Colloids
To introduce colloidal solutions and familiarise students with filtering techniques.
The science behind this experiment
In the previous experiments the solutes were dispersed as molecules or ions throughout the solvent. It can happen that the solute does not dissolve completely but its molecules remain aggregated as small clusters; these solutions are called colloids and have different properties from true solutions.
Under certain conditions, it is possible to obtain colloids from a wide range of substances, such as metals, oxides and sulphides.
Some colloids, such as soaps, form micellar solutions where the solute exists as particles called micelles.
Equipment used
- Test tubes — PLA-007
- Test tube rack — PLA-012
- Test tube holder — PLA-017
- Spatula — PLA-024
- Iron stand — CHE-037
- Universal clamp — HEA-010
- Right angle clamp — PLA-016
- Glass funnel — PLA-002
- Filter paper — CHE-035
Chemicals and reagents
- Sulphur — R:11-16 S:41
- Ethanol — R:11 S:7-16
Questions for students
- Describe the solution. What was it like before and after the addition of water?
- What happens to the solution after filtration? Why?
What to expect
The sulphur dissolves in ethanol to give a clear, pale yellow solution. After adding water, the colloidal solution looks like a milky white solution. The same results are obtained with milk that forms micelles with water molecules. Filtration does not affect the solution because the sulphur particles are much smaller than the pores in the paper.
Disposal
Dispose of liquids into the liquid wastes container.
Run this experiment in your classroom
This experiment is part of ATP Volta — a self-contained mobile science lab that turns an ordinary classroom into a working STEM laboratory, with over 200 experiments in physics, chemistry, biology, robotics and engineering. Gali, the AI tutor built into ATP Connect, guides students through each step and answers their questions at the bench.
See the ATP Volta mobile science labTalk to our team