Question

Calculate the molarity of $11.7\%$ by mass of $NaCl$ in water. The density of the solution is $1.60g/mL$.
(Given, atomic mass $Na=23u,Cl=35.5u$)

• A. $1.6M$
• B. $4.2M$
• C. $3.2M$
• D. $2M$

Answer 1

The correct option is C $3.2M$

Asssuming $100g$ of the solution,
Mass of $NaCl=11.7g$
Molar mass of $NaCl=23+35.5=58.5g$
$\therefore$ Moles of $NaCl=\frac{11.7}{58.5}$ = 0.2
Mass of the solution = 100 g
Volume of the solution $=\frac{\text{Mass}}{\text{Density}}=\frac{100}{1.6}=62.5mL$

$\text{Molarity}=\frac{\text{moles}}{\text{volume (L)}}=\frac{0.2}{0.0625}=3.2M$