Question

Which of the following expression is not true

• A. $\left[H^{+}\right]=\left[O{H}^{-}\right]=\sqrt{K_w}$ for a neutral solution at all temperatures.
• B. $\left[H^{+}\right]>\sqrt{K_w}$ & $\left[O{H}^{-}\right]<\sqrt{K_w}$ for an acidic solution
• C. $\left[H^{+}\right]<\sqrt{K_w}$ & $\left[O{H}^{-}\right]>\sqrt{K_w}$ for an alkaline solution
• D. $\left[H^{+}\right]=\left[O{H}^{-}\right]={10}^{-7}M$ for a neutral solution at all temperatures.

Answer 1

The correct option is D $\left[H^{+}\right]=\left[O{H}^{-}\right]={10}^{-7}M$ for a neutral solution at all temperatures.

(A) For neutral water, $\left[H^{+}\right]=[OH{]}^{-}$
and $\left[H^{+}\right].[OH{]}^{-}=K_w\therefore [H^{+}{]}^2=\left[O{H}^{-}\right]=\sqrt{K_w}$
(B) In acidic solution $\left[H^{+}\right]>\left[O{H}^{-}\right]\left[H^{+}\right]\left[O{H}^{-}\right]=K_w\Rightarrow and\left[O{H}^{-}\right]<\sqrt{K_w}$
(C) For alkaline solution, $\left[O{H}^{-}\right]>\left[H^{+}\right]\therefore ,$
$\left[O{H}^{-}\right]>\sqrt{K_w}$ and $\left[H^{+}\right]<\sqrt{K_w}$
(D) As temperature $\uparrow$ pH $\downarrow$ hence, $\left[H^{+}\right]$ & $\left[O{H}^{-}\right]$ $\uparrow$ because dissociation of water $\uparrow$
But there is no change in neutrality of $H_{2}O$
So, $\left[H^{+}\right]=\left[O{H}^{-}\right]={10}^{-7}$ not true for all temperature.