Question

The weak acid HQ has pKa of 4.89. Calculate the (OH-) of 0.500 M HQ

Answer 1

First find \([H^+]\), then use \(\sf [H^+][OH^-]=K_w=1.0*10^{-14}\)

Answer 2

\[pKa = -\log Ka => Ka = 10^{-pKa}\]
\[[H ^{+}]= \sqrt{Ka \times Ca}\]

where Ca is the initial concentration of the acid assuming that the "x too small"