Q. 10.28 - An Introduction to General, Organic, and Biological Chemistry

Question

If a base is added to pure water, why does the $H_3{O}^{+}$ decrease?

Step-by-Step Solution

Answer

If a base is added to pure water, ${\mathrm{OH}}^{-}$ ion concentration increases, therefore the equilibrium shifts in backward direction and hence the $\left[{\mathrm{H}}_3{\mathrm{O}}^{+}\right]$ion concentration decreases.

Step 1: Given information

The aqueous cation ${\mathrm{H}}_3{\mathrm{O}}^{+}$, the method of hydronium ion .The ion formed by the addition of proton to water, is known as hydronium ion. When an Arrhenius acid dissolves in water, it releases a proton to the water molecules around it, resulting in a positive ion.

Step 2: Explanation

According to Le Chatelier's principle (or common ion effect), when a base is added to pure water, the concentration of ${\mathrm{OH}}^{-}$ ions increases, causing the equilibrium to shift backwards and the $\left[{\mathrm{H}}_3{\mathrm{O}}^{+}\right]$ to appear. The ion concentration drops.

$2H_{2}O\rightleftharpoons H_3{O}^{+}+O{H}^{-}$