question_answer 131)

  pH of a solution of a strong acid is 5.0. What will be the pH of the solution obtained after dilution the given solution a100 times?

Answer:

  \[pH=5\] \[\therefore \]\[[{{H}^{+}}]={{10}^{-5}}M\] Let 1 L of this solution is diluted to 100 L. \[{{M}_{1}}{{V}_{1}}={{M}_{2}}{{V}_{2}}\] \[{{10}^{-5}}\times 1={{M}_{2}}\times 100\] \[{{M}_{2}}={{10}^{-7}}M\] \[{{H}^{+}}\]ion contribution of water will also be considered because solution of acid is very dilute. \[{{[{{H}^{+}}]}_{Total}}={{[{{H}^{+}}]}_{Acid}}+{{[{{H}^{+}}]}_{Water}}\] \[={{10}^{-7}}+{{10}^{-7}}\] \[=2\times {{10}^{-7}}M\] \[pH=-{{\log }_{10}}[{{H}^{+}}]\] \[=-{{\log }_{10}}[2\times {{10}^{-7}}]=6.6989\]