Name_______________________________________
Date_______________
It’s All about the Particles
Background
Freezing point depression is a colligative property which means that the freezing point depression is
related in some way to the number of particles in the solution. The number of particles can be affected
by changing the concentration of the solution. The number of particles can also be affected by the
number of particles formed when a substance dissociates in solution. Soluble molecular compounds do
not dissociate in aqueous solutions. On the other hand, soluble ionic compounds do dissociate in
aqueous solutions. The number of particles formed is related to the number of ions formed when the
solute dissociates.
In the investigation “How Cold is Freezing?,” you followed a procedure to find the freezing point
depression of a solute. Your task in this laboratory investigation is to explore the relationship between
the number of particles and the corresponding freezing point depression.
Objectives
1. After completing this laboratory investigation, the student will be able to determine the freezing
point depression of various solutes.
2. After completing this laboratory investigation, the student will be able to describe the relationship
of the number of particles in solution to the freezing point depression of various solutes.
3. After completing this laboratory investigation, the student will be able to describe the relationship
of molal concentration to the freezing point depression of various solutes.
Problem Statement
Determine the relationship between the number of particles of a solute in aqueous solution and the
freezing point depression of that solute.
Guidelines
The substances to be used for this laboratory investigation can be selected from the following
compounds: glucose, sucrose, sodium chloride, calcium chloride, magnesium chloride, potassium
acetate, and aluminum chloride. You are to select four solutes and explore three different
concentrations of each solute not to exceed 0.50 m.
Procedure
1. Devise a process to complete the investigation of the problem.
2. Complete a rough draft of 3:a-f below with any appropriate data tables and submit it to be
approved for experimentation.
3. Complete the laboratory work.
Name_______________________________________
Date_______________
4. Once you have completed the investigation, each group will need to complete a formal
laboratory report consisting of the following:
a. Title
b. Problem Statement
c. Hypotheses (related to objectives 2 and 3 above)
d. Independent and Dependent Variables
e. Materials/Equipment List
f. Procedure
g. Data: Qualitative (observations) and Quantitative (numerical)
h. Calculations
i. Conclusions and Evaluation; Be sure to address the following questions:
i. What conclusion can you make about the relationship between the number of
particles in a substance and its freezing point depression?
ii. What conclusion can you make about the relationship between the molal
concentration of a solution and the lowering of a solute’s freezing point?
iii. If able to complete the investigation again, what changes to your procedure
would you make to improve your results?