Making Rock Candy.

With supersaturated solutions

A solution is a mixture of a solute and a solvent. A solute is a substance that is dissolved in another substance, known as a solvent. Take the example of a sugar solution. It is made from sugar, the solute and water, the solvent.

We can use hot water to dissolve more solute than at normal temperature. As we saw previously when water is heated, its capacity to dissolve an amount of solute, be it salt or sugar, increases dramatically.

When a given volume of water has dissolved as much solute as it can at a particular temperature we say a saturated solution is formed. By heating the volume of water we can dissolve even more solute. As this hot water begins to cool back to room temperature it contains much more solute then it can cope with at room temperature. We say the solution is now supersaturated. In a supersaturated solution the solute particles try to find a way to come out of solution. Crystallization occurs rapidly if a small seed crystal is placed in the solution.

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We make supersaturated solutions when we make confectionery such as rock candy.

View the video on the right.

1) What is a supersaturated solution?
2) How is a supersaturated solution formed?
3) Identify the solute and the solvent in the process of making rock candy.
4) Why do sugar crystals form in the supersaturated solution as it cools?
5) Why is a stick covered in sugar placed in the supersaturated solution?
6) What is the difference between a supersaturated solution and a saturated solution?

NOTE - You must be supervised by an adult at all times when making rock candy. Since the sugar solution can be very hot you need to wear the appropriate protective gear as specified in the video.

Sourced from https://www.youtube.com/watch?v=VpOU0Fo7QfU&t=42s at 8.05 14/07/20