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CBSE Questions for Class 8 Chemistry Materials Metals And Non Metals Quiz 7 - MCQExams.com
CBSE
Class 8 Chemistry
Materials Metals And Non Metals
Quiz 7
The reaction of aluminum atoms displacing hydrogen ions from sulphuric acid can be represented as:
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$$2Al+3H_2SO_4\rightarrow Al_2(SO_4)_3+3H_2$$
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$$Al+3H_2SO_4\rightarrow Al_2(SO_4)_3+H_2$$
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$$3Al+2H_2SO_4\rightarrow Al_3(SO_4)_2+2H_2$$
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$$2Al+6H_2SO_4\rightarrow Al_2(SO_4)_6+6H_2$$
Explanation
The reaction of aluminium atoms displacing hydrogen ions from sulphuric acid can be represented as:
$$2Al+3H_2SO_4\rightarrow Al_2(SO_4)_3+3H_2$$
This is the balanced chemical equation. The products formed are aluminium sulphate and hydrogen.
Which of the following is a good conductor of heat?
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Water
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Kerosene
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Iron
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Air
Explanation
Among the given options, iron is a metal. Metals generally are good conductors of heat. Water, kerosene and air are not metals. Also, they are not good conductors of heat.
State whether given statement is True or False :
When $$NaOH$$ reacts with zinc it releases water.
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True
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False
Explanation
When a metal like zinc reacts with a base like $$NaOH$$, hydrogen gas is released which burns with a pop sound.
$$2NaOH + Zn \rightarrow Na_2ZnO_2 + H_2$$
(Sodium zincates)
Among non-metals, .......... is a ........... conductor of electricity.
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chlorine, good
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graphite, good
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sulphur, good
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oxygen, good
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None of these
Explanation
Generally, non-metals are bad conductors of electricity. Chlorine, sulphur and oxygen are bad conductors.
However, graphite is one of the few exceptions among non-metals that are good conductors of electricity.
Metals are generally good conductors of heat.
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True
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False
Explanation
Metals are generally good at conducting heat. That is why they are used to make cooking utensils.
So, the given statement is true.
An element that conducts heat energy well and is easily shaped is a
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metal
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plastic
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non-metal
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None of the above
Explanation
Metals are generally good conductors of heat, and are malleable and ductile (can be easily shaped). Plastic is a non-metal. Non-metals are generally bad conductors of heat.
Metals react with water to form :
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oxides
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hydroxides
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Both of them
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None of these
Silver jewellery tarnish in the presence of moisture and:
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Sulphur compounds
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Nitrogen
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Oxygen
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Carbon dioxide
Explanation
Tarnish of Silver jewellery is result of chemical reaction of Silver with Sulphur containing substances in the air forming Silver sulphide which is black in colour.
Name the metal which offers higher resistance to the passage of electricity than copper.
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Gold
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Silver
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Mercury
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None of these
Which of the following is correct about metallic character?
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Si < Be < Mg < Na < P
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Be < Mg < Na < Si < P
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P < Si < Be < Mg < Na
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P < Be < Mg < Na < B
Which one of the following metal burns, if kept in air?
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Aluminium
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Sodium
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Magnesium
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None of these
Which of the following components of air does not contribute to the tarnishing of metals?
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$${ CO }_{2}$$
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$${ O }_{2}$$
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$${ N }_{2}$$
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$${ H }_{2}O$$ vapour
Based on the physical properties of metals, indicate whether the following statement is true or false:
The metal caesium melts at high temperatures.
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True
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False
Based on the physical properties of metals, indicate whether the following statements are true or false:
Potassium is a hard metal.
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True
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False
Based on the physical properties of metals, indicate whether the following statement is true or false :
Platinum is a metal with poor malleability.
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True
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False
Explanation
Platinum is a metal with poor malleability.
Which of the following is not a substitutional solid solution?
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Brass
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Bronze
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Steel
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Monel metal
Explanation
Steel is an interstitial solid in which iron atoms occupy lattice sites and carbon atoms occupy interstitial sites.
Hence, option C is correct.
Generally, non-metals are not lustrous. Which of the following non-metals is lustrous?
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Sulphur
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Oxygen
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Nitrogen
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Iodine
Explanation
Hint: There is an exception in the lustrous property of non-metals.
Step 1:
When light falls on the surface of some material, it shines. This property of the material is called lustrous.
Step 2:
Generally metals are lustrous due to the vibration of the free mobile electrons when light falls on the surface of the metals. Non-metals are generally non-lustrous because
of the absence of free mobile electrons.
Step 3:
There is an exception in the lustrous property of non-metals. Iodine and diamond are non-metals that are lustrous. Iodine is lustrous because of the larger size, the outermost electrons are loosely bound, so the electrons on the surface of iodine become excited by absorbing heat energy from light when light falls on them and when they release this energy and come to their normal state, they emit this light making iodine lustrous.
Final step:
So, the correct option is
(D) Iodine
.
An oxide of a metal used for making soft drinks is :
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Sulphur dioxide
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Carbon monoxide
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Nitrogen Dioxide
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Carbon dioxide
Explanation
An oxide of a metal used for making soft drinks is Sulphur dioxide.
Hence, the correct option is $$A$$.
The ability of metals to be drawn into thin wire is known as_____.
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ductility
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malleability
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sonorous
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conductivity
Explanation
Hint: Generally metals are ductile.
Step 1:
Generally, metals can be drawn into a thin wire as they are ductile.
Step 2:
$$\bullet$$ The ability of metals to be drawn into a thin wire is known as ductility.
$$\bullet$$ The ability of metals to be hammered into a thin sheet is known as malleability.
$$\bullet$$ Metal produces a ringing sound when struck with a hard object and this property is called sonorous.
$$\bullet$$ Generally metal conducts heat and electricity and this property is called conductivity.
Step 3:
Metals can be drawn into a thin wire without breaking as metals are ductile but non-metals are not ductile. This property of metal is called ductility.
Final step:
So, the correct option is
A ductility.
Based on the physical properties of metals, indicate whether the following statements are true or false:
Copper is a good conductor of heat.
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True
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False
Based on the physical properties of metals, indicate whether the following statements are true or false:
One of the reasons for the use of gold in making ornaments is its metallic lustre.
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True
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False
Explanation
Gold is metal and is lustrous in appearance. Its lustre property makes it attractive. Also, its inertness increases its life. That's why it is used for making ornaments.
Based on the physical properties of metals, indicate whether the following statements are true or false:
Sodium is a hard metal.
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True
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False
Explanation
Generally metals are hard. But Sodium is exception. It is so soft that it can be cut using a knife.
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