5 Steps to a 5 AP Chemistry

314  STEP 5. Build Your Test-Taking Confidence

Question 3.

The following materials are made available for the determination of the molar mass of an unknown non-

volatile solid.

analytical balance thermometer beaker support stand and clamp

test tube stopwatch hot plate

Phenol (melting point = 43 °C and Kf=7.40°C/m) is available as the solvent. The unknown behaves as a

nonelectrolyte in phenol.

(a) Plot a cooling curve for phenol on the axes below, and plot the cooling curve for a solution of the

unknown in phenol.

(b) What information must be obtained from the two graphs in order to calculate the molar mass?

(c) What additional information is needed to determine the molar mass of the unknown solid?

(d) Show how the above information may be used to calculate the molar mass of the unknown solid.

STOP

Pure Phenol: Solution:

43 °C

Time

43 °C

Time