A solution made by dissolving 9.81 g of a nonvolatile nonelectrolyte in 90.0 g of water boiled at 100.37degree C at 760 mm Hg. What is the approximate molecular weight of the substance? (For water, Kb = 0.51 degree C/m)

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Ruchus

Chemistry

28 August, 13:44

A solution made by dissolving 9.81 g of a nonvolatile nonelectrolyte in 90.0 g of water boiled at 100.37degree C at 760 mm Hg. What is the approximate molecular weight of the substance? (For water, Kb = 0.51 degree C/m)

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Bruno Andrade · Answer 1

Answer is: molecular weight of the substance is 79.75 g/mol.

Kb (H ₂O) = 0,51°C / m.

T (nonvolatile nonelectrolyte) = 100.37 °C.

T (H ₂O) = 100°C.

ΔT = 100.37°C - 100°C.

ΔT = 0.37°C.

ΔT = b (nonvolatile nonelectrolyte) · Kb (H₂O).

b (nonvolatile nonelectrolyte) = ΔT : Kb (H₂O).

b (nonvolatile nonelectrolyte) = 0.37°C : 0.51°C/m.

b (nonvolatile nonelectrolyte) = 1.372 mol/kg.

b - molal concentration.

b = n (nonvolatile nonelectrolyte) / m (H₂O).

n = 1.372 mol/kg · 0.09 kg = 0.123 mol.

M (nonvolatile nonelectrolyte) = m / n.

M = 9.81 g : 0.123 mol = 79.75 g/mol.