Acid should be added to water but not water to the acid. Why ?

Explanation

1) The dissolving an acid or base in water is an highly exothennic process. Care must be taken while mixing concentrated `HNO_3` or concentrated `H_2SO_4` with water.
2) The acid must always be added slowly to water with constant stirring.
3) If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns.
4) The glass container may also break due to excessive local heating.