Estimated Time: 20 minutes
Background
In many foods—like salad dressings, and mayonnaise—oil and water need to mix to give a smooth, creamy texture. But oil and water don’t naturally mix. They separate because they are different kinds of molecules. To keep them together, food scientists use emulsifiers—special ingredients that help oil and water mix and stay mixed.
Egg yolk is a natural emulsifier commonly used in foods like mayonnaise. Even though mayonnaise contains a large amount of oil, the egg yolk helps create a smooth, creamy texture by keeping the oil and water mixed. In this experiment, we’ll use soap as a substitute for egg yolk. Like egg yolk, soap has emulsifying properties that can temporarily help oil and water blend together.
Download the Lab and Worksheet – Available free of cost for a limited time. See our Free Resources Policy.
Materials (per group)
- Cooking oil
- Tap water
- Liquid dish soap
- Four clear plastic cups
- Plastic spoon
- Measuring cup
- Tablespoon
- Timer or clock
- Marker (for labelling)
- Lab worksheet
Procedure
- Label your four cups or jars as A, B, C, and D.
- To each cup, add:
- 1 cup of water
- 1/2 tablespoon of oil
- Add dish soap as follows:
- Cup A: No soap
- Cup B: 1 drop
- Cup C: 2 drops
- Cup D: 3 drops
- To add a drop of soap:
- Gently tilt the dish soap bottle until a small drop forms at the tip of the opening.
- Let the drop fall naturally into the cup.
- Do not squeeze the bottle, as this may release too much soap at once.
- If needed, tap the bottle gently or use the cap to control the drip, depending on the bottle design.
- Stir each mixture with a plastic spoon for 15 seconds.
- Let the mixtures sit undisturbed for 5 minutes.
- Observe and compare how much oil has separated in each cup.
- Record your observations and any patterns you notice on the lab worksheet.
Download the Lab and Worksheet – Available free of cost for a limited time. See our Free Resources Policy.
Observation Table
| Cup | Amount of Soap | Initial Appearance (after mixing) | After 5 Minutes |
| A | None | ||
| B | 1 drop | ||
| C | 2 drops | ||
| D | 3 drops |
Lab Questions
- Which cup had the best mixture after 5 minutes?
- How did adding more soap affect the mixture?
- What do you think the soap is doing to help oil and water mix?
- In real foods, eggs are often used as emulsifiers. How might this experiment help you understand the role of egg yolks in mayonnaise?
