Cls 10 Sci Chp 3 Solsn

 Class 10 Science 

 Chapter 3 Metals and Non-Metals 

 Solutions 

Intext Questions

Page number 40

1. 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?

Ans:

(i) Mercury

(ii) Sodium

(iii) Silver

(iv) Lead

2. Explain the meanings of malleable and ductile.

Ans:

> Metals which can be beaten to sheets are said to be malleable

> Metals which can be drawn into thin wires are said to be ductile

Page number 46

1. Why is sodium kept immersed in kerosene oil?

Ans:

to prevent its reaction with oxygen, moisture and carbon dioxide of aired to prevent accidental fires.

2. Write equations for the reactions of

(i) iron with steam

(ii) calcium and potassium with water

Ans:

3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

Ca(s) + 2H2O(I) → Ca(OH)2(aq) + H2(g)

2K(s) + 2H2O(I) → 2KOH(aq) + 2H2(g)

3. Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows

Use the Table above to answer the following questions about metals A, B, C and D.

Which is the most reactive metal?

What would you observe if B is added to a solution of Copper (II) sulphate?

Arrange the metals A, B, C and D in the order of decreasing reactivity.

Ans:

(i) B is most reactive metal.

(ii) B will displace copper from copper sulphate.

(iii) Arrangement of metals in the order of decreasing reactivity B>A>C>D.

4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.

Ans:

Hydrogen gas is liberated when dilute HCl is added to a reactive metal.

Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)

5. What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.

Ans:

Zinc is more reactive (more electro positive) than iron. Therefore Zinc displaces Iron from its salt solution. The colour of ferrous sulphate is pale green, which turns colourless.

FeSO4 + Zn → ZnSO4 + Fe(s)

Page number 49

1. (i) Write the electron-dot structures for sodium oxygen and magnesium.

(ii) Show the formation of Na2O and MgO by the transfer of electrons.

(iii)What are the ions present in these compounds?

Ans:

(ii) Formation of Na2O and MgO:

(iii) In Na2O, ions present are Na+ and O2-.

In MgO, ions present are Mg2+ and O2-.

2. Why do ionic compounds have high melting points?

Ans:

Ionic compounds have strong electrostatic forces of attraction between the ions. Therefore, it requires a lot of energy to overcome these forces. That is why ionic compounds have high melting points.

Page number 53

1. Define the following terms.

(i) Mineral

(ii) Ore

(iii) Gangue

Ans:

(i) Mineral: The naturally occurring compounds of elements are known as Mineral.

(ii) Ore: Minerals from which metals can be extracted profitably are known as ores.

(iii) Gangue: The impurities present in the ore such as sand, rocks etc are non as gangue.

2. Name two metals which are found in nature in the free state

Ans: Gold and platinum

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

Ans:

Reduction process is used for obtaining a metal from its oxide.

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

ZnO(s) + C(s) → Zn(s) + CO(g)

Page number 55

1. Metallic oxides of zinc, magnesium and copper were heated with the following metals

Ans:

A more reactive metal can displace a less reactive metal from its oxide. But out of zinc, magnesium, and copper metals, magnesium is the most reactive, zinc is less reactive whereas copper is the least reactive metal.

2. Which metals do not corrode easily?

Ans:

Gold and platinum

3. What are alloys?

Ans: 

An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.

Exercise questions

1. Which of the following pairs will give displacement reactions?

(a) NaCl solution and copper metal

(b) MgCl2 solution and aluminium metal

(c) FeSO4 solution and silver metal

(d) AgNO3 solution and copper metal

Ans: (d) AgNO3 solution and copper metal

2. Which of the following methods is suitable for preventing an iron frying pan from rusting?

(a) Applying grease

(b) Applying paint.

(c) Applying a coating of zinc

(d) All the above.

Ans: (c) Applying a coating of zinc

3. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be

(a) calcium

(b) carbon

(c) silicon

(d) iron

Ans:  (a) Calcium.

4. Food cans are coated with tin and not with zinc because

(a) zinc is costlier than tin

(b) zinc has a higher melting point than tin

(c) zinc is less reactive than tin

(d) zinc is more reactive than tin.

Ans: (d) Zinc is more reactive than tin.

5. You are given a hammer, a battery, a bulb, wires and a switch.

(a) How could you use them to distinguish between samples of metals and non-metals?

(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.

Ans:

a) 

> Metals can be beaten into thin sheets with a hammer without breaking.

> Non-metals break into pieces when hammered.

> Metals are malleable, while non-metals are non-melleable.

> When metals are connected into circuit and the bulb glows.

> When non-metals (like sulphur) are connected, the bulb does not light up at all.

> Metals are good conductors of electricity.

b)

The above tests are useful in distinguishing between metals and non-metals

6. What are amphoteric oxides? Give two examples of amphoteric oxides

Ans:

metal oxides that react wtih both acids and bases to form salt and water are called amphoteric oxides.

Ex: Aluminium oxide and zinc oxide are amphoteric in nature.

7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Ans:

> Iron and aluminium will displace hydrogen from dilute acids as they more reactive then hydrogen.

> Mercury and copper cannot displace hydrogen from dilute acids as they are less reactive than hydrogen.

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

Ans:

Cathode – Pure metal

Anode – Impure metal

Electrolyte – Metal salt solution

9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.

(a) What will be the action of gas on

(i) dry litmus paper?

(ii) moist litmus paper?

(b) Write a balanced chemical equation for the reaction taking place.

Ans:

a) When sulphur powder is burnt in the air sulphur-di-oxide is formed.

(i) Sulphur-di-oxide does not have any effect on dry litmus paper.

(ii) Sulphur-di-oxide turn the moist litmus paper from blue to red as contact of SO2 with water turns to sulfurous acid.

(b) S(s) + O2(g) → SO2(g)

SO2(g) + H2O →H2SO3

10. State two ways to prevent the rusting of iron.

Ans:

Ways to prevent rusting of iron are :

(a) By painting

(b) By galvanizing

11. What type of oxides are formed when non-metals combine with oxygen?

Ans:

Non-metals combine with oxygen to form acidic oxides or neutral oxides.

12. Give reasons

(a) Platinum, gold and silver are used to make jewellery.

(b) Sodium, potassium and lithium are stored under oil.

c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction

Ans:

a) because these are malleable and ductile. These are highly resistant to corrosion.

b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water.

c) Aluminium forms a non-reactive layer of aluminium oxide on its surface. This layer prevents aluminium to react with other substances.

13. 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.

Ans:

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 makes them shining red-brown again.

14. Differentiate between metal and non-metal on the basis of their chemical properties.

Ans:

Metal:

> Metals are electropositive.

> Oxides of metal are basic in nature.

> Metals form chlorides which are electrovalent or ionic compounds.

> They react with water to form oxides and hydroxides. Some metals react with cold water, some with hot water, and some with steam. 

Non-metal:

> Non-metals are electronegative.

> Oxides of non-metals are acidic in nature.

> Non-metals form chlorides which are covalent compounds.
> They do not react with water.

15. 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 repeat. Can you play the detective to find out the nature of the solution he has used ?

Ans:

The solution he had used was Aqua regia. Aqua regia is Latin word which means ‘Royal Water’. It is the mixture of concentrated Hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It is capable of dissolving metals like Gold and Platinum. Since the outer layer of the gold bangles is dissolved in aqua regia so their weight was reduced drastically.

16. Give reasons why copper is used to make hot water tanks and not steel (analloy of iron).

Ans:

> Copper is a better conductor of heat than steel.

> Copper does not corrode easily. But steel corrodes easily.

> Copper does not react with water at any temperature, whereas iron reacts with water on heating.

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