A laboratory reference book lists the following values of the ion-product constant…

CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases

Problem

A laboratory reference book lists the following values of the ion-product constant for water:

Temperature $(^\circ\!\text{C})$	$K_w$
$20$	$6.8\times10^{-15}$
$30$	$1.5\times10^{-14}$
$40$	$2.9\times10^{-14}$

A student needs the neutral pH of water at

35^\circ\!\text{C}

for a simulation, but the value is not tabulated. (a) Using an appropriate numerical method, estimate

K_w

35^\circ\!\text{C}

. Clearly outline your reasoning and any assumptions. (b) From the value obtained in part (a), determine the pH of neutral water at

35^\circ\!\text{C}

. (c) Suppose the student mistakenly used the

30^\circ\!\text{C}

value of

K_w

instead of the estimated

35^\circ\!\text{C}

value. Calculate the resulting percent error in the neutral pH and comment on whether the approximation would be acceptable in routine laboratory work.

Related theory

Browse the problem library