Calculate the volume of a 30 % ($\rho_S=$ 1.1492 $\frac{g}{mL}$) solution $S$ of chlorhydric acid
that must be diluted in a volumetric flask $j$ of 250 $mL$ in order to obtain a solution with $pH$ = 2.81
$HCl$: strong acid
Final solution:
$c$ $=$ $10^{-pH}$ =
$10^{-2.81}$ =
0.15 $\frac{mol}{L}$
$n_{HCl}$ =
$c_{HCl}\cdot V_{j}$ =
0.15$\cdot$0.25 =
0.0375$\;mol$
The initial concentrated solution had the same number of moles:
Initial solution $S$:
$m_{HCl}$ =
$n_{HCl}\cdot M_{HCl}$ =
0.0375$\cdot$36.47 =
1.368$\;g$
$m_S$ =
$\frac{m_{HCl}\cdot 100}{\%_S}$ =
$\frac{1.368\cdot 100}{30}$ =
4.56$\;g$
$V_S$ =
$\frac{m_S}{\rho_S}$ =
$\frac{1.368}{1.1492}$ =
1.19$\;mL$
