Answer:
4.84 m
Step-by-step explanation:
To solve this problem we need Frezing point depression.
Formula is: ΔT = Kf . m . i
ΔT = 18°C
This is data. ΔT is the difference, Freezing T° of pure solute - Freezing T° of solution.
Kf = 1.86 °C/m
m = molality. Our unknown.
i = Ions dissolved in solution, also called Van't Hoff factor.
NaCl → Na⁻ + Cl⁻
Sodium chloride can produce 2 moles of ions.
We replace data: 18°C = 1.86 °C/m . m . 2
18°C / (1.86 °C/m) . 2 = m
molality = 4.84