NCERT Class 10 : Science-Intext Solutions

Chapter 01-Chemical Reactions and Equations-Intext Solutions

NCERT Book Page Number: 06

Q.1. Why should a magnesium ribbon be cleaned before burning in air?

Ans. Magnesium forms magnesium oxide when reacts with oxygen present in air. On the magnesium ribbon a stable layer of magnesium oxide is formed when it is stored, which prevents the further reaction of magnesium ribbon. Hence, to remove the layer of magnesium oxide, magnesium ribbon is cleaned before burning.

Q.2. Write the balanced equation for the following chemical reactions :
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
Ans. (i) $H_{2} + Cl_{2} \rightarrow 2HCl$
(ii) $3BaCl_{2} + Al_{2}(SO_{4})_{3} \rightarrow 3BaSO_{4} + 2AlCl_{3}$
(iii) $2Na + 2H_{2}O \rightarrow 2NaOH + H_{2}$

Q.3. Write a balanced chemical equation with state symbols for the following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Ans. (i) $BaCl_{2}(aq) + Na_{2}SO_{4}(aq)\rightarrow BaSO_{4}(s)$$ +  2NaCl(aq)$
(ii) $NaOH(aq) + HCl(aq) \rightarrow NaCl(aq) +$$ H_{2}O(l)$

NCERT Book Page Number: 10

Q.1. A solution of a substance ‘X’ is used for white washing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.
Ans. (i) The chemical name of substance, ‘X’ which is used for white washing is Calcium oxide. Its common name is lime or quick lime.
The chemical formula of calcium oxide is CaO.
(ii) $ CaO  + H_{2}O\rightarrow Ca(OH)_{2} $
When calcium oxide reacts with water it forms calcium hydroxide. Calcium hydroxide is also known as slaked lime.
Q.2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.
Ans.When electric current is passed through water it decomposes into its constituent components, i.e. hydrogen and oxygen gases. During electrolysis of water hydrogen gas collected in one test tube and is twice in volume than oxygen collected in another test tube. This is because a water molecule is formed by the combination of hydrogen and oxygen in the ratio of 2:1.

NCERT Science Book Page Number: 13

Q.1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Ans. The colour of copper sulphate solution is blue. When an iron nail is dipped in the solution of copper sulphate, it forms ferrous sulphate solution and copper metal by the displacement of copper from the solution.
The colour of ferrous sulphate is green. That’s why the solution becomes green.

Q.2. Give an example of a double displacement reaction other than the one given in Activity 1.10.
Ans. $ Pb(NO_{3}(aq) + 2Kl(aq)\rightarrow 2KNO_{3}(aq) $$+ Pbl_{2}(s)$

When lead nitrate reacts with potassium iodide, potassium nitrate and lead iodide are formed. In this reaction both the reactants exchange their ions after reaction. This type of reaction is known as double displacement reaction.
Q.3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) $4Na(s) + O_{2}(g)\rightarrow 2Na_{2}O(s)$
(ii) $CuO(s) + H_{2}(g)\rightarrow Cu(s) + H_{2}O(l)$
Ans. (i) In this reaction sodium is combined with oxygen, i.e. gains oxygen and hence oxidized. Consequently oxygen is reduced.
(ii) In this reaction hydrogen gains oxygen and forms water, hence it is oxidised. On the other hand copper loses oxygen and hence, reduced.