Concentration of aqueous solutions

Exercise 11

    

An $35.0\%$ perchloric acid $HClO_4 $ solution S has a volumic mass of $1.251\frac{g}{cm^3}$. Calculate the molarity

Let's take for example $1L$ of S. $m_S$ $=$ $\%_S\dot V_S$ $=$ $1.251\cdot 1000$ $=$ $1251\;g$ $m_{HClO_4}$ $=$ $\frac{\%_S\cdot m_S}{100}$ $=$ $\frac{35.0 \cdot 1251}{100}$ $=$ $437.9 \;g$ $n_{HClO_4}$ $=$ $\frac{m_{HClO_4}}{M_{HClO_4}}$ $=$ $\frac{437.9}{100.5}$ $=$ $4.36 \;mol$ $c_{HClO_4}$ $=$ $\frac{n_{HClO_4}}{V_S}$ $=$ $\frac{4.36}{1}$ $=$ $4.36 \;M$