Solute A associates in water. When 0.7 g of solute A is dissolved in 42.0 g of water, it depresses the freezing point by 0.2°C. The percentage association of solute A in water, is

[Given: Molar mass

Question

Solute A associates in water. When 0.7 g of solute A is dissolved in 42.0 g of water, it depresses the freezing point by 0.2°C. The percentage association of solute A in water, is

[Given: Molar mass of A = 93 g mol⁻¹. Molal depression constant of water is 1.86 K kg mol⁻¹]

Canvas Classes · Accepted Answer

Strategy:
 Association leads to a decrease in the number of particles (). Calculate the actual molality from , compare it to the expected molality to find , and solve for the degree of association .

Step 1: Calculate expected molality ()
- Mass of A = 0.7 g, Molar mass = 93 g/mol.
- Mass of water = 42 g = 0.042 kg.

Step 2: Calculate observed molality ()
, .

Step 3: Determine van't Hoff factor ()

Step 4: Solve for association
Assuming dimerization (): .

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