# will the autoionization of water reduce due to common ion effect? [closed]

When a weak acid is added to water , will the dissociation of water reduce due to common ion effect caused by increased H+ concentration due to acid , my text book said common ion effect is caused by a strong electrolyte Moreover this doubt is a part of a larger doubt - if multiple weak acids are added in water will they reduce each others and water's dissociation as compared to their dissociation in their individual solutions ( due to common ion effect caused by H+ ions ) They should ? Having this doubt because the textbook I'm using just adds up their normal dissociations irrespective of common ion.

## closed as unclear what you're asking by andselisk♦, MaxW, Mithoron, Mathew Mahindaratne, Todd MinehardtJan 22 at 21:59

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• Yes, if you have multiple equilibria with common species, they will influence each other. If you put an acid in neutral water, the $\ce{H+}$ will increase of course, but at the same time, the $\ce{OH-}$ concentration will decrease. For the case with multiple weak acids, adding the first acid will change the pH, so the other acids will dissociate less just like when you add strong acid to a weak acid. – Karsten Theis Jan 20 at 21:19

Adding acid to the water will not stop the auto-ionization of the water, so: the auto-ionization will continue to give equal concentrations of hydroxide and hydronium. But the addition of acid to the water increases the concentration of the hydronium ions in the solution, pushing water balance with its ions to the left to resist the increase in the concentration of hydronium and reach a new equilibrium. The concentrations of hydronium and hydroxide produced by auto-ionization of water are reduced, where the concentrations of $$\ce{H_3 O^+}$$ or $$\ce{OH^-}$$ from water ionization is less than$$\pu{ 10^{-7}}$$.
$$\ce{{[H_3O^+]}_\text{(after acid addition)}=\ce{[H_3O^+]}_\text{(produced by acid dissociation)} +\ce{[OH^-]}_\text{(produced by water auto-ionization )}}$$
• You have two equilibria: water auto-ionization and acid dissociation, and you can use the following equation to calculate $\ce{[H_3O^+]}_\text{(after acid addition)}$:$$\ce{{[H^+]}=\frac{K_\mathrm{w}}{[H^+]}+\frac{K_\mathrm{a}\text{[Acid]}_\mathrm{I}}{\ce{[H^+]}+K_\mathrm{a}}}$$ – Adnan AL-Amleh Jan 21 at 21:26