We will be closed on August 21 to allow our employees to enjoy the Great American Eclipse.

Vernier Software and Technology
Vernier Software & Technology

Using Freezing-Point Depression to Find Molecular Weight

Figure from experiment 4 from Advanced Chemistry with Vernier

Introduction

When a solute is dissolved in a solvent, the freezing temperature is lowered in proportion to the number of moles of solute added. This property, known as freezing-point depression, is a colligative property; that is, it depends on the ratio of solute and solvent particles, not on the nature of the substance itself. The equation that shows this relationship is

\Delta t = {K_f} \times m

where Δt is the freezing point depression, Kf is the freezing point depression constant for a particular solvent (3.9°C•kg/mol for lauric acid in this experiment), and m is the molality of the solution (in mol solute/kg solvent).

Objectives

In this experiment, you will

  • Determine the freezing temperature of the pure solvent, lauric acid.
  • Determine the freezing temperature of a mixture of lauric acid and benzoic acid.
  • Calculate the freezing point depression of the mixture.
  • Calculate the molecular weight of benzoic acid.

Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

Option 1

Option 2

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

Standards Correlations

See all standards correlations for Advanced Chemistry with Vernier »

Experiment 4 from Advanced Chemistry with Vernier Lab Book

<i>Advanced Chemistry with Vernier</i> book cover

Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.

Buy the Book

Go to top

We will be closed on August 21 to allow our employees to enjoy the Great American Eclipse.