Question

The concentration of hydronium ions $\left( {{H_3}{O^ + }} \right)$ decreases when a solution of acid is diluted.

Answer 1

We know that when acid is added into water then it dissociates into its ions one of them is always ${H^ + }$ ion. This ${H^ + }$ form hydronium ion. The concentration of hydronium ions is directly proportional to the number of hydronium ions per unit of volume. A solution is diluted by adding some water into it. Due to which volume changes.

Complete step by step answer:
-We know strong acids are completely dissociated into ions when added into water. One of the ions is ${H^ + }$ which is mainly found in acidic compounds. These ${H^ + }$ combine with water and form a hydronium ion. Hydronium ion represents an ${H^ + }$ ion in an aqueous medium. And the number of hydronium ions in the solution are maximum possible. When we dilute this solution or add some water into it then the number of hydronium ions remains the same but the volume increases due to decreases in the concentration of hydronium.
-But when a weak acid is added into water it partially dissociates into ions and there are some acid particles remaining in their original state. When you add more water into it, some of the remaining particles of acid dissociate into ions but if we observe the numbers of particles dissociates are less in comparison to the amount of water added. Then the concentration of hydronium ions also decreases in the case of a weak acid.
-In short, we can say that the concentration of hydronium ions always decreases when a solution of acid is diluted.
Hence the correct answer is option A.

Note:
It should be remembered to you that when we add water to acid then its concentration and strength will decrease.
Also, you should remember that if the solution of a weak acid or weak base which ionizes to a small extent salt is added having common ion then ionization of weak acid or weak base is further suppressed and this effect is known as common ion effect.