In this activity, you learn about a concept called density. Density is really important as it allows us to say whether something will float or sink.
For example: Helium has a lower density than air so if you fill a balloon with helium it will float! Ice has a lower density than water so it floats.
Liquids can have different densities too. Water is more dense than oil, so oil will float on top of water.
Image by Annalise Batista from Pixabay
Experiment
You can download the experiment here.
What do you think a unicorn might drink? Something sweet? Something colourful?
Why don’t we see if we can make a drink for some unicorns?
You will need:
Sugar
Food colouring
3 cups
Tall container such as a tall glass
Funnel/pipette/plastic syringe (not essential but makes things a little easier)
YOU WILL NEED HELP FROM AN ADULT
Ask a grown up to boil some water.
Put 6 tablespoons of water into each cup.
Into the cups add the following
Cup 1: No sugar and two drops of red food colouring
Cup 2: 2 Tablespoons of sugar and two drops of green food colouring
Cup 3: 4 Tablespoons of sugar and two drops of blue food colouring
Stir each mixture until the sugar disappears (this is called dissolving and the clear liquid that we make is called a solution)
Cup
1
2
3
Tablespoons of sugar
0
2
4
Food Colouring
Green
Red
Blue
During science we make a guess at what we think will happen, this guess has a fancy word, called a hypothesis. What do you think will happen if we carefully mix these solutions?
Method
Pour the blue solution into the bottom of the container.
Carefully pour the red solution down the side of the container (use a funnel/pipette/plastic syringe if you have one, it makes this easier.)
You should see that the colours will stay separated.
Repeat the above step with the green solution.
Dr Amanda Pearce has tried this experiment at home. Check out her video and see how hers went. If you want to send us pictures of your Unicorn Drink tweet us @ChemBAMEditor
Questions
What happened to the solutions?
Why do you think this happened?
What is different about the three solutions?
Explaining our results
These solutions all have different densities. Density can be thought of as the amount of weight for every millilitre (ml) of volume. (If we had weighed the mixtures before mixing them they would have weighed different amounts).
All of the solutions are 6 tablespoons in volume. The ONLY difference is the amount of sugar.
The blue solution has the most sugar in it. This means it has a high density. That’s why it stays at the bottom.
The red solution has no sugar in it, so it has the lowest density (it’s the lightest). That’s why it stays at the top.
The green solution has a little bit of sugar in it. It is lighter than the blue solution, but it is heavier (more dense) than the red solution. That’s why it stays in the middle.
Going further
Try this with a small glass using water, oil and honey.
Can you put these in order of density?
Researcher perspective
Chemists use mixtures of liquids regularly. One thing we use this for in a research lab is separation.
One liquid can be used to extract a chemical you have made from another liquid. You might be trying to make a new drug molecule in a solvent (liquid) in the laboratory. But there will be other chemicals (we call them byproducts) in the solvent too. If you add another liquid, you can get your product (the drug molecule) to move into the new liquid. You can let the two liquids separate and pour off the liquid with all the chemicals you don’t want, leaving you with the one you do!
Curriculum
Y1/Y2 working scientifically
Pupils should be taught to use practical scientific methods, processes and skills including:
asking simple questions and recognising that they can be answered in different ways
observing closely, using simple equipment
performing simple tests
identifying and classifying
using their observations and ideas to suggest answers to questions
KS3
similarities and differences, including density differences, between solids, liquids and gases
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