Allow about 1 dm 3 for each working group in the class.

Hard water – A supply of hard water can be made by stirring solid calcium sulfate into a large volume of tap water, allowing to stand for some time then, after the undissolved solid has settled out, decanting the clear solution into a container suitable for students to collect their samples as required.

To obtain soap solution from soap flakes – dissolve soap flakes (or shavings from a bar of soap) in ethanol – use IDA (Industrial Denatured Alcohol) (HIGHTLY FLAMMABLE, HARMFUL) – see CLEAPSS Hazcard HC040a and CLEAPSS Recipe Book RB000. They do not form a stable emulsion and precipitate out overnight. Note that most liquid hand washes are based on the same detergents as washing-up liquids and do not contain soap. Lux soap flakes are ideal for making liquid soap if you can source them. Granny’s Original and other non-branded soap flakes work fine but need to be used in solution as soon as they are made.

Liquid soap - Genuine liquid soap or soap flakes from which the liquid can be made, is increasingly difficult to obtain. Wanklyn’s and Clarke’s soap solutions should still be available from chemical suppliers.

Liquid detergent – Any washing-up liquid or multipurpose detergent will suffice.

Lycopodium powder is a potential allergen.

Other powders – Any powders used other than talcum powder, such as lycopodium powder or carbon powder, should be subject to a risk assessment.

Read our standard health and safety guidance.

Access to a supply of purified water (distilled or deionised), about 1 dm 3 per working group.

Talcum powder, in pepper pot or similar dispenser.

The sewing needle should be a fine needle, and for safety issued to students with the pointed end inserted into a piece of card bearing a safety warning about handling the needle.

If a full range of experiments is desired, the time taken could amount to 30 minutes, but this may not be justified in terms of the learning objectives concerned. Each experiment should take no more than two minutes, though the cleaning of the beaker between experiments may take up more time than expected. This is a series of quick, simple, class experiments which can be extended or shortened as desired. Finally the same experiments can be repeated using samples of hard water to compare the effects. A needle can be carefully floated on a clean water surface and the effect of adding detergent or soap observed. This can be repeated with other powders after cleaning the beaker and using fresh water samples.

Hamied Inspirational Chemistry ProgrammeĪ fine insoluble powder, such as talcum powder, is sprinkled on a clean water surface in a beaker, a drop of detergent or soap solution added to the centre, and the effect observed as the surface tension of the water is changed.

Introductory maths for higher education.

The physics of restoration and conservation.

Surface tension half life