Question

An aqueous solution of HCl has a pH of 2.0 When water is added to increase the pH to 5.0 the hydrogen ion concentration:

• A. increases 1000 fold
• B. decreased 1000 fold
• C. decreased 100 fold
• D. none of these

Answer 1

Answer: (B)

decreased 1000 fold

For the given aqueos solution of $HCl$ has pH=2,

$⟹\left[H^{+}\right]={10}^{-2}M$

After adding water pH=5,

So, $\left[H^{+}\right]={10}^{-5}M$

Hence the hydrogen ion concentration decreases to 1000 fold.