Chapter 16, Problem 1ALQ

You are asked for the H+ concentration in a solution of NaOH(aq). Because sodium hydroxide is a strong base, can we say there is no H⁺. since having H+ would imply that the solution is acidic?

Interpretation Introduction

Interpretation:

Whether there are any H+ present in a solution of NaOH_{( a q )} should be explained.

Concept Introduction:

Water is an amphoteric substance which means it can behave as either as an acid or as a base. We can see this clearly in the ionization of water. A proton from one water molecule is transferred to another water molecule to produce a hydroxide ion and a hydronium ion.

${\text{H}}_{\text{2}}{\text{O}}_{\text{(l)}}{\text{ + H}}_{\text{2}}{\text{O}}_{\text{(l)}}⥄{\text{H}}_{\text{3}}{\text{O}}_{\text{(aq)}}^{\text{+}}{\text{ + OH}}_{\text{(aq)}}^{\text{-}}$

In this water molecule that removing a proton acts as the acid and water molecule that accepts the proton acts as the base. The forward reaction does not occur in great extent. In pure water only few amount of hydronium ion and hydroxide ions present and they are equal. At ${25}^0\text{C}$ the actual concentrations are ${\text{[H}}_{\text{3}}{\text{O}}^{\text{+}}{\text{] = [OH}}^{\text{-}}\text{] = 1}{\text{.0×10}}^{\text{-7}}\text{ M}$. The product of hydronium ion and hydroxyl ion is always constant. We call this constant, the ion product constant, K_w. Thus, at ${25}^0\text{C}$, ${\text{[H}}_{\text{3}}{\text{O}}^{\text{+}}{\text{][OH}}^{\text{-}}\text{] = 1}{\text{.0×10}}^{\text{-14}}={\text{K}}_{\text{w}}$.

Answer to Problem 1ALQ

There are H+ present in an aqueous solution of NaOH.

Explanation of Solution

Since this is an aqueous solution of NaOH, H₂ O molecules are also present. According to the meaning of ion-product constant, at constant temperature, in any aqueous solution the product of [H⁺ ] and [OH^- ] must be constant. If we add a base to water, we get a basic solution. In this case because we have added a source of OH- the [OH^- ] will be greater than the [H⁺ ]. So the equilibrium ${\text{H}}_{\text{2}}{\text{O}}_{\text{(l)}}{\text{ + H}}_{\text{2}}{\text{O}}_{\text{(l)}}⥄{\text{H}}_{\text{3}}{\text{O}}_{\text{(aq)}}^{\text{+}}{\text{ + OH}}_{\text{(aq)}}^{\text{-}}$ will tend more towards left hand side making more water molecules. But still tiny amount of H+ is present because the ion product should be constant.

Conclusion

There are H+ present in an aqueous solution of NaOH.