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.