While preparing dilute sulphuric acid from concentrated sulphuric acid in the laboratory, the concentrated sulphuric acid is added slowly to water with constant stirring.

Explanation

In the process of dilution of concentrated sulphuric acid with water, very large amount of heat is liberated. This process is highly exothermic.
ii . As a result, if water is added to concentrated sulphuric acid, then water gets evaporated instantaneously. The mixture may splash out causing an accident.
In order to prevent this, the required amount of water is taken in a glass container and small quantity of concentrated sulphuric acid at a time is added with constant stirring. So, only a small amount of heat is liberated at a time. Hence, while preparing dilute sulphuric acid from concentrated sulphuric acid in the laboratory, the concentrated sulphuric acid 1s added slowly to water with constant stirring