Learning Library

# An Alternative to Road Salt

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The goal of this project is to have the student evaluate an alternative method for melting roadway ice by conducting a formal scientific investigation.

• Bulleted list of questions to be asked
• What is the relative effectiveness of rock salt, beet juice, and a mixture of rock salt and beet juice in causing ice to melt?
• Does beet juice prevent corrosion by blocking the distribution of chloride ions?

In colder parts of the country, rock salt (whose main ingredient is sodium chloride) is often placed on roads in winter to melt accumulated ice. The salt works by lowering the freezing point of water, causing the ice to melt, but the chloride ions formed when the salt reacts with water corrode the road surface. Some highway departments in the US and Canada have reportedly begun applying a mixture of rock salt brine and beat juice (de-sugared beet molasses) to ice-covered road surfaces instead. The mixture reportedly lowers the freezing temperature of water, and reduces corrosiveness.

• Rock salt, beet juice, conductivity tester
• Rock salt (hardware stores, supermarkets), beet juice (supermarkets, Internet), conductivity tester (science teaching suppliers); paper cups (Walmart-type store), refrigerator with freezer
• Yes, but the conductivity tester may have to be purchased on the Internet. An alternate is to construct one using one of the methods described on the Internet (see Bibliography).
1. Read about the use of rock salt for de-icing roads and the problem of corrosion, then formulate a hypothesis about how a combination of rock salt and beet juice might or might not be superior to rock salt alone.
2. Place equal amounts of water (about 2 oz.) in three 8-oz. paper cups, then place the cups in a freezer until the water turns to ice.
3. Cover the ice in the first cup with a tablespoon of rock salt.
4. Cover the ice in the second cup with a tablespoon of beet juice.
5. Cover the ice in the third cup with a mixture of one tablespoon of rock salt and one tablespoon of beet juice.
6. Measure the time for the ice in each of the cups to melt. Record your observations.
7. Now check corrosiveness. Chloride ions from the dissociated salt contribute to the conductivity of the solution. Evaluate the chloride concentration in each of the solutions by measuring the relative ability of each solution to conduct electricity using a conductivity metre.
8. Evaluate your initial hypothesis about using the usefulness of rock salt and beet juice in melting ice and preventing corrosion. If necessary, revise your hypothesis and propose additional tests.
 Time to melt ice Electrical conductivity Rock salt Beet juice Rock salt and beet juice

Terms:Deicing; Salt (sodium chloride); Freezing;Ions; Corrosion

References:

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