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 $pH$ = 12.3.

$NaOH$: strong base Final solution: $pH$ $=$ $14$ $+$ $log\;[OH^-]$ $[OH^-]$ $=$ $10^{pH-14}$ = 0.02 $\frac{mol}{L}$ $c_{NaOH}$ $=$ $\frac{0.02}{1}$ $n_{NaOH}$ = $c_{NaOH}\cdot V_{J}$ = 0.02$\cdot$1 = 0.02 $\;mol$ $m_{NaOH}$ = $n_{NaOH}\cdot M_{NaOH}$ = 0.02$\cdot$40.01 = 0.8$\; g$