Sunday, June 19, 2022

Class 10 Science | Intext Questions & Answers | Chapter 1 | Chemical Reactions and Equations


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


It is cleaned to remove Magnesium oxide coating and impurities from the ribbon. Then only it can burn in air.

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


(i)       H2 + Cl2 2HCl

(ii)      3BaCl2 + Al2(SO4)3 3BaSO4 + 2AlCl3

(iii)     2Na + 2H2O 2NaOH + H2

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.


(i)     BaCl2 (aq) + Na2SO4 (aq) BaSO4 (s) + 2NaCl (aq)

(ii)    NaOH (aq) + HCl (aq) NaCl (aq) + H2O (l)


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.


(i)     X= Calcium oxide (Quick Lime). Chemical formula = CaO.

(ii)    Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime).

CaO (s) + H2O (l) Ca(OH)2 (aq)

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.


The gas is hydrogen. At cathode, double amount of hydrogen gas is collected in test tube because during the break down of water, 2H molecule is released with 1 oxygen molecule.


1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?


When an iron nail is dipped in CuSO4 solution, iron displaces copper from the CuSO4 because iron is more reactive than copper. So the colour of the CuSO4 solution changes.

Fe (s) + CuSO4 (aq) FeSO4 (aq) + Cu (s)

2. Give an example of a double displacement reaction other than the one given in Activity 1.10.


2KBr (aq) + BaI2 (aq) 2KI (aq) + BaBr2 (aq)

3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.

(i)     4Na (s) + O2 (g) 2Na2O (s)

(ii)    CuO (s) + H2 (g) Cu (s) + H2O (l)


(i)     Sodium (Na) is oxidised and oxygen is reduced.

(ii)    Copper oxide (CuO) is reduced and H2 is oxidised.

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