Ice balloons and salt

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Ice balloons and salt
Age Range all ages
Group Size small (1-5), medium (6-20)
Setting indoors
Setup Time very long (1 day+)
Duration medium (11-30 min), long (31 min - 1 hr)
Subjects states of matter, water
Key terms freezing point, melting point
Materials balloons, water, salt, popsicle sticks, trays, sugar, food coloring, nails
Alias salt ice balloons
Presentation Style active, interactive, student led

Brief Description

Students will pour salt and food color on frozen blocks of ice. Ice changes the freezing point of water and the ice will melt.

Scientific Background

Salt lowers the freezing/melting point of water. Water freezes when theĀ­ temperature of water reaches 32 degrees Fahrenheit (0 degrees Celsius). When you add salt, that temperature drops: A 10-percent salt solution freezes at 20 F (-6 C), and a 20-percent solution freezes at 2 F (-16 C). On a roadway, this means that if you sprinkle salt on the ice, you can melt it. The salt dissolves into the liquid water in the ice and lowers its freezing point.

If you ever watch salt melting ice, you can see the dissolving process happen -- the ice immediately around the grain of salt melts, and the melting spreads out from that point. If the temperature of the roadway is lower than 15 F or so, then the salt really won't have any effect -- the solid salt cannot get into the structure of the solid water to start the dissolving process. In that case, spreading sand over the top of the ice to provide traction is a better option.

This Is How You Play

  1. Fill balloons with water and place in the freezer until frozen completely.
  2. When it's time for the activity, remove the balloon from the ice block and place on a tray to catch the melting ice.
  3. Students will get to experiment with the ice by pouring salt, sugar and some food coloring.
  4. You can optionally give students digging tools like popsicle sticks or blunt nails.


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