How does salt affect ice?

Author: Maddie Van Beek

It's almost December and the weather will be getting colder! In Fargo, the roads and sidewalks can get pretty icy, so people take extra care with driving and walking in the winter. ​Have you ever seen salt on the sidewalks in the wintertime? Most of you probably know that salt causes ice to melt. People sprinkle salt on icy sidewalks to make them less slippery. Have you ever wondered how that works? That’s what we are going to find out today!

Sodium Chloride, otherwise known as common table salt.

This is a single grain of table salt under a microscope!

This machine is called a gritter. This is a gritter about to spread salt on the roads in Germany.

Why does salt melt ice?

When you dissolve salt in water, the water is harder to freeze. Usually, water freezes at 32 degrees Fahrenheit (0 degrees Celsius). When you add salt to water, it has to be colder than 32 degrees Fahrenheit in order to freeze. Thus, adding salt to water lowers the freezing temperature.
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Watch this video to find out more about the science behind why salt melts ice: 
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Check out this link for more information: 
http://science.howstuffworks.com/nature/climate-weather/atmospheric/road-salt.htm
 
Now that you know why salt melts ice, let’s test it out!
 
YOU WILL NEED:

• Clear glass
• Water
• Ice cubes
• String

 
Here’s what to do!

1. Fill your glass about ¾ full with water.
2. Add about 5 ice cubes.
3. Cut a piece of string about 1 foot long.
4. Dangle the string into the water and try to catch an ice cube. When you lift the string out, do any ice cubes stick to it?
5. Let’s try it again. Dangle the string into the water over the ice cubes. This time, sprinkle some salt over the ice cubes. Wait a few seconds, then lift the string up. Do any ice cubes stick this time? Yes! Why did the salt make the difference? Remember, salt causes ice to melt! When you sprinkled salt on the ice cubes, they began to melt, but the water around it quickly refroze. The refreezing trapped the string onto the surface of the ice cubes. See how many ice cubes you can catch at once!
6. Does more salt change the effect? Try it out!

 
Now that you know how salt affects ice, use this same science to make your own slushy without the aid of a freezer!
​
YOU WILL NEED:

• Fruit juice
• Ice cubes
• 1 Gallon Ziploc bag
• 1 smaller Ziploc bag
• Salt

 
Here’s what to do!

1. Carefully pour fruit juice into the smaller bag and seal it shut.
2. Put ice cubes into the gallon-sized bag and add the salt.
3. Place the sealed smaller bag inside the gallon-sized bag.
4. Seal the larger Ziploc bag shut.
5. Shake it up!!!
6. Remember, salt lowers the freezing temperature of ice, so it causes the ice to melt. As the ice melts, the salty mixture also becomes colder… just cold enough to freeze up your fruit juice!
7. Once your fruit juice reaches the desired slushy consistency, place the bag in the sink, remove the smaller bag from the larger one and rinse it off with cold water.
8. Open your fruit juice bag and enjoy your homemade slushy!

 
References
http://www.sciencekiddo.com/salt-melts-ice-experiment/
http://www.sciencekiddo.com/fruity-ice-slush/
https://www.highlightskids.com/science-questions/how-does-salt-melt-ice-and-snow
http://science.howstuffworks.com/nature/climate-weather/atmospheric/road-salt.htm
​https://en.wikipedia.org/wiki/Salt

Image and video credits, in order of appearance:

Soric, D., 2009. Salt shaker on a white background. Image uploaded from Wikimedia Commons on 11/27/2016. https://upload.wikimedia.org/wikipedia/commons/thumb/7/78/Salt_shaker_on_white_background.jpg/800px-Salt_shaker_on_white_background.jpg File used in accordance with the 
Creative Commons Attribution 2.0 Generic Image was not changed. 

Chhe, 2009. SEM image of a grain of table salt. Image uploaded from Wikimedia Commons on 11/27/2016. https://upload.wikimedia.org/wikipedia/en/thumb/9/9b/Single_grain_of_table_salt_%28electron_micrograph%29.jpg/800px-Single_grain_of_table_salt_%28electron_micrograph%29.jpg File in the Public Domain. 

Heidas, 2005. Schneepflug strasse hinten. Image uploaded from Wikimedia Commons on 11/27/2016.
https://en.wikipedia.org/wiki/Winter_service_vehicle#/media/File:Schneepflug_Strasse_hinten.jpg File used in accordance with the CC Attribution-Share Alike 3.0 Unported. Image was not changed

Reactions, 2015. How does salt melt ice? Video uploaded from YouTube on 11/27/2016. https://youtu.be/JkhWV2uaHaA