3rd Chapter Metals and nonmetals

Question-1 In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Solution:
Anode is impure, thick block of metal M.
Cathode is a thin strip/wire of pure metal M.
Electrolyte is a suitable salt solution of metal M.

Question-2 State two ways to prevent the rusting of iron.
Solution:
By coating the surface of iron by rust proof paints.
By applying oil or grease to the surface of iron objects so that supply of air consisting of moisture is cut off form the surface.

Question-3 What are amphoteric oxides? Give two examples of amphoteric oxides.
Solution:
Amphoteric oxides are the oxides, which react with both acids and bases to form salt and water. E.g. ZnO and Al2O3.

Question-4 Name two metals, which will displace hydrogen from dilute acids, and two metals which will not.
Solution:
Very reactive metals like Zn and Mg displace hydrogen from dilute acids. On the other hand less reactive metals like Cu, Ag, etc. do not displace hydrogen from dilute acids.

Question-5 What types of oxides are formed when non-metals combine with oxygen?
Solution:
When non-metals combine with oxygen it forms either neutral or acidic oxides. CO is a neutral oxide; N2O5or N2O3 is an acidic oxide.

Question-6 Give reason
i. Metals replace hydrogen from dilute acids, where as non-metals do not.
ii. Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Solution:
i. Metals are electropositive in nature. They readily lose electrons. These electrons reduce the protons liberated from the acid to liberate hydrogen gas, where as non-metals possess a tendency to gain electrons and hence they do not furnish electrons to protons liberated from acids. Hence H2 gas is not liberated.
ii. As it is easier to reduce metal oxides to metal, prior to reduction, metal sulphides and carbonates must be converted to oxides.

Question-7 Differentiate between metals and non-metals on the basis of their chemical properties.
Solution:

Question-8 Explain why the surface of some metals acquires a dull appearance when exposed to air for a long time.
Solution:
This is due to the surface oxidation of metals when exposed to moist air. For e.g. copper turns green on its surface due to the formation of basic copper carbonate Cu(OH) 2. CuCO3. Similarly silver becomes black due to the formation of black Ag2S and Aluminium forms a white coating of Al2O3 on its surface.

Question-9 State which of the following metals would give hydrogen when added to dilute hydrochloric acid. i. Iron, ii. Copper iii. Magnesium
Copper does not react with dilute hydrochloric acid at all. This shows that copper is even less reactive than iron.

Question-10 Name a non-metallic element, which conducts electricity.
Solution:
Carbon in the form of graphite conducts electricity, as there is a free electron in each carbon atom, which moves freely in between the hexagonal layers.

Question-11 Which metals do not corrode easily?
Solution:
Gold and platinum and other noble metals do not corrode in air.

Question-12 What are alloys?
Solution:
Alloys are homogeneous mixtures of two or more metals, or a metal and a non-metal.E.g. steel, brass, bronze, etc.

Question-13 Define the following terms.
(i) Minerals
(ii) Ores
(iii) Gangue
Solution:
(i) Minerals
All compounds or elements, which occur naturally in the earth’s crust, are called minerals. Example: Alums, K2SO4.Al2(SO4)3 . 24 H2O, Bauxite Al2O3.2H2O
(ii) Ores
Those minerals from which a metal can be profitably extracted are called ores. Bauxite (Al2O3.2H2O) is the ore of Al, copper pyrite CuFeS2. All minerals are not ores but all ores are minerals.
(iii) Gangue
When an ore is mined from the earth, it is always found to be contaminated with sand rocky materials. The impurity of sand and rock materials present in the ore is known as gangue.

Question-14 Name two metals that are found in nature in the free state.
Solution:
Gold and platinum are found in the free state in nature.

Question-15 What is chemical process used for obtaining a metal from its oxide?

Question-16 Name two metals, which can form hydrides with metals.
Solution:
Sodium and calcium form stable hydrides on reacting with hydrogen.

Question-17 Does every mineral have a definite and a fixed composition? Explain.
Solution:
Yes, every mineral has a definite and a fixed composition. Minerals are widely distributed in the earth’s crust in the form of oxides, carbonates, sulphides, sulphates, nitrates, etc. These minerals are formed as a result of chemical changes taking place during the formation of earth.

Question-18 Explain the meaning of malleable and ductile.
Solution:
Malleable is being able to be beaten/hammered into thin sheets.
Ductile is being able to be drawn into thin wires.

Question-19

Question-20 You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Solution:
The sour substances such as lemon (or tamarind juice) contain acids. These acids dissolve the coating of copper oxide or basic copper carbonate present on the surface of tarnished copper vessels and make them shining red-brown again.

Question-21 Give an example of a metal which-
i. is a liquid at room temperature.
ii. can be easily cut with a knife.
iii. is the best conductor of heat.
iv. is a poor conductor of heat.
Solution:
i. Mercury is in liquid state at room temperature.
ii. Sodium and potassium are soft metals which can be easily cut with a knife.
iii. Silver is the best conductor of electricity.
iv. Mercury is a poor conductor of heat.

Question-22 Why is sodium kept immersed in kerosene?
Solution:
Sodium metal is kept immersed in kerosene to prevent their reaction with oxygen, moisture and carbon dioxide of air.

Question-23 Why do ionic compounds have high melting points?
Solution:
These compounds are made up of positive and negative ions. There is a strong force of attraction between the oppositively charged ions, so a lot of heat energy is required to break this force of attraction and melt the ionic compounds. This is why ionic compounds have high melting points.

Question-24 A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Solution:
Aqua regia (By volume, this contains 3 parts of concentrated hydrochloric acid and 1 part of concentrated nitric acid) is the solution, which is used to sparkle the bangles like new, but their weight will be reduced drastically.

Question-25 Write equations for the reactions of
(i) iron with water
(ii) calcium and potassium with water
Solution:

Question-26 What would you observe when zinc is added to a sodium of iron(II) sulphate? Write the chemical reaction that takes place?
Solution:
Zinc is more reactive (more electro positive) than iron. Therefore it displaces iron from its salt solution. The colour of ferrous sulphate is pale green which becomes colourless.

Question-27
Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test-tube over the burning sulphur.
What will be the action of this gas on:
Dry litmus paper?
Moist litmus paper?
Write a balanced chemical equation for the reaction taking place.
Solution:
a) When sulphur is brunt in air then sulphur dioxide gas is formed.
(i) Sulphur dioxide gas has no action on dry litmus paper.
(ii) Sulphur dioxide gas turns moist blue litmus paper to red.
b) S(s) + O2(g) —> SO2(g)

Question 28
What is the colour of aqueous solution of CuSO4 and FeSO4 as observed in the laboratory?
(a) CuSO4 – blue; FeSO4 – light green
(b) CuSO4 – blue; FeSO4 – dark green
(c) CuSO4 – green; FeSO4 – blue
(d) CuSO4 – green; FeSO4 – colourless
Answer:
(a) Colour of CuSO4 solution is blue and FeSO4 solution is light green.

Question 29
A student took four test tubes I, II, III and IV containing aluminium sulphate, copper sulphate? ferrous sulphate and zinc sulphate solutions respectively. He placed an iron strip in each of them.

In which test tube, he found a brown deposit?
(a) I
(b) II
(c) III
(d) IV
Answer:
(b) In test tube II, because Fe is more reactive than copper but less reactive than Al arid Zn.

Question 30.
Aluminium sulphate and copper sulphate solutions were taken in two test tubes I and II respectively. A few pieces of iron filings were then added to both the solutions. The four students A, B, C and D recorded their observations in the form of a table as given below:

Student	Al2(SO4)3 solution (I)	CuSO4 solution (II)
A	Colourless solution -> Light green	Blue colour is retained
B	Colourless solution -> No change	Blue colour solution -> Green
C	Colourless solution -> Light blue	Blue colour solution -> Green
D	No change in colour	Blue colour of solution fades

Which student has recorded the correct observation?
(a) D
(b) C
(c) B
(d) A
Answer:
(c) Student B
Iron does not react with Al2(SO4)3 solution because iron is less reactive than aluminium. But Fe being more reactive than Cu displaces Cu from CuSO4 solution.

Question 31
Aqueous solutions of zinc sulphate and iron sulphate were taken in test tubes I and II by four students A, B, C and D. Metal pieces of iron and zinc were dropped in the two solutions and observations made after several hours were recorded in the form of table as given below:

Student Solution	Metal	Solution	Colour change Deposit/coating of solution	Deposit/coating obtained
A	Fe	ZnSO4	Turned green	Silvery grey deposit
	Zn	FeSO4	No change	No change
B	Fe	ZnSO4	No change	Black deposit
	Zn	FeSO4	Colour faded	Grey coating
C	Fe	ZnSO4	No change	No change
	Zn	FeSO4	Turned colourless	Black deposit
D	Fe	ZnSO4	No change	Grey deposit
	Zn	FeSO4	No change.	Black deposit

Which student has given the correct report?
(a) B
(b) D
(c) A
(d) C
Answer:
(d) Student C
(i) Fe is less reactive than zinc. So,

(ii) Zn is more reactive than Fe, so it displaces iron as follows:

Question 32
2 mL each of cone. HCl, cone. HNO3 and a mixture of cone. HCl and cone. HNO3 in the ratio of 3 : 1 were taken in test tubes labelled as A, B and C. A small piece of metal was put in each test tube. No change occurred in test tubes A’and Bbut the metal got dissolved in test tube C. The metal could be
(a) Al
(b) Au
(c) Cu
(d) Pt
Answer:
(b, d) A mixture of cone. HCl and cone. HNO3 in the ratio of 3 : 1 is known as aqua-regia. Gold (Au) and platinum (Pt) dissolve only in aqua-regia as these metals are very less reactive.

Question 33
When an aluminium strip is kept (a) Green solution of FeSO4 slowly turns brown
(b) Green solution of FeSO4 rapidly turns brown
(c) No change in colour of FeSO4
(d) Green solution of FeSO4 slowly turns colourless
Answer:
(a) The green solution of ferrous sulphate slowly turns brown. As aluminium is more reactive than iron, it displaces iron from ferrous sulphate solution.

Question 34
Aluminium is used for making cooking utensils. Which of the following properties of aluminium are responsible for the same?
(i) Good thermal conductivity
(ii) Good electrical conductivity
(iii) Ductility
(iv) Fligh melting point
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (i) and (iv)
Answer:
(d) Good thermal conductivity, malleability, light weight and high melting point are the properties/of aluminium due to which it-is used for making cooking utensils.

Question 35
If copper is kept open in air, it slowly loses its shining brown surface and gains a green coating. It is due to the formation of
(a) CuSO4
(b) CuCO3
(c) CU(NO3)2
(d) CuO
Answer:
(b) Copper reacts with CO2 present in air and forms a green coating on its surface due to the formation of basic copper carbonate [CuCO3.Cu(OH)2] as:

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