• Skip to primary navigation
  • Skip to main content
  • Skip to footer
Zippy Facts Logo

Zippy Facts

Interesting Random Facts

  • Animals
  • Culture
  • Firsts
  • Food
  • Geography
  • Health
  • History
  • Inventions
  • Language
  • Mythology
  • Odds
  • People
  • Religion
  • Science
  • Space
  • Universe
  • World
You are here: Home / Science / Why does Adding Salt to Ice and Water Make it So Much Colder Than the Freezing Point?

Why does Adding Salt to Ice and Water Make it So Much Colder Than the Freezing Point?

March 26, 2020 by Karen Hill

The normal temperature of an ice and water slush is 32 degrees Fahrenheit (0 degrees Celsius).

But that’s not cold enough to freeze ice cream. It has to be at 27 degrees Fahrenheit (-3 degrees Celsius) or below. Salt is what does the job. Lots of other chemicals would do the trick, but salt is cheap.

When ice and salt are mixed, some salt water is formed and the ice spontaneously dissolves in the salt water, making more salt water. That’s what happens when you throw salt on an icy sidewalk or driveway; solid ice plus solid salt becomes liquid salt-water.

Inside a piece of ice, the water molecules are fixed in a definite, rigid geometric arrangement. This rigid arrangement breaks down under the attack of the salt, and the water molecules are then free to move around loosely in the form of a liquid. But it takes energy to tear down the solid structure of ice molecules, just as it takes energy to tear down a building.

For a piece of ice that is in contact with nothing but salt and water, that energy can come from nowhere but the heat content of the salt water. So as the ice breaks down and dissolves, it borrows heat from the water, lowering its temperature. The slush gets repaid by taking heat out of the ice-cream mixture, which is, of course, just what you want it to do.

Put equal amounts of cracked ice in two identical glasses. Pour just enough water into each one to make the ice begin to float. Then dump a lot of salt into one of the glasses and poke it down into the ice a bit. After several minutes, check the temperatures with a kitchen meat thermometer. (Lord knows why, but many of them do go down below freezing.)

You’ll find that the salted ice gets much colder than the plain ice. You may even be able to scrape some frost off the outside of the salted glass with your fingernail.

Related Facts

  • Why does the freezing point of water change with pressure and why doesn't deep sea water freeze?
  • Why does Adding Salt to Boiling Water Make it Hotter?
  • What is the Difference Between the Freezing Point and Melting Point of a Substance?
  • How does adding salt to the water before boiling eggs prevent the eggshells from cracking?
  • What is a Salt Pig and How does a Salt Pig Keep Salt Dry?
  • Why Is Glacier Ice Purer Than Regular Ice and How Is Glacier Ice Formed Without Impurities?
  • How Do You Change the Freezing Point of Fresh Water?
  • Why does Water Boil and Can Water Get Hotter Than the Boiling Point?
  • Why Is It Colder At the Poles Than At the Equator and Why Is It Warmer At the Equator Than At the Poles?
  • Why does Water From the Shower Get Colder after Adjusting the Hot and Cold Water Mix?
  • Why Is Kosher Salt Better Than Regular Table Salt?
  • Why Is Freshly Ground Salt Better Than Granulated Salt?

Filed Under: Science

About Karen Hill

Karen Hill is a freelance writer, editor, and columnist. Born in New York, her work has appeared in the Examiner, Yahoo News, Buzzfeed, among others.

Previous Post: « Why does a Silver Spoon Used to Stir Coffee Get So Hot?
Next Post: Why does Water From the Shower Get Colder after Adjusting the Hot and Cold Water Mix? »

Footer

Follow

  • Facebook
  • Flickr
  • GitHub
  • Google+
  • Instagram
  • LinkedIn
  • Medium
  • Pinterest
  • StumbleUpon
  • Tumblr
  • Twitter
  • YouTube

Categories

Accomplishments Animals Culture Firsts Food Geography Health History Inventions Language Mythology Odds People Religion Science Space Universe World Your Body

About

Zippy Facts empowers the world by serving educational content that is accessible to everyone.

A tribute to growing up, zippyfacts.com showcases interesting and unusual facts about the world.

Our mission is to use technology to facilitate knowledge transfer and sharing.

Copyright © 2021 Zippy Facts

  • About Us
  • Contact
  • Privacy Policy