Key concepts
Physics
Chemistry
Density
Liquids
Introduction
You probably know that when solid objects are placed in liquid, they can sink or float. But did you know that liquids can also sink or float? In fact, it is possible to stack different layers of liquids on top of one another. The key is that all the different layers must have different densities. You can stack them by picking several liquids with a range of densities or by varying the density of one liquid by adding chemicals such as sugar or salt to it. If you choose colored liquids or add food coloring to each layer, you can even create a whole rainbow of colors in one single glass! Want to see for yourself? In this science activity you will stack several liquids—one by one—and create a colorful density column!
Background
Whether an object sinks or floats depends on its density compared with the density of the liquid into which it is dropped. All types of matter—solids as well as liquids—are made up of many different atoms. Depending on the mass of these atoms, their size and the way they are arranged, different substances will have different densities. The density is characteristic for each individual compound and defined as the mass of a compound divided by its volume. In other words, the more matter there is in a certain amount of volume, the denser a substance is. One cubic centimeter of rock, for example, is much heavier than a cubic centimeter of wood. This is because there is much more matter in the same volume of rock compared with the wood.
ADVERTISEMENT
Liquids can also have different densities. Freshwater, for example, has a density of about one gram per cubic centimeter at room temperature. Any compound—liquid or solid—that has a higher density than water will sink whereas substances with a lower density than that will float. You can test that for yourself by gathering several liquids that you have in your kitchen such as vegetable oil, corn syrup, dishwashing soap, water, rubbing alcohol and more. Which one of these do you think will sink or float in water? Find out in this activity!
Materials
Glass or cup
Water
Food coloring
Scissors
Rubber band (wide)
Small piece of wax
Popsicle stick
At least two small, clear jars or transparent mini cups (two ounces) with lids
Permanent marker
Masking tape
Three tablespoons
Dark corn syrup
Vegetable oil
Penny
Paper towels
Rubbing alcohol, dishwashing soap and other liquids (optional)
Sugar (optional)
Preparation
Gather all your materials at a workspace that can tolerate spills of all the liquids.
Fill a cup with tap water and add a couple of drops of food coloring to the water.
Ask an adult to help you cut and prepare small pieces (about 0.5 by 0.5 centimeter) of the rubber band, the popsicle stick and the wax.
Place the two empty jars in front of you (without the lids) and label them “1” and “2” with a piece of tape and the permanent marker.
Procedure
Take a clean tablespoon and pour two tablespoons of corn syrup in jar 1.
With the second tablespoon, carefully pour two tablespoons of colored water into jar 1 on top of the corn syrup. What happens to the water on top of the corn syrup? Does it mix or stay separate?
Use the third clean tablespoon to pour two tablespoons of vegetable oil in jar “1” on top of the colored water. Do you see mixing of the liquids? What happens to the oil? Does it float on top or sink to the bottom?
Now take empty jar 2 and add the same liquids—but in reverse order. Start by pouring in two tablespoons of vegetable oil.
