Question

The value for Kw is 1.0 x 10-14 at 298K, but this value is temperature dependent. Given what you know about Kw and acid/base chemistry, what will the pH of water be at 283K if the value for Kw is 0.29 x 10-14? Is this solution acidic, basic, or neutral?
a. pH = 7.26, acidic
b. pH = 7.26, neutral
c. pH = 7.00, neutral
d. pH = 14.54, basic
e. pH = 7.26, basic

Answer 1

Answer:

The correct answer is option b.

Explanation:

$H_2O\rightleftharpoons H^++OH^-$

The ionic product of water : $K_w$

$K_w=[H^+][OH^-]$

A pure water has equal concentration of hydrogen ions and hydroxide ions, hence neutral.

$K_w=[H^+][H^+]=[H^+]^2$

The ionic product of water at 283 K = $K_w=0.29\times 10^{-14}$

$K_w=[H^+]^2$

$0.29\times 10^{-14}=[H^+]^2$

$[H^+]=5.385\times 10^{-8} M$

The pH of the water at 283 k;

$pH=-\log [H^+]$

$=-\log[5.385\times 10^{-8} M]=7.26$

A pure water has equal concentration of hydrogen ions and hydroxide ions,So water will e neutral at this temperature also.

The correct answer is option b.