Cleaning chemistry: soaps and detergents

In this collection of activities, students develop their understanding of key chemical ideas relating to soaps and detergents. Suitable for 11–16 year olds, the resources draw on a variety of scientific, historical and everyday contexts, with activities ranging from making and testing soap to product analysis. Stimulate and engage your students to learn about:

• The chemical composition of cleaning products
• How soaps and detergents work
• Saponification, soap ‘scum’ and soapless detergents
• The history of soap
• Experimental design and planning investigations

Each activity includes instructions for students, as well as editable worksheets and resources available for download.

1. Testing shower gels and soaps

Summary

Students conduct a practical experiment using samples of 5–6 shower gels and soaps, determining their pH values and testing their effects on cooking oil. After recording their observations, students answer a series of short questions to help them interpret their results and explore what further tests could be done to identify the ‘best’ cleaning product.

The extension activity gives students the opportunity to build on their work in ‘Testing shower gels and soaps’ by planning their own investigation to compare the properties of soap and detergent products. (It may be helpful to use the demonstrations in ‘How do soaps and detergents work?’ (below) as guidance.)

An additional handout, ‘Did you know about shower gels and soaps?’, provides further information about the ingredients and composition of these products.

2. Look at the label!

Summary

Students choose three shower gels or soap bars to research and analyse. Using information from the ‘Cosmetic ingredients database’ handout, students look up key ingredients in each product and identify what they do (eg surfactants, emulsifiers and so on). For each product, they also record its price and any claims made about it by the brand or manufacturer. When they have completed their research, students answer a series of questions to help them compare the different products and reflect on how they are used.

Note

The ‘Cosmetic ingredients database’ handout is only available for download using the links in the box below. It will not be included with the ‘Download all’ option at the bottom of this page.

3. Making soap

Summary

Students conduct a practical experiment to make their own soap using cooking fat, water and sodium hydroxide. They then work through a short series of questions to explore the process involved and draw out key points about the chemical reaction that takes place.

An additional handout, ‘Did you know about detergents?’, provides further information about saponification, soap ‘scum’ and soapless detergents. The handout also features questions to check and reinforce students’ understanding of what they have read.

4. The history of soap

Summary

Students read a short text about the history of soap and soapmaking, before answering questions to check and develop their understanding of what they have read. They explore why soap only started to be used for washing people after 1853, and how soaps were advertised in the past.

5. Using soap and soapless detergents

Summary

In this group activity, students read a range of people’s views about using soaps and detergents. After discussing the different ideas expressed with their group, students work together to put the views in rank order according to how far they agree with each one. They then discuss their ranking and the reasons behind it with the class.

6. Forever blowing bubbles

Summary

Students apply their knowledge about soaps and detergents to design an experiment investigating the effect of different types of soap on bubbles, with the objective of answering the following questions:

• Why do the bubbles made by bubble bath disappear when you then use ordinary soap?
• Does this depend on the type of soap, the type of bubble bath, or both?

Additional resources

This key words handout provides further information about important terms relating to the chemistry of soaps and detergents.