Answer to Question #186111 in General Chemistry for Adam LAquis

Question

Cyanic acid is a weak monoprotic acid. If the pH of 0.150 M cyanic acid is 2.32.Calculate Ka for cyanic acid.

Answer 1

$pH=2.32$

$pH=-log([H_3O^+])$

$log([H_3O^+])=-pH$

$10^{log([H_3O^+])}=10^{-pH}$

$([H_3O^+])=10^{-pH}$

$([H_3O^+])=10^{-2.32}=4.8×10^{-3}M$

$[A^-]=([H_3O^+])$ Produced in 1:1 mole

$[A^-]=4.8×10^{-3}M$

$HA=0.150-[4.8×10^{-3}]$

$HA=0.1452M$

$K_a=\frac{[A^- ]× [H_3O^+]}{[HA]}$

$K_a=\frac {[4.8×10^{-3}]^2}{0.1452}$

$K_a= 1.6 ×10^{-4}M$