ou are asked to calculate the Kf for 5-butyl alcohol (MW = 74.122 g/mol). You ga

Question

ou are asked to calculate the Kf for 5-butyl alcohol (MW = 74.122 g/mol). You gather the following information in your experiment. You weigh out 2.124 g t-butyl alcohol and you determine the freezing point of the solvent t-butyl alcohol is 21.6 °C (freezing point pure t-butyl alcohol). You then add water to the test tube with the t-butyl alcohol and measure the freezing point to be 15.3 °C. What key piece of information are you missing to calculate the Kf? Question 4 options: A) mass of the solvent B) mass of the solute C) freezing point of the pure solvent D) freezing point of the solvent + the solute

Explanation / Answer

delta Tf = 21.6 - 15.3 = 6.3 oC
delta Tf = kf*m

To calculate Kf, we need to calculate molality, m
m = mass of solute / (molar mass of solute * mass of solvent in Kg)
mass of solute = missing
mass of solvent = 2.124 g
molar mass of solute = molar mass of water = 18 g/mol
Answer: B

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