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

Question : 4. 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:

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, Fe(s) + ZnSO₄ (aq) ——→ No reaction (ii) Zn is more reactive than Fe, so it displaces iron as follows: Zn(s) + FeSO₄ (aq) ——→ Fe(s) + ZnSO₄ (aq) Zinc green Black deposit Colourless

Question : 5. 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 [NCERT Exemplar]
(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 : 6. 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 : 7. 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) Flight melting point [NCERT Exemplar]
(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 : 8. 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 [NCERT Exemplar]
(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:

2Cu + O₂+ CO₂ + H₂O——→ CuCO₃.Cu(OH)

Additional Questions

Question : 1 a) Due to which property of metals are metallic foils prepared?
b) Write uses of aluminium foils

Answer :
a) Metallic foils are prepared, making use of the malleable property of metals.
b) Aluminium foils are used for

(i) wrapping chocolates and food stuff
(ii) to prepare hydrogen.

Question : 2 Name one non-metal and one metal, which are in liquid state at room temperature.

Answer :
Bromine is the non–metal and mercury is the metal which are in liquid state at room temperature.

Question : 3 Give reasons for the following
i) Zinc oxide is considered an amphoteric oxide.
ii) Non-metals in general do not displace hydrogen from dilute acids.
iii) Metals conduct electricity.

Answer :
i) Zinc oxide is considered an amphoteric oxide because it shows both acidic and basic behaviour.
ii) Non-metals do not react with dilute acids hence do not displace hydrogen from dilute acids.
iii) That metals conduct electricity because they contain free electrons which can move easily through the metal and conduct electric current.

Question : 4 Identify the following oxides with neutral, acidic, basic and amphoteric oxides.
i) Al₂O₃
ii) MgO
iii) SO₂
iv) CO;
v) Na₂O
vi) N₂O
vii) ZnO
viii) CO₂
ix) SO₃
x) CaO.

Answer :
Neutral oxides: CO; N₂O
Acidic oxides: SO₂; CO₂; SO₃
Basic oxides: MgO; Na2O; CaO
Amphoteric oxides: Al₂O₃ZnO

Question : 5 By what processes do you concentrate the following ores:
i) PbS(galena)
ii) Fe₂O₃(haematite)
iii) Al₂O₃.2H₂O (bauxite).

Answer :
i) PbS (galena) is concentrated by froth floatation method.
ii) Fe₂O₃ (haematite) is concentrated by magnetic separation.
iii) Al₂O₃.2H₂O (bauxite) is concentrated by leaching process (chemical method).

Question : 6 Why is that iron does not occur as a metal in the crust of the earth? What are the common compound forms in which iron occurs? Which of these is more often used for extracting iron? Why are carbon and limestone mixed with iron ore before feeding it into the blast furnace? Write the chemical equations for the reduction step and the slag formation step.

Answer :
Iron is quite reactive and so it does not occur as a metal in the crust of the earth. The common compounds formed are its oxide, a carbonate and a sulphide. The oxide ore of iron called haematite is more often used for extracting iron. The carbon and limestone which is mixed with iron ore is called the charge. This charge is responsible for the formation of iron metal. Coke acts the reducing agent and addition of limestone helps to remove the earthy impurities like sand from the blast furnace by forming fusible slag.
Reduction of Iron(III)oxide or haematite to Iron: carbon monoxide reduces iron(III)oxide to iron metal

Fe₂O₃ + 3CO (g) → 2Fe + 3CO₂ (g)

1: In the blast furnace limestone decomposes to form calcium oxide and carbon oxide.

CaCO₃ (S) → CaO(s) + CO₂ (g)

2: This calcium oxide reacts with sand and form molten calcium silicate called slag.

CaO (s) + SiO₂→ CaSiO₃(I)
             slag

Question : 7 By what chemical processes do you obtain the following metals?
i) Mercury from HgO
ii) Iron from Fe₂O₃
iii) Manganese from MnO₂
iv) Sodium form NaCl v) Aluminium from Al₂O₃.

Answer :
i) Mercury from Murcuric Oxide can be obtained by simple heating.
2HgO → 2Hg + O₂
ii) Iron from Iron Oxide (Fe₂O₃) can be obtained by carbon reduction method i.e. heating with coke.
2C + O₂→ 2CO
Fe₂O₃ + 3CO → 2Fe + 3CO₂
iii) Manganese from manganesedioxide is obtained by alumina thermite process, i.e. heating with aluminium
3MnO₂ + 4Al → 2Al₂O₃ + 3Mn
iv) Sodium from sodium chloride is obtained by electrolytic reduction (electrolysis) of fused NaCl.
NaCl← → Na⁺ + Cl^–
At anode 2Cl^–→ Cl₂ + 2e^–

At Cathode 2[Na^– + e^–→ Na]

v) 2Al₂O₃←→ 2Al³⁺ + 3(O)^2-

At cathode 4[2Al³⁺ + 6(e) → 2Al]

At cathode 6O^2-→ 3O₂ + 12 e^–

Question : 8 i) What is the composition of molten slag, formed in the extraction of iron in the blast furnace?
ii) What is the use of slag?

Answer :
i) Molten slag in the extraction of iron is calcium silicate(CaSiO₃).
ii) Slag is used for constructions of roads.

Question : 9 Write the name of the compound, when iron is corroded?

Answer :
When iron is corroded rust is formed which is hydrated iron (III) oxide (Fe₂O₃.x.H₂O)

Question : 10 Give reasons for the following
i. Na, K and Ca metals form hydrides by combination with hydrogen gas, but most other metals do not.
ii. Aluminium easily combines with oxygen but still it can be used for making kitchen utensils.

Answer :
i. Metals like Na, K and Ca can force the hydrogen atoms to accept electrons given by them and form hydrides.
ii. Aluminium forms a protective oxide layer when it combines with oxygen and hence it is used for making kitchen utensils.

Question : 11 i) Among iron and aluminium which rusts easily? ii) What are the conditions, necessary for rusting of iron?

Answer :
i) Among iron and aluminium, iron rusts easily. It forms Al₂O₃. That is why iron pipes are wrapped with aluminium metal to prevent rusting of iron.
ii) 1) Air or oxygen 2) Water, containing dissolved air. These are necessary conditions for rusting of iron.

Question : 12 Name an ore of zinc other than zinc oxide. By what process can this ore be converted to zinc oxide.

Answer :
Zinc blende(ZnS) is an ore of zinc other than zinc oxide. Roasting is the process by which ZnS can be converted into zinc oxide.

Question : 13 What property of hydrogen is observed in the following experiments?
i) Balloon, filled with hydrogen, floats.
ii) Pop sound is heard when a burning splint is introduced at the mouth of hydrogen filled jar.
iii) When black cupric oxide is heated in a stream of hydrogen, reddish colour is obtained.

Answer :
i) Hydrogen is light. So hydrogen filled balloons float.
ii) Pop sound is due to the combustible property of hydrogen. Hydrogen burns with oxygen at the mouth of the hydrogen filled jar.
iii) Hydrogen has reducing property. Hence it reduces black cupric oxide to red copper metal.

Question : 14 Select the non-metals amongst the following
i) Bismuth ii) Sulphur iii) Arsenic iv) Hydrogen.

Answer :
Hydrogen and Sulphur are the non-metals.

Question : 15 How do you test ammonia gas?

Answer :
Ammonia gas is tested, by showing a drop of conc. HCl by means of a glass rod to it, when dense white fumes of ammonium chloride are formed.
Ammonium chloride (dense white fumes).

Question : 16 Write chemical equations for reactions taking place when
i) Cinnabar is heated in air.
ii) Concentrated sulphuric acid and sulphur are heated together. Calcium metal reacts with water.

Answer :
I) Cinnabar is heated in air
2HgS + 3O₂ (g) → 2Hg)(s) + SO_s

II) Calcium metal reacts with water.
Ca(s) + 2H₂O (l) → Ca(OH)₂ (aq) + H₂(g)

Question : 17 What are the uses of ammonia?

Answer :
i) Ammonia is used in the manufacture of fertilizers like ammonium sulphate and ammonium nitrate.
ii) To manufacture nitric acid by Ostwald’s process.
iii) To prepare dyes, explosives, cellulose acetate etc.

Question : 18 Why do some metals like, Na, K, Ca, Mg not occur in nature as free elements?

Answer :
Metals like Na, K, etc (alkali metals) and Ca, Mg etc (alkaline earth metals) are very reactive and hence they react with atmospheric oxygen and carbon dioxide and also with other non-metals like sulphur present in the earth’s crust to form compounds like oxides, carbonates, sulphides, sulphates and chlorides. So they do not occur in free state, but are found in the form of the above compounds.

Question : 19 Write chemical equations for reactions taking place when:
i) Manganese dioxide is heated with aluminium powder.
ii) Steam is passed over hot iron.
iii) A mixture of ammonia and oxygen is passed over platinum heated to 1073 K.

Answer :
i) Manganese dioxide is heated with aluminium powder.
3MnO₂ + 4Al (s) → 3Mn(l) + Al₂O₃
ii) Steam is passed over hot iron.
3Fe(s) + 4H₂→ Fe₂O₃(s) + 4H₂
iii) A mixture of ammonia and oxygen is passed over platinum heated to 1073K.
4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O

Question : 20 Why are metals like sodium, calcium, magnesium, aluminium etc. obtained by electrolytic reduction?

Answer :
Metals like Na, Ca, Mg, Al etc. which are high up in the activity series are electropositive elements and possess a high affinity for oxygen. So their oxides are very much stable and cannot be reduced with common reducing agents like carbon. So carbon reduction process cannot be applied to prepare these metals. They can only be prepared by electrolytic reduction of their fused chlorides or oxides.

Question : 21 State briefly how you will extract iron from its ore. Draw a neat and labelled diagram. Write all the chemical reactions involved in it.

Answer :
Iron is usually extracted from its chief ore, Haematite.
The various steps involved in the production of iron metal from haematite are as follows:
1. Concentration of ore
The concentration of haematite or is done by the method of hydraulic washing. The ore is spilt into small pieces and then washed in a stream of water to remove sand, clay. In this way ,a fairly concentrated ore is obtained and usually there is no need of any further concentration.

2. Calcination
The washed iron ore is then strongly heated in the absence of air to expel water sticking to it.

3. Reduction
The washed and dried ore is mixed with weighed quantities of coke and limestone and put into a blast furnace from the top .A blast of hot air is blown into the furnace from near its bottom. This air is to supply for the burning of coke.
The two reactions which take place in the blast furnace leading to the formation of iron metal are: formation of carbon monoxide and reduction of haematite.