Why is an iceberg frozen but not the water below it | Fizzics Education

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# Why is an Iceberg Frozen but not the water below?

### You will need:

• Two balloons
• Salt, funnel and a measuring spoon
• 75mL of water per balloon
• A freezer
• A stopwatch

1

Place a funnel into the mouth of the balloon and add at least 1 tablespoon of salt into the
balloon.

2

Carefully measure 75mL of water pour it into the balloon, tie the balloon and shake to dissolve the salt.

Using the funnel, add 75mL of water to the other balloon and tie it.

3

Place both balloons in the freezer and start the timer.

4

Check the balloons on 10-minute intervals. Which freezes first – salt water or fresh water?

5

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### Why Does This Happen?

Adding salt to water lowers its freezing point below 0o Celsius. As ice forms in polar regions, the salt within the forming ice is ejected into the surrounding water. This causes water below the ice to exist at sub-zero temperatures.

Also, water expands when it freezes – try measuring the diameter of the balloon with vernier callipers before freezing and afterwards once it has frozen > better than exploding cans in the freezer! Expanding causes the ice to be less dense than the surrounding liquid water, thereby the ice floats.

People use salt to melt ice on roads, an important safety concern for motorists.

### Variables to test

More on variables here

• Does vegetable oil do the same thing?