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Why salt the roads?

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Keywords: chemistry, science, colligative properties, vernier, technology, environment, cost effective
Subject(s): Chemistry
Grades 10 through 12
NETS-S Standard:
  • Creativity and Innovation
  • Communication and Collaboration
  • Research and Information Fluency
  • Critical Thinking, Problem Solving, and Decision Making
  • Technology Operations and Concepts
View Full Text of Standards
School: Woodstock High School, Woodstock, IL
Planned By: Tressa Sharma
Original Author: Tressa Sharma, Woodstock
Investigation Questions
During the winter in the state of Illinois we salt the roads, but why? Many people respond that it melts the ice, but how does it do that? Is one salt better than the other, and if so why? Are there any environmental impacts on our salting roads and is there a more efficient way to make the roads safe during the winter?

Pre-lab Investigation

Not every state or even county in Illinois uses the same salt for their roads. For the pre-lab investigation you need to complete a short research paper, no longer than 2 pages, single-spaced, 12 point font, describing three different salts, substances, or techniques used to make icy roads safe. In your research you need to include at least five pros and five cons for each icy road prevention discussed. Be sure to cite all your sources.

Lab Investigation

You will now be collecting data on different salts that can be used for icy road prevention. You will collect the data on how the boiling point and freezing point of water changes with added solutes. The materials for this lab are listed below:
Vernier Temperature Probe
Vernier Labquest 2
Ring stand
Hot plate
Clamps x 2
250 mL beaker
Sodium chloride, NaCl
Calcium chloride, CaCl2
Magnesium chloride, MgCl2
Aluminum chloride, AlCl3
Digital scale
Stirring rod

Boiling Point Investigation
You will collect data on the boiling point for when each of the salt solutions (NaCl, CaCl2, MgCl2, and AlCl3) is dissolved in water. For each salt follow the procedure below.
Get goggles from the goggle cabinet. Always wear goggles in the lab.
Connect the temperature probe to the Labquest2 and set the data to be collected for 900 seconds.
Place the hot plate on the ring stand or next to the ring stand.
Fill the 250 mL beaker with 175 mL of distilled water. Add 15 grams of salt and stir to dissolve. Place the beaker on the hot plate.
Suspend the temperature probe in the beaker using a clamp. Make sure that the temperature probe is not touching the bottom or sides of the beaker.
Turn on the hotplate to medium-high heat and begin recording data. Data collection will occur for 900 seconds.
Once the data collection has completed turn off the hotplate and let the beaker cool. It will be extremely hot so do not touch it. Once the beaker has cooled you can discard the solution per your teacher's directions.
Repeat steps 4 - 7 for each salt listed.

Freezing Point Investigation
You will collect data on the boiling point for when each of the salts is added to crushed ice. Follow the procedure below for each salt.
Get goggles from the goggle cabinet. Always wear goggles in the lab.
Use the same setup from the boiling point investigation but remove the hotplate.
Fill the 250 mL beaker approximately ĺ of the way full with crushed ice.
Place the temperature probe in the crushed ice. Be sure it is fully submerged in the ice and that it is not touching the beaker. Begin recording data.
Add 15 grams of salt to the ice and gently stir using the glass stirring rod. Be sure to not hit or bump the temperature probe. After a minute or so of stirring you may stop.
Once the data collection has completed remove the temperature probe from the crushed ice and wipe off. Discard the ice mixture per your teacherís directions.
Repeat steps 3 - 6 for each salt listed.

Post-lab Analysis
Based on your data collection answer the following questions.

Which salt had the greatest affect on the boiling point? Why?
Which salt had the greatest affect on the freezing point? Why?
Some stores sell bags of ice salt that contain both calcium chloride and magnesium chloride, why do you think they have a mixture of the two salts? How does mixing the salts more beneficial than using one salt?
Give 5 real world examples where the boiling point or freezing point of water is altered using solutes.

You and your lab partner have been tasked by the city to analyze the different options for salting the roads in the winter. You must create a presentation on which salt is best to use and why. Keep in mind the city wants to find the most cost effective and environmentally safe method for keeping the roads safe. You may use posters, videos, PowerPoint presentations, animations, etc. for your presentation.
This lesson is just one example of the many different inquiry activities they can do with this equipment. Equipment used in laboratories around the world is becoming more digital and advanced. With this equipment I will be preparing my current and future students to be college and career ready in the field of science.
Cross-Curriculum Ideas
This lesson not only has students focusing on chemistry but also their environment, road safety, economics, and how cities make choices that benefit their community.
One follow-up activity for this lesson would be for students to conduct research on what is currently being used in our community. If we determine that there are better options during our lesson I will have students write to the local government with their findings and suggestions on how we can improve our communities safety, environment, and economics by simply changing how we salt our roads in the winter.
Materials: Mobile Labs, Electronics
Other Items: 6 LabQuest2 Advanced Chemistry Package, $1265 each, total of $7590.00
6 Electrode Support, $10 each, total of $60.00
1 Chemistry Investigations for use with AP Chemistry, $48 each, total of $48.00
1 Advanced Chemistry with Vernier, $48 each, total of $48.00
1 Investigating Chemistry Through Inquiry, $48 each, total of $48.00
1 Plastic Cuvettes, $99 each, total of $99.00