Question

How is the concentration of hydronium ions affected when a solution of acid is diluted?

Answer 1

Hint: Try to recall that hydronium means more water (solvent) molecules are surrounded by the hydronium. If you add more water i.e. dilute, then more number of water molecules is surrounded by hydronium and also, concentration is inversely proportional to volume. Now by using this you can easily answer the given question.

Complete step by step solution:
It is known to you that when an acid is strong then it is fully reacted with water and the number of hydronium ions already maxed out. The concentration will go down proportionally on increase in volume.
But, when an acid is weak, then the weak acid will not fully react with water and as you add more water, the reaction will proceed a little bit more each time. Eventually, in the extreme case of an infinitely dilute solution, the acid will be 100% ionized.
So, now we can say that the concentration of hydronium ions decreases when an acid is diluted because on adding water, the hydronium ion of acid and hydroxyl ions of water react to form water molecules and the concentration of hydronium ion decreases.

Note: It should be remembered to you that when we add water to an acid then its concentration and strength will definitely decrease.
Also, you should remember that if the solution of 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.