Question

The concentration of hydroxide ions ($$O{H}^{-}$$) is affected when excess base is dissolved in a solution of sodium hydroxide. The concentration of base in the new solution will:
(A) Increase
(B) Decrease
(C) Remain same
(D) None of these

Answer 1

Hint: To answer this question, we should know that, as the concentration of hydrogen ions in a solution increases, the more acidic the solution becomes and similarly as the level of hydroxide ions increases the more basic, or alkaline, the solution becomes.

Complete step by step solution:
To answer this question, we should first know about acid and bases. Do you ever think, how you can describe an acid or base?
So, in chemistry we will learn about three major classifications of substances known as acids or bases. We should know about Arrhenius' way of classification. His definition states that an acid produces $$H^{+}$$in solution and a base produces$$O{H}^{-}$$. This theory was developed by Svante Arrhenius in 1883. Later, two more sophisticated and general theories were proposed. These are the Brønsted-Lowry and the Lewis definitions of acids and bases.
So, according to Arrhenius classification it states that when we dissolve acid in an aqueous solution, certain ions were released into the solution. An Arrhenius acid is a compound that increases the concentration of H+ ions. These H+ ions form the hydronium ion (H3O+) when they combine with water molecules.
And similarly, we can describe base. We should know that base is a compound that increases the concentration of OH- ions that are present when added to water. The dissociation is represented by the following equation:
$$\begin{array}{rl}& NaOH\left(aq\right)\to N{a}^{+}\left(aq\right)+O{H}^{-}\left(aq\right)\end{array}$$
In this reaction, sodium hydroxide (NaOH) dissociates into sodium ($$N{a}^{+}$$)and hydroxide ($$O{H}^{-}$$) ions when dissolved in water, thereby releasing $$O{H}^{-}$$ions into solution.
So, from the above discussion we came to know that as the concentration of hydroxide ions increases the basicity of that solution will increase. When we add excess base to the solution, the concentration of hydroxide ion will also increase. This happens only when base added dissolves in water. If the base is not soluble in water, the concentration of hydroxide ions remains constant. So, the answer to this question is option A.




Note: We should also know about Brønsted-Lowry Theory of Acids and Base. This theory defines acid and base as follows:
We should know that a Brønsted-Lowry acid is a proton (hydrogen ion) donor and Brønsted-Lowry base is a proton (hydrogen ion) acceptor. In this theory, an acid is a substance that can release a proton (like in the Arrhenius theory) and a base is a substance that can accept a proton.