Answer
(a) $[\mathrm{H}^{+}]=10^{-4.6}\ \mathrm{M}\approx 2.5\times 10^{-5}\ \mathrm{M}$
(b) $5.0\times 10^{-8}$ M
Work Step by Step
(a)
We are given:
$\mathrm{p}\mathrm{H}=-\log[\mathrm{H}^{+}]=4.6$
Therefore:
$[\mathrm{H}^{+}]=10^{-4.6}\ \mathrm{M}\approx 2.5\times 10^{-5}\ \mathrm{M}$
(b)
We are given:
$\mathrm{p}\mathrm{H}=-\log[\mathrm{H}^{+}]=7.3$
Therefore:
$[\mathrm{H}^{+}]=10^{-7.3}\ \mathrm{M}\approx 5.0\times 10^{-8}\ \mathrm{M}$