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Homemade Iceberg Experiment

Find Out Why Sea Ice is Fresh Water

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Iceberg west of Ilulissat inlet, Greenland

Icebergs form from glaciers, so they are freshwater, but even if they float in seawater, they freeze freshwater ice, not saltwater.

Uta Wollf, Rodebay
Did you know icebergs consist primarily of fresh water? Icebergs primarily form when parts of glaciers break off or "calve" icebergs. Since glaciers are made from snow, the resulting icebergs are freshwater. What about ice that forms in the ocean? This sea ice often breaks into ice floes when a solid sheet of ice shifts and thaws in the spring. Although the sea ice comes from seawater, it is fresh water, too. In fact, this is one method of desalination or removing salt from water. You can demonstrate this for yourself:

Iceberg Experiment

You can make your own homemade "seawater" and freeze it to make sea ice.
  1. Mix up a batch of synthetic seawater. You can approximate seawater by mixing 5 grams of salt in 100 ml of water. Don't worry too much about the concentration. You just need salty water.

  2. Put the water in your freezer. Allow it to partially freeze.

  3. Remove the ice and rinse it in very cold water (so you don't melt too much of it). Taste the ice.

  4. How does the ice cube taste compared with the salty water left in the container?

How It Works

When you freeze ice out of saltwater or seawater, you're essentially forming a water crystal. The crystal lattice doesn't make much room for salts, so you get ice that is more pure than the original water. Similarly, icebergs that form in the ocean (which are really ice floes) aren't as salty as the original water. Icebergs that float in the sea don't become contaminated with salt for much the same reason. Either the ice melts into the ocean or else relatively pure water freezes out of the seawater.

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