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NCERT Solutions for Class 10 Science Chapter 3 - Metals and Non-metals

ncert solutions for class 10 science Ch.3 metals and non-metals. This ncert solutions will help students in solving questions and learning concepts given in the textbook in detail. NCERT Solutions for Class 10 Science, provides answers to all the questions printed at the end of every chapter as well as the questions included within a chapter.
Chapter 3 metals and non-metals from  ncert science class 10  is one of the very important chapters Of chemistry.

[A] QUESTIONS GIVEN ON PAGE NUMBER 40 OF THE TEXTBOOK

1. Give an example of a metal which

(i) Is a liquid at room temperature?

Ans. (i) Mercury

(ii) Can be easily cut with a knife?

Ans. (ii) Sodium

(iii) Is the best conductor of heat?

Ans. (iii) Silver

(iv) Is a poor conductor of heat?

Ans. (iv) Lead.

Q.2. Explain the meanings of malleable and ductile.

Ans. Malleable:- A substance that can be beaten into sheets is said to be malleable. For example, iron,copper, etc.

Ductile:- A substance that can be drawn into wires is called ductile. For example, gold, silver, etc.

[B] QUESTIONS GIVEN ON PAGE NUMBER 46 OF THE TEXTBOOK

Q.1. Why is sodium kept immersed in kerosene oil ?

Ans. Sodium reacts so vigorously with oxygen that it catches fire when kept in the open. Hence, to protect accidental fires, it is kept immersed in kerosene oil. It cannot be immersed in water because there is a violent reaction.

Q.2. Write equations for the reactions of

(i) Iron with Steam

(ii) Calcium and Potassium with Water.

Ans. (i) 3Fe (s) + 4H2O (g) ——► Fe3O4 (s) + 4H2 (g)

(ii)Ca (s) + 2H2O (I) ——► Ca(OH)2 (aq) + H2 (g)

 2K (s) + 2H2O (l) ——►2KOH (aq) + H2 (g)

Q.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 given above to answer the following questions about metals A, B, C and D.

(i) Which is the most reactive metal ?

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

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

Ans. (i) Out of iron, copper, zinc and silver, zinc is at the top of activity series. Then comesiron. B gives displacement reaction with iron(II) sulphate, therefore, B is most reactive metal.

(ii) If B is added to a solution of copper(II) sulphate, displacement reaction will take place.Blue colour of copper sulphate will fade and red-brown particles of copper will settle down.

               B + CuSO4 ——►BSO4 + Cu

(iii) The decreasing order of reactivity is :

                B > A > C >D

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

Ans. Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal.

Metal + Dil. Hydrochloric acid ——► Metal chloride + Hydrogen 

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, displacement reaction will take place.The colour of ferrous sulphate is pale green, which turns colourless.

FeSO4(Light green) + Zn → ZnSO4 (Colourless)+ Fe(s)

  

[C] QUESTIONS GIVEN ON PAGE NUMBER 49 OF THE TEXTBOOK

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.

Q.2. Why do ionic compounds have high melting points ?

Ans. There are strong forces of attraction between oppositely charged ions in ionic compounds.Considerable amount of energy is required to break strong inter-ionic attraction. Therefore, they have high melting points.

[D] QUESTIONS GIVEN ON PAGE NUMBER 53 OF THE TEXTBOOK

Q.1. Define the following terms :

(i) Mineral (ii) Ore and (iii) Gangue.

Ans. (i) Mineral : The elements or compounds which occur naturally in the earth's crust are known as minerals.

(ii) Ore : Minerals from which metal can be extracted profitably are called ores.

(iii) Gangue : Impurities such as soil and sand which are present in the minerals are called

gangue.

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

Ans. Gold and platinum.

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

Ans. A metal is obtained from its oxide by the process of reduction.

[E] QUESTIONS GIVEN ON PAGE NUMBER 55 OF THE TEXTBOOK

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

In which cases will you find displacement reactions taking place ?

Ans. Based on the activity series of the metals ,the displacement reaction will take place as shown below :

Q.2. Which metals do not corrode easily?

Ans. Metals which are placed at the bottom of reactivity series like silver, gold, platinum do not corrode easily because are least reactive.

Q.3. What are alloys ?

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

It is obtained by first melting the primary metal and then dissolving the other elements in it in definite proportion. It is then cooled at room temperature.

Exercise questions Page number 56-57

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

Solution:  (d) AgNO3 solution and Copper metal. Copper displaces silver from silver nitrate.

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

a) Applying grease b)Applying paint
c )Applyin a coating of zinc d) All of the above

Ans. 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.3 (a) Calcium reacts with oxygen to give CaO which has high melting point. It dissolves in water to give lime water

Ca +½O2 ——► CaO

CaO + H2O ——► Ca(OH)2.

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 more reactive than tin.

(d) Zinc is less reactive than tin.

Ans.4  (a) Zinc is more reactive than tin.The food  might reacts with zinc and get spoilt.Therefore,food cans are coated with tin not zinc.

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.

Solution:

Ans. (a) Place the sample on an iron block. Strike

with hammer. If the sample takes the shape of a sheet,it is a metal. If it breaks into pieces, it is a non-metal.

Set up an arrangement by using a bulb, a battery,

wires and a switch (Fig. 3.11). Insert the samples ofmetals and non-metals in the clips one by one and turn the switch on. If the bulb glows, the sample is a metal. If not, then the sample is a non-metal.

(b) The above two methods can, in general, be

used to distinguish between metals and non-metals.But there are some exceptions. For example, graphite,which is a form of carbon, a non-metal, is a conductor of electricity.

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

Solution:

Ans. Those metallic oxides which shows both acidic as well as basic behaviour are called amphoteric oxides. Such metal oxides react with both acids and bases.

Examples:- Aluminium oxide(Al2O3) and Zinc oxide (ZnO)

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

Ans.  More reactive Metals such as Calcium and magnesium  displace hydrogen from dilute acids whereas least metals such as gold and silver do not displace hydrogen from dilute acids.

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

Ans. Impure metal M is made the anode,a thin strip of pure metal M as the cathode and a solution of salt of metal M as the electrolyte.

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) Sulphur is non-metal. Oxides of non-metals are acidic. In this case Sulphur dioxide is produced which is acidic.

i) There will be no action of the gas on dry litmus paper.

ii) Wet litmus paper will turn red.

b) The balanced chemical equation can be written as under :

   S(s) + O2(g) ——► SO2(g)

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

Solution:

Ans. Rusting of iron can be prevented by 

i) by applying grease or paint    ii) by Galvanising.

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

Solution:

Ans. Acidic oxides are formed when non-metals combine with oxygen.

12. Give reasons

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

Ans. a) These metals are least reactive. They do not react with oxygen and bases present in air and with moisture. Thus, their shine is maintained. That is why these metals are used to make jewellery

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

Ans. b) Reaction of sodium, potassium and lithium with oxygen is so violent that they catch fire. Also we cannot store them under water because there is a brisk reaction. Hence, they are stored under oil.

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

Ans. (c) This is because aluminium is a good conductor of electricity. Aluminium forms a layer of aluminium oxide at high temperature after which it resists corrosion and does  not react with food.

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

Ans. (d) It is easier to reduce oxide than the carbonates and sulphides to the metal.

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. Copper, on keeping in air, reacts with atmospheric carbon dioxide to form a green layer of copper carbonate. Copper carbonate reacts with citric acid present in lemon or tartaric acid present in tarmarind to form soluble copper citrate or copper tartrate. The vessels are thus cleaned using water.

Copper carbonate + Citric acid ——► Copper citrate + Carbon dioxide + Water

Copper carbonate + Tartaric acid ——► Copper tartarate + Carbon dioxide + Water

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

Solution:

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 retreat. Can you play the detective to find out the nature of the solution he had used?

Ans. Aqua regia which is a mixture of 3 parts of concentrated hydrochloric acid 1 part of concentrated nitric acid dissolves gold. The man put the gold bangles in this solution. The outer dirty layer of gold bangles dissolved in aqua regia bringing out the shining bangles. As the outer layer of bangles dissolved in aqua regia, the weight was reduced drastically.

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

Ans. Electrical conductivity of a metal is decreased when it is alloyed with another metal or non-metal. Thus, the electrical conductivity of steel(which is an alloy) is much less than that of pure copper. That is why copper is used to make hot water tanks and not steel.