Question

Assertion (A): pH of pure water increases with increase in temperature. Reason (R): Self ionization of water is an endothermic reaction. Which of the following is correct?

• A. Both A & R are correct and R is correct explanation of A.
• B. Both A & R are correct but R is not a correct explanation of A.
• C. A is true but R is false
• D. A is false but R is true.

Answer 1

The correct option is D A is false but R is true.

Self ionization of water is an endothermic reaction-
$H_{2}O\left(l\right)\leftrightharpoons H^{+}\left(aq\right)+O{H}^{-}\left(aq\right)△H>0$
Thus R is correct.
$pH=-log\left[H^{+}\right]=-log\sqrt{K_w}$
As forward reaction is endothermic,values of $K_w$ will increase on increasing the temperature.Hence pH will decrease.Thus A is false.