pH of acids, bases and salts

Exercise 17

    

Calculate the mass of sodium hydroxide that must be dissolved in a volumetric flask $J$ of 1000 $mL$ in order to obtain a solution with $pH$ = 12.9.

$NaOH$: strong base Final solution: $pH$ $=$ $14$ $+$ $log\;[OH^-]$ $[OH^-]$ $=$ $10^{pH-14}$ = 0.08 $\frac{mol}{L}$ $c_{NaOH}$ $=$ $\frac{0.08}{1}$ $n_{NaOH}$ = $c_{NaOH}\cdot V_{J}$ = 0.08$\cdot$1 = 0.08 $\;mol$ $m_{NaOH}$ = $n_{NaOH}\cdot M_{NaOH}$ = 0.08$\cdot$40.01 = 3.201$\; g$