Question

What is the molar mass of a covalent compound if 0.486 g of it is dissolved in 25.0 ml of water and produces a freezing temperature of -0.40 °c?

Answer 1

Answer is: the molar mass of a covalent compound is 90.4 g/mol.

m(compound) = 0.486 g.
m(water) = 25 mL · 1 g/mL = 25 g ÷ 1000 g/kg = 0.025 kg.
ΔT = 0°C - (-0.40°C) = 0.40°C.

Kf(H₂O) = 1.86°C/m.

M(compound) = Kf · m(compound) / m(water) · ΔT.
M(compound)= 1.86°C/m · 0.486 g / (0.025 kg · 0.4°C).
M(compound) = 90.4 g/mol.