Question

The molality of $2$% $\left(W/W\right)NaCl$ solution is nearly

• A. $0.02m$
• B. $0.35m$
• C. $0.25m$
• D. $0.45m$

Answer 1

The correct option is B $0.35m$

2% NaCl means 2 grams NaCl present in 100 grams solution.

Mass of solution is the sum of masses of solute and solvent. Our solute is NaCl and the solvent is water.

mass of solvent $=$ mass of solution - mass of solute

molality is the moles of solute per kg of solvent.

Moles of NaCl could be calculated on dividing it's grams by it's molar mass(58.44).

moles of NaCl = $2g\times \frac{1}{58.44}$ = $0.034moles$

molality of solution = $\frac{0.034}{0.098}$

molality of solution = $0.35m$

mass of solvent = $100-2=98g=0.098kg$

2 % NaCl molality is $0.35m.$

Hence, option B is correct.