Question

A solution contains 29.25 g of NaCl in 500 mL of the solution. Which of the following statements is/are true? (Molar mass of NaCl = 58.5 g/mol)

• A. It's molarity is 1 M
• B. It's molality is 1m if the density of the solution is 1.0585 g/mL
• C. w/V % of the solution is 5.85%
• D. w/w % of the solution is 5.85%

Answer 1

Answer: (A), (B), (C)

w/V % of the solution is 5.85%

(a) Molarity $=\frac{\text{number of moles of the solute}}{\text{Volume of the solution in litre}}$

Number of moles of NaCl$=\frac{\text{mass of NaCl}}{\text{Molar mass of NaCl}}=\frac{29.25}{58.5}=0.5$

Molarity $=\frac{0.5}{0.5}=1M$

(b) Molality $=\frac{\text{Moles of the solute}}{\text{Mass of the solvent in kg}}$

mass of the solution = volume x density $=500\times 1.0585=529.25g$

Mass of the solvent = 500 g
Molality $=\frac{0.5}{0.5}=1$ m

$\left(c\right)\frac{w}{v}\%=\frac{\text{Mass the solute}}{\text{Volume of the solution}}\times 100$
$=\frac{29.25}{500}\times 100$
= 5.85%

(d) Density is not given. Hence, the mass of the solution cannot be calculated.