Question

Assertion: The addition of acid to a solution buffered to pH 7 slightly lowest the pH.

Reason: pH of any neutral solution always lowers on the addition of acids.

• A. Both Assertion and Reason are true and Reason is the correct explanation of Assertion
• B. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
• C. Assertion is true but Reason is false
• D. Assertion is false but Reason is true
  
• E. Both Assertion and Reason are false

Answer 1

The correct option is A Both Assertion and Reason are true and Reason is the correct explanation of Assertion

Let the pH of Buffered solution is 7.
$pH=-log\left[H^{+}\right]$
hence , the $\left[H^{+}\right]={10}^{-7}$
If we add the acid , say for example $HCl$ then let the increase in $\left[H^{+}\right]$ concentration is by ${10}^{-10}$. then new pH will be :
$pH=-log[{10}^{-7}+{10}^{-10}]$
$pH=-(-6.9)$
$pH=6.9$ which is slightly less than the pH = 7 .