ requires 5 mole of electrons = 5 faradays.

The more negative the standard potential, the .............. is its ability to displace hydrogen from acids.

0%
Greater
0%
Lesser
0%
Negetivity of the satndard potential has nothing to do with displacement of hydrogen
0%
Depends on the acid

The process of breaking down of a compound by passing electric current through it is called:

0%
hydrolysis
0%
photosynthesis
0%
electrolysis
0%
distillation

Corrosion of metals can be prevented when contact between metal and .......... is cut off.

0%
Nitrogen
0%
Hydrogen
0%
Oxygen
0%
Carbon

Corrosion of metals can be prevented when contact between metal and ________ is cut off.

0%
nitrogen
0%
hydrogen
0%
oxygen
0%
carbon

Explanation

Corrosion is basically oxidation of metal in presence of oxygen. So it can be prevented by cutting off

${ O }_{ 2 }$

In an electrochemical cell that function as a voltaic cell:

0%
electrons move from the cathode to the anode
0%
electrons move through a salt-bridge
0%
electrons can move either from the cathode to the anode or from the anode to the cathode
0%
reduction occurs at the cathode

The amount of ion discharged during electrolysis is not directly proportional to :

0%
resistance
0%
time
0%
current
0%
chemical equivalent of ion

Explanation

The amount of ion discharged during electrolysis is not directly proportional to resistance. It is proportional to current, time and electro-chemical equivalent of the ion.

$m=Z \times i \times t$

Here,

$m$ is the amount of ion discharged,

$Z$ is the electrochemical equivalent,

$i$ is the current and

$t$ is time.

Option A is correct.

$CH_3COOH$ is titrated with NaOH solution. Which of the following statement is true?

0%
Conductance increases upto equivalence point, after which it decreases.
0%
Conductance decreases upto equivalence point, after which it increases.
0%
Conductance first increases (but not rapidly) upto equivalence point and then increases rapidly after equivalence point.
0%
none

Explanation

Weak Acid along with a Strong Base, example for acetic acid with NaOH:
Initially the conductance is low because of the feeble ionization of acetic acid. At the addition of base, there is reducing within conductance not only because of the replacement of

$H^+$ through

$Na^+$ but also suppresses the dissociation of acetic acid due to general ion acetate.
But extremely soon, the conductance increases on adding NaOH as NaOH neutralizes the un-dissociated

$CH_3COOH$ to

$CH_3COONa$ that is the strong electrolyte. This rise in conductance continues raise up to the equivalence point. The graph near the equivalence point is curved because the hydrolysis of salt

$CH_3COONa$ . Beyond the equivalence point, conductance increases more rapidly along with the addition of NaOH because of the highly conducting OH- ions display in the below figure.

In electrolysis :

0%
positive ions move toward the positive electrode and negative ions toward the negative electrode
0%
positive ions move toward the negative electrode and negative ions toward the positive electrode
0%
both ions move toward both the electrodes in equal amounts until they are balanced
0%
none of the above

On electrolysis, water splits into:

0%
positively charged hydrogen ions and negatively charged hydroxide ions
0%
negatively charged hydrogen ions and positively charged oxygen ions
0%
hydrogen and oxygen atoms having positive and negative charges respectively
0%
hydrogen and oxygen atoms having negative and positive charges respectively

Name the gas released at the cathode when acidulated water is electrolysed.

0%
Hydrogen
0%
Nitrogen
0%
Oxygen
0%
None of the above

Explanation

Acidulated water is a mixture of cold water and small amount if vinegar ,lemon juice or lime juice. it's just used as a soak to prevent discoloration of some fruits and vegetables that darken quikly when their cut surfaces are exposed to air. During electrolysis of acidulated water, hydrogen gas

$(H_2)$ is liberated at cathode.

Rusting of iron involves:

0%
oxidation
0%
reduction
0%
decomposition
0%
displacement

A compound which liberates reddish brown gas around the anode during electrolysis in its molten state is -

0%
Sodium chloride
0%
Copper (II) oxide
0%
Copper (II) sulphate
0%
Lead (II) bromide

Explanation

We know that Bromine gas is reddish brown in colour and which can only liberates during electrolysis of Lead (II) bromide $(PbBr_2)$

During electrolysis of Lead (II) bromide , Positive lead ions (cations) move to the cathode and gain electrons to become lead metal and . negative bromide ions (anions) move to the anode and loose an electron to make chlorine atoms. Two bromine atoms then combine and the diatomic bromine gas $(Br_2)$ is released at the anode.

Therefore, D is correct option.

Electrons are getting added to an element Y. Which electrode will Y migrate to during electrolysis?

0%
Anode
0%
Cathode
0%
will not migrate
0%
will move randomly

Explanation

On adding electrons to

$Y$ , it will get negatively charged and hence will migrate to positive electrode that is

$anode$ .

Answer_(A)

Which of the following methods is suitable for preventing an iron vessel from rusting ?

0%
Applying grease
0%
Applying paint
0%
Applying a coat of zinc
0%
All of the above.

Explanation

The rusting of iron can be prevented by painting, greasing or galvanising which is a process of applying a coat of zinc.

Hence, the correct option is

$\text{D}$ .

Which of the following statements is true ?

0%
Electrolysis is one of the applications of chemical effects of current
0%
A metal wire shows chemical effect when a current is passed through it
0%
Like charges attract each other
0%
Charge flows only through negative charge carriers

Aluminium is more reactive than iron. But aluminium is less easily corroded than iron because:

0%
aluminium is a noble metal
0%
oxygen forms a protective oxide layer on aluminium surface
0%
iron unergoes reaction easily with water
0%
iron forms both mono and divalent ions

What is the electric current required to deposit 0.972 g of chromium in three hours?
(E.C.E. of chromium is 0.00018 g/c)

0%
0.50A
0%
1A
0%
Zero
0%
2.5A

Explanation

ECE of chromium=

$0.00018g/C$ =mass of chromium deposited per coulomb of charge.

Hence charge needed for depositing

$0.972g$ of chromium

$=q=\dfrac{0.972}{0.00018}=5400C$

Time

$=t=3hr=3\times 3600s=10800s$

Current

$=I=\dfrac{q}{t}=\dfrac{5400}{10800}$

$\implies I=0.5A$

Answer-(A)

How much electricity must pass through acidulated water to release

$22, 400\, cm^3$ of hydrogen at N.T.P.?

0%
96500 C
0%
193000 C
0%
22.4 C
0%
95.5 C

Explanation

We know that

$22,400cm^3$ of

$H_2$ means

$1$ mole of

$H_2$ .

Now, we know that

$2H^{+}+2e^-\rightarrow H_2$

Hence, for production of 1 mole of

$H_2$ , two moles of

$e^-$ are required.

And, one mole of

$e^-$ constitutes

$96500C$

Hence, charge or electricity required

$=96500\times 2=193000C$

Answer-(B)

Rusting of iron is a chemical reaction. The reaction can be termed as:

0%
combination reaction
0%
addition reaction
0%
both (A) and (B)
0%
decomposition

Explanation

Rusting of iron is a combination reaction. It occurs as follows-

$Fe + H_2O + O_2 \rightarrow Fe_2O_3 xH_2O$

Select the correct statements about the electrolysis_________.

0%
Electric current is used to drive a non spontaneous reaction
0%
$\displaystyle \Delta G$ is positive for chemical process during electrolysis
0%
Cations and anions move towards the anode in the anode and cathode respectively
0%
Over voltage is generally associated with anode in the electrolysis of $\displaystyle NaCl(aq)$

Explanation

As we know, electrolysis is non-spontaneous so

$\Delta G$ is positive for chemical process during electrolysis.

Also, Cations and anions move towards the cathode and anode respectively.

The potential of a cell depends on the magnitude of the current that is flowing through it. The difference between the equilibrium potential, at zero current, and the potential when current flows is called overvoltage. The magnitude of the overvoltage depends on the composition of the electrode and electrolyte, as well as on the current. Generally, overvoltages are small, so predictions of electrode reactions based on standard electrode potentials are usually correct. However, in the electrolysis of aqueous sodium chloride, the overvoltage for the oxidation of water, which is a neutral molecule, is large enough to make it more difficult to oxidize than chloride ions.

A solution of sodium chloride discharges

$6.1 \times 10^{16} Na^+$ ions and

$4.6 \times 10^{16} Cl^-$ ions in 10 seconds. Find the current passing through the solution.

0%
1.7 mA
0%
1.8 mA
0%
1.9 mA
0%
1.6 mA

A voltaic cell converts:

0%
electrical energy into chemical energy
0%
chemical energy into electrical energy
0%
light energy into electrical energy
0%
mechanical energy into electrical energy

CBSE Questions for Class 12 Engineering Chemistry Electrochemistry Quiz 7 - MCQExams.com

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Practice Class 12 Engineering Chemistry Quiz Questions and Answers

CBSE Questions for Class 12 Engineering Chemistry Electrochemistry Quiz 7 - MCQExams.com

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Practice Class 12 Engineering Chemistry Quiz Questions and Answers

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