Question

What is the color of the solution formed on dipping the piece of iron in dilute sulphuric acid:
 $ (i) $ Colourless
 $ (ii) $ Colourless solution turns red
 $ (iii) $ Black
 $ (iv) $ Red

Answer 1

Hint: When Zinc is added to the dilute solution of the sulphuric acid the reaction takes place which will displace the atom from its original position. Initially zinc granules are silvered in colour. But when the reaction takes place the colour of the dilute sulphuric acid changes due to the displacement of the atoms.

Complete answer:
Zinc is a metal which can donate two electrons to make ionic bonds with other atoms. When the zinc granules are added into the solution of dilute sulphuric acid then the displacement of hydrogen atoms takes place. Therefore the zinc atom will displace the hydrogen atom of the sulphuric acid. This is known as single displacement reaction. This reaction can be represented as: $ + 2 $
In addition to above there is an evolution of Hydrogen gas during the reaction. Since zinc has valency of $ + 2 $ , therefore it replaces both hydrogen atoms of sulphuric acid. Initially the colour of zinc granules is silvered but when we add it to the dilute sulphuric acid it forms zinc sulphate which is colourless in nature. Therefore we can say that the colour of the solution becomes colourless in addition to the dilute sulphuric acid. Hence the correct option is $ (i) $ .

Note:
The above reaction is an example of a single displacement reaction because only a single atom replaces another atom. The evolution of hydrogen gas can also be checked by bringing a burning candle near. The gas will blow up the burning candle. Since zinc can donate two electrons, therefore it replaces both hydrogen and sulphuric acid.