pH of acids, bases and salts
Exercise 17

Calculate the mass of potassium hydoxide that must be dissolved in a volumetric flask $J$ of 500 $mL$ in order to obtain a solution with $pH$ = 12.48.
$KOH$: strong base
Final solution:
$pH$ $=$ $14$ $+$ $log\;[OH^-]$
$[OH^-]$ $=$ $10^{pH-14}$ =
0.03 $\frac{mol}{L}$
$c_{KOH}$ $=$ $\frac{0.03}{1}$
$n_{KOH}$ =
$c_{KOH}\cdot V_{J}$ =
0.03$\cdot$0.5 =
0.015 $\;mol$
$m_{KOH}$ =
$n_{KOH}\cdot M_{KOH}$ =
0.015$\cdot$56.11 =
0.842$\; g$