MHS AP Chemistry
Colligative Properties and Molecular Weight #2


The purpose of this activity is to determine the molecular weight of an unknown substance by measuring the boiling point elevaion produced in a known solvent. The molecular weight will be used to identify the unknown substance.

  1. The solvent is zzzzzz. The boiling point elevation constant for this substance is k = xx.x C°/m. The solute will be announced in class.
  2. Measure the mass and boiling point of zzzzzzz.
  3. Add some of the unknown solute (no more than about 1/20th of the solvent mass). Measure the new boiling point, and determine the mass of unknown added.
  4. Use the formula DT = kfm [eq. 13.12] and the definition of molality to calculate the molecular weight of the unknown solute.
  5. Use the measured molecular weight of your unknown to identify it from the following list: a, b, c, d, e, f, or g.
  6. Look up the actual boiling point of pure zzzzzz.

Write Up

This lab is due on ______________. .

[Syllabus 13][MHS AP Chem page]