Question

What happens to acid when put in water?

Answer 1

It is conceived to increase the concentration of the hydronium ion, `H_3O^+`, the characteristic cation of water.

Explanation:

The lower hydrogen halides, `H-X`, `(X!=F)`, are all room temperature gases. They are all quite soluble in water, and in aqueous solution they are conceived to protonate the water molecule:

`HX + H_2O rarr H_3O^+ + X^-`

The `"hydronium"` or `"acidium ion"` is a cluster of 3-4 water molecules with an extra `H^+` added. We use representations such as `H^+` or `H_3O^+` for simplicity.