Question

Question #046fa

Answer 1

`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.

Answer 2

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.