Question

The molality and molarity of a solution of glucose in water which is labeled as 10% (w/w) are respectively (density of solution = 1.2 g/mL)

• A. 0.57 m, 0.517 M
• B. 0.67 m, 0.61 M
• C. 0.611 m, 0.67 M
• D. 0.517 m, 0.57 M

Hint:

Use density to find volume when mass is known
Molality = moles per kg of solvent, Molarity = moles per liter of solution

Answer 1

The Correct Option is C

Assume 100 g of solution: - Glucose = 10 g - Water = 90 g = 0.090 kg Molality: \[ \text{Mol. mass of glucose} = 180 \text{ g/mol},\quad \text{mol} = \frac{10}{180} = 0.0556 \] \[ m = \frac{0.0556}{0.090} \approx 0.617 \approx 0.611 \text{ mol/kg} \] Molarity: \[ \text{Volume} = \frac{100}{1.2} = 83.33 \text{ mL} = 0.08333 \text{ L} \] \[ M = \frac{0.0556}{0.08333} \approx 0.67 \text{ mol/L} \]