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SCIENCE CLASS 10CHAPTER - CHEMICAL REACTION AND EQUATIONS

PAGE - 6

QUESTION 1.

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

ANSWER

A magnesium ribbon is cleaned before burning in air to remove the layer of magnesium oxide from its surface so that it may readily combine with the oxygen on heating.

QUESTION 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

ANSWER

(i) H2 + Cl2 -------------- 2HCl
(ii) 3BaCl2 + Al2(SO4)3 ---------- 3BaSO4 + 2AlCl3
(iii) 2Na + 2H2O --------------- 2NaOH + H2

QUESTION 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.

ANSWER

(i) BaCl2 + Na2SO4 --------------- BaSO4 + 2NaCl
(ii) NaOH + HCl --------------- NaCl + H2O

PAGE - 10

QUESTION 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.

ANSWER

(i) The substance X used in white washing is Calcium oxide. Its Chemical formula is CaO.
(ii)     CaO  +  H2O  --------------------  Ca(OH)2

QUESTION 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.

ANSWER

The amount of gas collected in one of the process of electrolysis is double because water contains two part of hydrogen and one part of oxygen.

PAGE  -  13

QUESTION 1.

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

ANSWER

The blue colour of copper sulphate solution changes when an iron nail is dipped in it because iron displaces the copper from copper sulphate to form a light green solution of iron sulphate.

QUESTION 2.

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

ANSWER

Silver nitrate reacts with sodium chloride to form silver chloride and sodium nitrate.

          AgNO3 + NaCl --------------- AgCl + NaNO3

QUESTION 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)

ANSWER

(i) Substance oxidised : Na       
     Substance oxidised : O2

(ii) Substance oxidised : H2
      Substance oxidised : CuO

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