SCIENCE with Ms Lun
Swimming raisins
Objective
Difficulty:
Time: 10-15 mins
Adult supervision: minimal
Dangers: none
To show how the density affects the buoyancy of an object
Materials
2 clear drinking glasses
water
soda (soft drink) i.e. lemonade
baking soda
vinegar
raisins (about 6)
Instructions
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Half fill the first glass with tap water.
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Fill the second glass with soda.
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Add 3 raisins to each glass. Did they sink or swim?
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The raisins in the water should've sunk to the bottom. Now add the baking soda and stir gently. What happens to the raisins now?
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Top up the glass with vinegar and see the raisins rise
The raisins stay at the bottom when baking soda is added
But look at them swim when vinegar is added
And here's what happened in the soda
The Science
Density: a measure of how much mass there is in a given solution. The density of a liquid also determines whether something will float or sink. Raisins are more dense than water and will sink. However, you will notice that raisins rough not smooth. When air bubbles get trapped in the grooves and ridges of the raisins, it causes them to rise.
Soda contains carbon dioxide. The gas starts to come out of the soda when the lid is taken off the soda bottle and gets trapped on the raisin. As the raisin rises to the surface, some of the bubbles are released and the raisin sinks. It collects more bubbles as it sinks making the raisin rise again. As the soda goes flat, no more bubbles form and the raisins sink.
The vinegar and soda reaction (acid plus alkali) also produces carbon dioxide.
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