Solute A associates in water. When 0.7 g of solute is dissolved in 42 g of water, it depresses the freezing point by 0.2oC. What is the percentage association of solute A in water? (Given: Molar mass of A = 93 g/mol, Kf = 1.86 K kg/mol)
Answer & explanation
Correct answer: option 4
Since, ΔTf = i Kf m
m = \(\frac{0.7}{93}\) x \(\frac{1000}{42}\)
0.2 = i x 1.86 x \(\frac{0.7}{93}\) x \(\frac{1000}{42}\)
i = 0.6
α = \(\frac{i - 1}{\frac{1}{n} - 1}\)
α = \(\frac{0.6 - 1}{\frac{1}{2} - 1}\) = 0.8
Hence, percentage association of solute is 80%.