pH of acids, bases and salts

Exercise 17

    

Calculate the mass of calcium hydroxide that must be dissolved in a volumetric flask $J$ of 1000 $mL$ in order to obtain a solution with $pH$ = 12.7.

$Ca(OH)_2$: strong base Final solution: $pH$ $=$ $14$ $+$ $log\;[OH^-]$ $[OH^-]$ $=$ $10^{pH-14}$ = 0.05 $\frac{mol}{L}$ $c_{Ca(OH)_2}$ $=$ $\frac{0.05}{2}$ $n_{Ca(OH)_2}$ = $c_{Ca(OH)_2}\cdot V_{J}$ = 0.025$\cdot$1 = 0.025 $\;mol$ $m_{Ca(OH)_2}$ = $n_{Ca(OH)_2}\cdot M_{Ca(OH)_2}$ = 0.025$\cdot$74.09 = 1.852$\; g$