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Question : 11
Total: 12
State the change in colour observed in each of the following cases mentioning the reason:
(a) Silver chloride is exposed to sunlight.
(b) A piece of zinc is dipped in ferrous sulphate solution.
(c) Copper powder is strongly heated in air.
(a) Silver chloride is exposed to sunlight.
(b) A piece of zinc is dipped in ferrous sulphate solution.
(c) Copper powder is strongly heated in air.
Solution:
(a) The decomposition of silver chloride to silver and chlorine in the presence of sunlight is known as Photolytic Decomposition. The white colour silver chloride decomposes to grey-white colour silver metal and yellowish colour chlorine gas.
The chemical reaction is given as:
2 AgCl ( s )
2 AgCl ( s ) + Cl 2 ( g )
(b) When zinc is added to solution of Iron (II) sulphate, the colour of iron sulphate solution changes. It is because zinc is more reactive than iron, therefore it displaces iron from its solution of iron sulphate and a grey precipitate of iron and a colourless solution of zinc sulphate is formed.
Zn + FeSO 4 → ZnSO 4 + Fe
(c) When copper powder is strongly heated in the presence of oxygen, it changes from brown to black because it reacts with oxygen to form copper oxide which is black in colour. Thus, the colour change is observed due to the formation of copper oxide.
2 Cu (brown) + O 2 → 2 CuO (black)
The chemical reaction is given as:
(b) When zinc is added to solution of Iron (II) sulphate, the colour of iron sulphate solution changes. It is because zinc is more reactive than iron, therefore it displaces iron from its solution of iron sulphate and a grey precipitate of iron and a colourless solution of zinc sulphate is formed.
(c) When copper powder is strongly heated in the presence of oxygen, it changes from brown to black because it reacts with oxygen to form copper oxide which is black in colour. Thus, the colour change is observed due to the formation of copper oxide.
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