Intext Exercise 1
Question 1:
Why should a magnesium ribbon be cleaned before burning in air?
Solution 1:
Magnesium is very reactive metal. When stored it reacts with oxygen to form a layer
magnesium oxide on its surface. This layer of magnesium oxide is quite stable and prevents
further reaction of magnesium with oxygen. The magnesium ribbon is cleaned by sand paper
to remove this layer so that the underlying metal can be exposed into air.
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
Solution 2:
i H2( g ) Cl2( g ) 2HCl( g )
ii 3BaCl2( s) Al2 SO4 3( s) 3BaSO4( s) 2 AlCl3( s)
iii 2Na( s) 2H2O(l ) 2NaOH(aq) H2( g )
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.
Solution 3:
i BaCl2(aq) Na2 SO4(aq) BaSO4( s) 2NaCl(aq)
ii NaOH(aq) HCl( aq) NaCl( aq) H2O(l )
, Intext Exercise 2
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.
Solution 1:
(i) The substance ‘X’ is calcium oxide. Its chemical formula is CaO.
(ii) Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime).
CaO( s ) H2O(l ) Ca(OH)2( aq)
Calcium oxide (Quick lime) Water Calcium hydroxide (Slaked lime)
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.
Solution 2:
Water (H2O) contains two parts hydrogen and one part oxygen. Therefore, the amount of
hydrogen and oxygen produced during electrolysis of water is in a 2:1 ratio. During
electrolysis, since hydrogen goes to one test tube and oxygen goes to another, the amount of
gas collected in one of the test tubes is double of the amount collected in the other.
Intext Exercise 3
Question 1:
Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Solution 1:
When an iron nail is placed in a copper sulphate solution, iron displaces copper from copper
sulphate solution forming iron sulphate, which is green in colour.
Fe( s ) CuSO4( aq)
FeSO4( aq) Cu( s)
Iron Copper sulphate Iron sulphate (Green colur) Copper
(Blue colour)
Therefore, the blue colour of copper sulphate solution fades and green colour appears.
Question 2:
Give an example of a double displacement reaction other than the one given in Activity1.10.
Solution 2:
Sodium carbonate reacts with calcium chloride to form calcium carbonate and
sodiumchloride.
Na 2CO3( aq) CaCl2( aq)
CaCO3( s) 2NaCl( aq)
Sodium carbonate Calcium chloride Calcium carbonate Sodium chloride
Question 1:
Why should a magnesium ribbon be cleaned before burning in air?
Solution 1:
Magnesium is very reactive metal. When stored it reacts with oxygen to form a layer
magnesium oxide on its surface. This layer of magnesium oxide is quite stable and prevents
further reaction of magnesium with oxygen. The magnesium ribbon is cleaned by sand paper
to remove this layer so that the underlying metal can be exposed into air.
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
Solution 2:
i H2( g ) Cl2( g ) 2HCl( g )
ii 3BaCl2( s) Al2 SO4 3( s) 3BaSO4( s) 2 AlCl3( s)
iii 2Na( s) 2H2O(l ) 2NaOH(aq) H2( g )
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.
Solution 3:
i BaCl2(aq) Na2 SO4(aq) BaSO4( s) 2NaCl(aq)
ii NaOH(aq) HCl( aq) NaCl( aq) H2O(l )
, Intext Exercise 2
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.
Solution 1:
(i) The substance ‘X’ is calcium oxide. Its chemical formula is CaO.
(ii) Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime).
CaO( s ) H2O(l ) Ca(OH)2( aq)
Calcium oxide (Quick lime) Water Calcium hydroxide (Slaked lime)
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.
Solution 2:
Water (H2O) contains two parts hydrogen and one part oxygen. Therefore, the amount of
hydrogen and oxygen produced during electrolysis of water is in a 2:1 ratio. During
electrolysis, since hydrogen goes to one test tube and oxygen goes to another, the amount of
gas collected in one of the test tubes is double of the amount collected in the other.
Intext Exercise 3
Question 1:
Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Solution 1:
When an iron nail is placed in a copper sulphate solution, iron displaces copper from copper
sulphate solution forming iron sulphate, which is green in colour.
Fe( s ) CuSO4( aq)
FeSO4( aq) Cu( s)
Iron Copper sulphate Iron sulphate (Green colur) Copper
(Blue colour)
Therefore, the blue colour of copper sulphate solution fades and green colour appears.
Question 2:
Give an example of a double displacement reaction other than the one given in Activity1.10.
Solution 2:
Sodium carbonate reacts with calcium chloride to form calcium carbonate and
sodiumchloride.
Na 2CO3( aq) CaCl2( aq)
CaCO3( s) 2NaCl( aq)
Sodium carbonate Calcium chloride Calcium carbonate Sodium chloride
