Question #046fa

2 Answers
Oct 3, 2015

pH=7

Explanation:

HCl is a strong acid and it will completely dissociate in water. However water will also dissociate to give H^+ and OH^- ions (auto ionization).

Therefore, from HCl the concentration of H^+ is [H^+]_(HCl)=10^(-8)M and from H_2O the concentration of H^+ is [H^+]_(H_2O)=10^(-7)M.

The pH is calculated from both concentrations [H^+]_(Total)=[H^+]_(H_2O)+[H^+]_(HCl)=10^(-7)M+10^(-8)M~~10^(-7)M

Therefore the pH=-log[H^+]_(Total)=-log10^-7=7

In this case, the concentration of HCl is too small to change the pH of water. The solution stays neutral.

Dec 27, 2015

Question is wrong and does not make sense.

Explanation:

The previous contributor did use the correct method to answer the question and in theory his answer is correct, but the answer makes no sense due to HCl being an acid so must have a pH lower than 7.
Hence, there must be a mistake in the actual question that was asked and this can in fact be proven if one uses the equilibrium constant for water K_w=[H^+][OH^-]=10^(-14).

This would imply that [OH^-]=10^(-14)/(1xx10^(-8)

=1xx10^(-6)M

>[H^+]

This is impossible for an acid it cannot have this.