Alternative Deicers: An Application of Freezing Point Depression

Jennie Mayer and Daniel Mitchell, Bellevue Community College

Summary

The use of deicers on U.S. roads and highways raise several environmental and cost concerns, include the alteration and degradation of habitats, contamination of groundwater aquifers, and the corrosion of automobiles and highways. In this activity, students will consider alternatives to current deicer while investigating colligative properties. Students will expand their chemical knowledge by (1) researching the environmental side effects and costs of various solutes as potential alternatives, (2) using an online simulation to learn about concentration and the van't Hoff factor, and (3) conducting an experiment of their own design that provides some support for their alternative. A summary of these findings and rationale for an alternative deicer will be in the form of a proposal to the city mayor.

Learning Goals

The learning outcomes for this project are as follows:

  • Students will research the current method/materials used for deicing roads in Washington State and articulate the environmental and cost issues involved.
  • Students will be able to predict the van't Hoff factor and freezing point depression for different solutes.
  • Students will communicate (in simple and easy-to-understand explanations) what freezing point depression is and how it occurs on the molecular level.
  • Students will consider other physical and chemical phenomena, such as the heat of solution and solubility, in their choice of a deicer, by obtaining experimental data from a handbook or by their own experiments.
  • Students will design and carry out an experiment, the results of which will help them make decisions on the best alternative deicer.
  • Students will be able to present a case for their alternative deicer based on research and experimental evidence.

Context for Use

This activity would work in an environmental sciences discipline.

This project takes one or two lab periods, and potentially one discussion period. The students may perform the majority of the project outside of class, but the heat of solution, freezing point depression, and solubility tests need to be performed in a lab environment. If time outside of class is not feasible for students, then two discussion periods may be needed.

Description and Teaching Materials

The purpose of this activity is to further student understanding of a colligative property through a real-world practical issue. This project will reinforce the topics of freezing point depression, molality, and van't Hoff factor learned in a typical general chemistry course.

State and local highway agencies spend about $300 million on the purchase of deicing chemicals, and another $250 million on their storage, handling, and application.2 This price tag does not include the environmental or societal cost of using deicers on U.S. roads and highways. In addition to the corrosion of automobiles and highways, runoff from deicers can degrade habitats by stressing native plants and aquatic life. Runoff can also cause contamination of groundwater and soil. Alternatives to salt have been studied for the past 40 years, and include non-chloride salts and organic substances, such as calcium magnesium acetate and propylene glycol.

The use of deicers on U.S. roads and highways raise several environmental and cost concerns, include the alteration and degradation of habitats, contamination of groundwater aquifers, and the corrosion of automobiles and highways. In this activity, students will consider alternatives to current deicer while investigating colligative properties. Students will expand their chemical knowledge by (1) researching the environmental side effects and costs of various solutes as potential alternatives, (2) using an online simulation to learn about concentration and the van't Hoff factor, and (3) conducting an experiment of their own design that provides some support for their alternative. A summary of these findings and rationale for an alternative deicer will be in the form of a proposal to the city mayor.

The tasks that the students will be asked to perform are varied and diverse:

  1. Research background information about the environmental and cost issues involved with deicing roads and what is currently used in our bioregion;
  2. Investigate the causes of freezing point depression and the difference in magnitude of the effect based on the identity of the solute by using an online simulation;
  3. Perform an experiment that helps to narrow down a list of alternative deicers based on cost and effectiveness; and,
  4. Summarize findings in a format that is targeted to the lay public and provides rationale for an alternative deicer (or to support that the current deicer is the best choice).


A Proposal for the Best Deicer (Microsoft Word 46kB Oct31 11)

Teaching Notes and Tips

There are no "perfect" colligative property simulations available on the Web. Many can be misleading as they indicate that steric effects are a contributing factor. It would be worthwhile for the students to discuss the pros and cons of various simulations that are shown on the Web that describe colligative properties, if time permits. This will strongly reinforce the students understanding of what causes colligative properties in the first place.

Instructors using this project may find it beneficial to discuss parts 1, 2, and 4 in class; discussion in class is not required for the project to be a success. The project is designed to be able to be done largely by groups of students on their own. Part 3 however must be performed in class or lab.

Assessment

References and Resources

In part one of the activity, students are tasked with researching background information regarding the effects of various solutes used in deicing roads. The resources needed for this research include: library material, instructor provided peer-reviewed publications, Internet resources, academic texts, and appropriate television programs on video. To encourage students to conduct research, we have not provided any specific references (we may need to provide some guidance for students in conducting research at the library). Alternatively, you can provide students with specific resources. Another part of the activity requires a simulation on the Internet:

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/propOfSoln/colligative.html.

Alternatives to deicing roads (Virginia Tech): http://www.webapps.cee.vt.edu/ewr/environmental/teach/gwprimer/group05/altern.html

Evergreen State College