Concentration of aqueous solutions

Exercise 5

    

Determine the number of moles of sodium hydroxide in $3050\;mL$ of a $21.90\%$ solution S, knowing its density $d_S$ $=$ $1.240$.

$d_S$ $=$ $1.240$ $\rho_S$ $=$ $1.240\frac{g}{mL}$ $\frac{m_S}{V}$ $=$ $1.240$ $m_S$ $=$ $1.240\cdot 3050$ $=$ $3782\; g$ $\%_{NaOH}$ $=$ $21.90$ $\frac{m_{NaOH}\cdot 100}{m_S}$ $=$ $21.90$ $m_{NaOH}$ $=$ $\frac{21.90\cdot 3782}{100}$ $=$ $827.8\; g$ $n_{NaOH}$ $=$ $\frac{m_{NaOH}}{M_{NaOH}}$ $=$ $\frac{827.8}{40}$ $=$ $20.7\cdot 10^1\;mol$