pH of acids, bases and salts
Exercise 17

Calculate the mass of sodium hydroxide that must be dissolved in a volumetric flask $J$ of 250 $mL$ in order to obtain a solution with $pH$ = 13.18.
$NaOH$: strong base
Final solution:
$pH$ $=$ $14$ $+$ $log\;[OH^-]$
$[OH^-]$ $=$ $10^{pH-14}$ =
0.15 $\frac{mol}{L}$
$c_{NaOH}$ $=$ $\frac{0.15}{1}$
$n_{NaOH}$ =
$c_{NaOH}\cdot V_{J}$ =
0.15$\cdot$0.25 =
0.0375 $\;mol$
$m_{NaOH}$ =
$n_{NaOH}\cdot M_{NaOH}$ =
0.0375$\cdot$40.01 =
1.5$\; g$