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Created by LABScI at Stanford
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Freezing Point Depression: Can oceans freeze?
Teacher Version
Freezing point depression describes the process where the temperature at which a liquid freezes is
lowered by adding another compound. It depends only on the number of dissolved particles in solution.
This is known as a colligative property. For example, water freezes at 0°C, but when a solute such as
salt or sugar is added to a solvent (water), the freezing point decreases. In order to see the freezing point
depression of saltwater and how it changes with varying amounts of solute concentration, you will use 5
cups with water and varying amounts of salt and measure each individual temperature. Then, using the
volume of the water and the volume of the solute, you will find the concentration of the solution. In the
second part of the lab, you will use two freezer bags to observe how readily water freezes when
surrounded by saltwater.
California Science Content Standards:
• 3. Conservation of Matter and Stoichiometry: The conservation of atoms in chemical
reactions leads to the principles of conservation of matter and the ability to calculate the
mass of products and reactants.
• 6. Solutions: Solutions are homogeneous mixtures of two or more substances.
• 6a. Students know the definitions of solute and solvent.
• 6c. Students know temperature, pressure, and surface area affect the dissolving process.
• 6d. Students know how to calculate the concentration of a solute in terms of grams per liter,
molarity, parts per million, and percent composition.
• **6e. Students know the relationship between the molality of a solute in a solution and the
solution's depressed freezing point or elevated boiling point.
• 7. Chemical Thermodynamics: Energy is exchanged or transformed in all chemical reactions
and physical changes of matter.
• 7a. Students know how to describe temperature and heat flow in terms of the motion of molecules
(or atoms).
Key Concepts:
• A solution is a mixture composed of two or more substances. In a solution, the solute dissolves
into another substance, referred to as the solvent.
• A solution’s colligative properties refer to the number of dissolved particles contained in the
solution and are not dependent on the identity of the solutes.
• A solution’s concentration refers to the amount of solute mixed in with the solvent (e.g.10%
saline solution).
• When water freezes, energy is released in the form of heat. This is why ice has a lower
temperature than water. When ice melts, energy is absorbed, increasing the temperature.
Materials (Part 1):
• 5 foam cups
• Water
• Ice
• Salt and sugar
• Thermometer
• 100mL graduated cylinder
• Measuring cup
• 1 tablespoon and teaspoon
• Access to the Periodic Table of Elements
• Stirring rod
• Strainer
• Graph paper (if available)
