A weak acid, HA and a $\mathrm{K}_a$ of $1.00 \times 10^{-5}$. If $0.100 \mathrm{~mol}$ of this acid is dissolved in one litre of water, the percentage of acid dissociated at equilibrium is closer to:

Given $\mathrm{K}_a=1.00 \times 10^{-5}, \mathrm{C}=0.100$ mol for a weak electrolyte, degree of dissociation $\propto=\sqrt{\frac{\mathrm{K}_a}{\mathrm{C}}}=\sqrt{\frac{1 \times 10^{-5}}{0.100}}=10^{-2}=1 \%$ Related Theory In any acid-base reaction, the equilibrium will favour the reaction that moves the proton to the stronger base. This equilibrium constant is referred to as the ion-product constant for water, Kw. In pure water, some molecules act as bases and some as acids.