Question

How do the two differ - (1) adding water to acid and (2) adding acid to water?

Answer 1

If you add water to acid reaction is exothermic and large amount of heat is released and the solution may boil very violently, splashing concentrated acid out of the container. Hoever, adding acid to water, the solution formed is very dilute and only small amount of heat is released. So it is always safer to add acid to water and not vice versa.

Answer 2

Adding water to acid will result in a very exothermic reaction.

Explanation:

When adding water first, there isn't enough water initially for it to absorb all of the heat the reaction makes, so the solution releases a lot of heat. This can make the solution bubble out of the apparatus you are using and spill everywhere.

Answer 3

It can make a violent reaction.

Explanation:

Adding water to acid the heat generated by instantaneously dilution reaction can yield a violent splash capable to burn the operator. But, If acid is added to water it should be gradually added allowing the water to dissipate the generated heat.

Answer 4

Let's consider both situations one by one:

• Adding water to acid:
  If you add water to acid then at first concentrated solution of acid is formed and a vigorous exothermic reaction takes place. And a lot of heat is released causing the solution to boil violently and acid splashes out of the container.
• Adding acid to water:
  On the other hand, if we want to move safe, then we should add acid to water. Because adding acid to water form dilute solution and also the small amount of heat is released which is not enough to boil the solution and also will not cause it to splash.

That's why it's always safer to add acid to water and not water to acid.

`Note:`
This rule is specifically important when you are working with strong acids i.e `H_2SO_4`.

Hope it helps...