Question

The concentration of hydronium ions \[({H_3}{O^ + })\] decreases when a solution of an acid is diluted.
A. True
B. False

Answer 1

Hint: Hydronium ion is a positive ion. This ion is formed when a water molecule accepts a hydrogen ion by the lone pair of oxygen. It is formed in an acidic solution of water. The formula of hydronium ion is, \[{H_3}{O^ + }\] .

Complete step by step answer:
When a solution of an acid has diluted the concentration of hydronium ions decreases, as the volume of the solution increases the concentration of hydronium ions remains the same so acidity decreases.
So, the given statement is true.

Therefore, the correct option is A.

Additional information:
Ostwald’s dilution law is used to describe the dissociation constant of the weak electrolyte with the degree of dissociation \[(\alpha )\] and the concentration of the weak electrolyte(C).
Let us take a binary electrolyte AB which dissociates into \[{A^ + }\] and \[{B^ - }\] ions.
Such that, \[AB \rightleftharpoons {A^ + } + {B^ - }\]
For very weak electrolytes, we know that degree of dissociation is very less i.e. \[\alpha < < < 1\] ,
Therefore, dissociation constant K will be \[K = C{\alpha ^2}\] ,
From this, we get the degree of dissociation of any ion \[\alpha = \sqrt {\tfrac{K}{C}} \]
Where, K =dissociation constant of a weak acid
 \[\alpha = \] degree of dissociation and c is the concentration of ions present.
Many factors affect the degree of dissociation. These are the nature of the electrolyte, nature of the solvent, nature of other substances present in solvent, dilution, and temperature.
When more amount of solvent such as water is added to the solution, it results in dissociating the molecules into ions of a weak electrolyte. Thus, the degree of dissociation of the weak electrolyte increases upon dilution.

Note: The Ostwald’s dilution law holds good only for weak electrolytes and fails in the case of strong electrolytes because strong electrolytes completely ionize at all dilution.