pH of a solution of a strong acid is 5.0. What will be the pH of the solution obtained after diluting the given solution 100 times?
As per the information given in the question, we know that the pH=5.0
pH = 5 means [H+]=10−5 M,
On diluting it 100 times, we get
This should give pH = 7 but it cannot be so because solution is acidic and pH should be less than 7
The reason is that [H+] from H2O cannot be neglected. Thus, total [H+]=10−7M (from HCl) + 10−7M (from H2O ) =2×10−7M
∴pH=−log(2×10−7)= 7−0.3010=6.699