Answer
a. $pH\approx 2.3$
b. $pH\approx 3.5$
c. $pH\approx 8.3$
Work Step by Step
(see p.381)
The $\mathrm{p}\mathrm{H}$ scale measures the acidity of a solution:$ \quad \mathrm{p}\mathrm{H}=-\log[\mathrm{H}^{+}]$
where $[\mathrm{H}^{+}]$ is the hydrogen ion concentration (in moles per liter, M).
Solutions are
neutral if $pH=7$
acidic if $pH < 7$
basic if $pH > 7$
------------------
a.
$pH=-\log[\mathrm{H}^{+}]=-\log(5.0\times 10^{-3})\approx 2.3$
b.
$pH=-\log(3.2\times 10^{-4})\approx 3.5$
c.
$pH=-\log(5.0\times 10^{-9})\approx 8.3$