Answer
(a) $[\mathrm{H}^{+}]=10^{-3}\ \mathrm{M}$
(b) $[\mathrm{H}^{+}]=10^{-6.5}\approx 3.2\times 10^{-7}\ \mathrm{M}$
Work Step by Step
(a)
We are given:
$\mathrm{p}\mathrm{H}=-\log[\mathrm{H}^{+}]=3.0$
Therefore:
$[\mathrm{H}^{+}]=10^{-3}\ \mathrm{M}=0.001\ \mathrm{M}$
(b)
We are given:
$\mathrm{p}\mathrm{H}=-\log[\mathrm{H}^{+}]=6.5$
Therefore:
$[\mathrm{H}^{+}]=10^{-6.5}\approx 3.2\times 10^{-7}\ \mathrm{M}$
