Have you ever slipped on an icy surface or seen a video of someone slipping on ice? Have you ever been in a car that has slipped on an icy road? To keep this from happening, salt is sometimes put down on icy roads and sidewalks to help the ice melt faster, even if it’s still cold outside. In this experiment, you will explore how to lower the melting point of ice to make it melt quicker.
Created by Madness Stock from Noun Project
Student Guide
Getting Salty
Experimenting with melting points
When different substances (table salt, rock salt, and sugar) are added to ice, which one will lower the melting point of the ice the most?
This resource was originally published in PhysicsQuest 2019: Heat.
When different substances (table salt, rock salt, and sugar) are added to ice, which one will lower the melting point of the ice the most?
- Table salt
- Rock salt
- Sugar
- Cups for making ice (7)
- Stopwatch
- Freezer
Intro
Before the experiment
How do you think the substances (table salt, rock salt, and sugar) will change the melting point of the ice?
Predict the order in which ice containing each of these substances will melt from fastest to slowest.
- _______________________ (melts fastest)
- _______________________
- _______________________ (melts slowest)
Setting up
Fill the smaller cups with the substances as follows and label as follows:
- Cup 1 – 1/3 of the total table salt
- Cup 2 – 2/3 of the total table salt
- Cup 3 – 1/3 of the total rock salt
- Cup 4 – 2/3 of the total rock salt
- Cup 5 – 3 packets of sugar
- Cup 6 – 6 packets of sugar
Label Cup 7 – water only (this cup will be your baseline)
Carefully pour 8 oz. (one cup) of water into each cup for the substances to dissolve. Make sure each cup is filled to the same level.
Place all seven cups in the freezer for at least two hours, or until the water has frozen.
Make a chart for recording the time it will take each cup of ice to melt.
During the experiment
Collecting data
Remove the ice cups from the freezer.
Place the cups somewhere warm—the warmer, the better.
Start the stopwatch to keep track of how long it takes each cup of ice to melt.
Record how much time it takes for each cup of ice to melt completely.
Analyzing data
How did the order of the ice melting compare to your predictions? Which cup of ice melted first?
Compare the time it took for ice made with just water to melt compared to the other cups. Did it melt faster or slower?
Did ice made from water mixed with different amounts of the same substance melt at the same time? Why or why not?
List the substances from the least effective to most effective at lowering the melting point of ice.
- _______________________ (least effective)
- _______________________
- _______________________ (most effective)
Conclusion
Now that you have determined which substance works the best at lowering the melting temperature of the ice, how would you explain to a school that they should use it on icy sidewalks to keep people safe?