Question

Write the chemical reaction of when iron reacts with dil $ {H_2}S{O_4} $
(A) $ Fe + {H_2}S{O_4} \to FeS{O_4} + {H_2} \uparrow $
(B) $ 2Fe + 3{H_2}S{O_4} \to F{e_2}{(S{O_4})_3} + 3{H_2} \uparrow $
(C) $ 2Fe + 3{H_2}S{O_4} \to F{e_2}{(S{O_4})_3} + {H_2} \uparrow $
(D) $ 2Fe + {H_2}S{O_4} \to F{e_2}{(S{O_4})_3} + 3{H_2} \uparrow $

Answer 1

Hint: On the reaction of metals with acid formation of salt and evolution of hydrogen gas takes place. The hydrogen gas released can be detected by pop sound when the gas comes in contact with fire using a matchstick.

Complete solution
As we know that metals reacting with sulphuric acid release hydrogen gas and form salts. The hydrogen gas released gives a pop sound when came in contact with fire. For example-
$ Metal + Acid \to Salt + Hydrogen Gas \uparrow \\
  Mg + 2HCl \to MgC{l_2} + {H_2} \uparrow \\$
When iron is reacted with dil $ {H_2}S{O_4} $ , the iron readily forms iron (II) ions, i.e. $ F{e^{2 + }} $ ions.
On the reaction of iron with dilute sulphuric acid, thus formation of iron (II) sulphate takes place and the hydrogen gas is evolved. The reaction can be represented as –
 $ Fe(s) + {H_2}S{O_4}(dil) \to FeS{O_4}(s) + {H_2}(g) \uparrow $
The solution obtained after this reaction will be blue-green in appearance as the iron (II) sulphate formed has blue-green colour. This is because iron is a transition metal and the transition metals show colour in their compounds by $ d - d $ transition. In $ d - d $ transition the excitation of electrons from $ {t_{2g}} $ to $ {e_g} $ orbital takes place and there the electrons emit energy which gives colour in the visible range.
To convert $ F{e^{2 + }} $ into $ F{e^{3 + }} $ oxidation of iron (II) is required which can be done by good oxidising agents.
In dilute solution sulphuric acid behaves only as an acid, thus no oxidation occurred here. But in hot concentrated solutions, sulphuric acid reacts with iron, by oxidising $ F{e^{2 + }} $ into $ F{e^{3 + }} $ and then the compound ferric sulphate will be formed. The reaction will be represented as-
 $ 2Fe + 3{H_2}S{O_4} \to F{e_2}{(S{O_4})_3} + 3{H_2} \uparrow $
Hence the correct option is (A).

Note:
Hydrogen gas evolved in these reactions are used in the manufacturing of ammonia by Haber’s process. Also it is used in the oil refining process to remove sulphur from fuels. It is also used for the hydrogenation of unsaturated fats and oils.