When both are liquids
Emulsions.
Milk and butter
Milk and butter are both colloids made from oil and water. In milk, tiny oil droplets are spread through water. Butter is different.
What might butter be?
What this lesson covers
The idea
Colloids in which both the dispersed phase and the dispersion medium are liquids are emulsions; oil-and-water emulsions are oil-in-water or water-in-oil depending on which is dispersed, and emulsifying agents stabilise them.
Milk and butter
Milk and butter are both colloids made from oil and water. In milk, tiny oil droplets are spread through water. Butter is different.
What might butter be?
- Tiny water droplets spread through oil
- Tiny oil droplets spread through water, like milk
- Oil and water in two separate layers
Make an emulsion and wait
Choose which liquid forms the droplets. Let time pass with, and without, an emulsifying agent.
Emulsions
Emulsions are colloids in which both the dispersed phase and the dispersion medium are liquids. With oil and water they are oil-in-water or water-in-oil, depending on which one forms the droplets. Emulsifying agents stabilise emulsions.
Oil-in-water: milk, vanishing creams. Water-in-oil: butter, body lotions, cold cream. Proteins in milk and butter act as emulsifying agents.
Some medicines are made as emulsions, so they disperse in water, taste better and feel less greasy.
Notes
An emulsion is a colloid of two liquids: oil-in-water (milk) or water-in-oil (butter). Emulsifying agents stabilise it.
Check yourself
Milk is an oil-in-water emulsion. Which liquid forms the droplets?
Which of these is a water-in-oil emulsion?
An emulsion is a colloid in which…
What do emulsifying agents do?
- Oil — correct. Yes. Oil is the dispersed phase.
- Water. Water is the dispersion medium.
- Neither. An emulsion has droplets of one liquid in another.
- Milk. Milk is an oil-in-water emulsion.
- Vanishing cream. Vanishing cream is an oil-in-water emulsion.
- Butter — correct. Yes.
- both the dispersed phase and the dispersion medium are liquids — correct. Yes.
- a solid is spread through a liquid. That is a sol, not an emulsion.
- a gas is spread through a liquid. An emulsion has two liquids.
- Make the droplets settle. They keep droplets dispersed.
- Stabilise the emulsion — correct. Yes. For example, proteins in milk and butter.
- Turn the emulsion into a solution. The mixture stays a colloid.