A solution contains 15.5 g of NaOH dissolved in sufficient water to give a total mass of 125.0 g. What is the molality of the solution?
A)3.54 m
B)0.124 m
C)0.00310 m
D)3.10 m
E)124 m

Question

Quizplus · Accepted Answer

Molality is calculated as moles of solute per kilogram of solvent. First, calculate the moles of NaOH: $ \frac{15.5 \, \text{g}}{39.997 \, \text{g/mol}} = 0.3875 \, \text{mol} $. The mass of the solvent (water) is $ 125.0 \, \text{g} - 15.5 \, \text{g} = 109.5 \, \text{g} = 0.1095 \, \text{kg} $. Molality = $ \frac{0.3875 \, \text{mol}}{0.1095 \, \text{kg}} = 3.54 \, \text{m} $.

A Solution Contains 15