Exploring Freezing Point Depression using Freeze Pops
This lab is designed to familiarize students with freezing point depression. When a nonvolatile solute (such as salt) is added to a solid, it causes the point of freezing to drop. Compounds that break into ions when dissolving are better at lowering the freezing point than substances that do not separate into particles because the added particles disrupt the ability of the water to form crystalline ice. The more particles there are, the greater the disruption and the greater the impact on particle-dependent properties such as the freezing point. In this lab, students will add salt to ice. They will record the time and temperature data and interpret their results. They will then compare their data to that of their classmates.
- Students will collaborate with other groups to gather and arrange data pertaining to the temperature of each groups system.
- Upon completion of the initial exercise, students will use their lab experience to explain the concept of freezing point depression and relate their findings to other colligative properties.
- Students will relate their findings to everyday situations such as using salt to clear icy side walks and to determine which material is best suited for use by highway departments to de-ice roads and bridges
Context for Use
Resource Type: Activities:Lab Activity
Grade Level: High School (9-12)
Description and Teaching Materials
I use this activity as an introduction to colligative properties. The students have not had any background information pertaining to this topic. They have, however, talked about interaction of solute and solvent particles when making a solution. They are also familiar with polarity, ionic and covalent bonds.
The second day of class is spent sharing data. A large data table is projected on the board and lab groups enter their data to share with each other. Each group now has a large collection of data to help them evaluate the effect of varying amounts of salt on the temperature of the ice/water. A significant portion of the second day is spent discussing what really happened during the activity. This discussion happens before the students write their conclusion for the lab. They're graded on the content of their conclusion. If they benefited from the group discussion, it will be evident in their conclusion as this is their chance to tell exactly how much they understand about what happened. Please see the lab hand out associated with this activity in the "attachments" section. Student Hand Out for Freezing Point Depression Lab (Microsoft Word 31kB Aug16 09)
Teaching Notes and Tips
- 220.127.116.11.2 – develop possible solutions to an engineering problem and evaluate them using conceptual and mathematical models.
- 18.104.22.168.3 – Select and use appropriate numeric, symbolic, pictorial, or graphical representation to communicate scientific ideas, procedures, and experimental results.
- 22.214.171.124.4 – Relate exothermic and endothermic reactions to temperature and energy changes
- 9.C.126.96.36.199 – Describe dynamic processes by which solutes dissolve in solvents
- 9C. 188.8.131.52 – Use kinetic molecular theory to explain how changes in energy content affect the state of matter.