Al wonders if adding salt to water will affect how long it takes the water to freeze. Al thinks that salt water will freeze more quickly than fresh water.
He decides to check his hypothesis by conducting an experiment. Al takes
two ice trays and fills one with distilled water and the other with distilled
water that has two tablespoons of salt added. He makes sure he puts
exactly the same amount of water in each ice tray. Al takes the trays and
puts them side by side in the freezer. Al checks the ice trays every 10
minutes to see if the water in each tray has begun to freeze. Al finds that
after 20 minutes the water in the ice tray without the salt has started to
form ice, while the ice tray with the salt water is still completely liquid.
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The hypothesis is that salt water freezes faster than fresh water.

The dependent variable is time taken for ice to appear.

The independent variable is presence or absence of salt

The constants are the amount of water in each tray, freezing conditions and length of time of exposure to freezing condition.

The control group is the tray to which salt was not added

The experimental group is the tray to which salt was added

The presence of solutes in a solution causes the freezing point depression.

A solution is made up of a solute and a solvent. In the presence of a solute, the freezing point of a pure solvent is decreased. This is because freezing point is a colligative property.

Colligative properties depend on the amount of solute present.

Hence, the pure water freezes faster (ice begin to appear earlier) than the salt water.

The hypothesis put forward in this experiment was found to be invalid by the experiment.

For more about colligative properties, see

it is stable as it is in group 0 which have full outer shells of electrons

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