Soap Challenge

Educational objective

To develop, as a group, the ultimate remoulded soap recipe and design and produce soap.

Soap Challenge

Download student activity sheet [pdf]

Key student learning

• The properties of soap alter when you melt it.
• Using warm water you can melt soap so that it is pliable and able to be moulded. 
• Soap will harden again after being melted and the original properties will return.
• Investigative techniques to make the best soap.

Materials needed per group

• One bar of cheap white soap (not clear soap)
• One mixing bowl or jug, of at least 500 ml capacity
• One cheese grater, preferably with several different grating plates
• Warm water from a hot tap or kettle
• Food colouring
• Mixing utensils (a variety of forks, spoons and spatulas if possible)
• Plastic tray or large plate
• Pipette
• Latex-free gloves or washing-up gloves

Optional

• Food flavouring (e.g. peppermint) or fragrance oils (e.g. rose); food flavouring is cheaper but also gives an aroma
• Glitter
• Decorative cake cases, silicone ice trays, baking trays or cookie cutters
• Decorative packaging, e.g. cellophane, cardboard, paper, ribbon

The activity

There are many ways you could choose to run this activity, but the format suggested below will spread over about two sessions.

• In groups students could work out the optimum way to complete part of the method. You could examine and discuss investigation methodology – e.g. it is important to change only one variable at a time, ensuring a fair test, recording actions and the results. Investigations could include the best base soap, best size grater, the optimum temperature for the warm water and the optimum amount of colour and fragrance to add.
• In the next session each group should test the soaps that they made and choose which they think is the best. Using all the individual group results they should compile the ultimate soap recipe.

Practicalities and safety

• Hypoallergenic facial soap is best if you have students with sensitive skin or allergies. We also tried a range of facial and bath soaps, branded soaps as well as supermarket own brands, and found no difference in performance between them. So we advise you to go for the cheapest!
• Use latex-free protective gloves to avoid staining hands with the colouring and to protect skin from prolonged exposure to soap ingredients.
• If you choose to use essential oils, seek advice from the salesperson on which are suitable for children/sensitive skin. Certain oils are also harmful to people with some medical conditions. If in doubt use food flavouring instead.
• The finished soap should be left to dry for 2–3 days in a cool dry place, after which it will be ready to use or put inside a package.
• If you want different soap bars with different colours you should separate the mixture and add the different colours at step 3 of the instructions.
• If you want different soap bars with different smells you should separate the mixture and add the different aromas at step 4.

Discussion

• What makes the best soap?
• How does soap clean skin?
• If we use coloured soap why does the colour not come out on our skin?
• When making soap what considerations do you think you have to take into account?
• What other materials behave like soap when they are heated?
• How do the properties of soap change throughout this activity?

Extensions

• You could make one really large soap bar by making the mixture with 4–5 plain white soap bars and putting the mixture into a plastic food container. Pop the large soap bar out of the container, and when it has set slice it like a cake. You could even make layers of different colours for a stripy end result.
• Visit a soap shop for inspiration.
• The activity provides a link to thinking about how people clean themselves, so you could use it together with the Bath Fizzers activity.
• Your club could use this activity as a youth enterprise project incorporating STEM and sell the soap as a product. The money made from this could also contribute to funding your science club.
• Make ‘real’ soap using caustic soda and oils. This involves a spectacular exothermic reaction and illustrates the fascinating process still used to make an everyday item, but there are significant safety requirements.
• Students could make packaging for their soap and test it to see whose is best at protecting the soap inside.
• You could add some extra complexity to the activity – e.g. ask the students to make soap on a rope or soap with a toy inside.

Links to everyday life

Soap

Evidence suggests people have been making soap since 2800 BCE. Over the years and with new scientific discoveries approaches to making soap have changed, as have its uses. It has now become an everyday item rather than a luxury product.

Bar of 'Sunlight Soap' c.1890-1914 

Chocolate

Chocolate behaves in a similar way to soap: when you heat it the bonds between the molecules change so that it becomes more like a liquid; when it is left to cool down it returns to its original form.

A chocolate factory at work, Liebig trade card, early 20th century.

The science – an introduction

Soap is made up of sodium or potassium salts of fatty acids. It is an alkali that also contains glycerol.

When hot water is added to the soap, the heat of the water affects the bonds between the soap molecules, allowing them to move more easily and making the soap mouldable. This is a reversible change and is a result of the type of bonds within the soap. As the soap mixture cools down the bonds begin to return to their original form, giving it a more solid structure which solidifies further when the soap is left to dry, as the water content slowly evaporates. You can melt grated soap over a heat source rather than adding hot water, but we recommend the method above as it is easier and safer in the classroom. There are other materials that behave in a similar way, including chocolate.

STEM club links

These resources support integrated Science, Technology, Engineering and Maths activities in STEM clubs. Here are some specific links:

Science

• Introduces empirical investigation skills.
• Illustrates the concept that science is often about trial and error to find the best method.
• A simple example of reversible changes.

Technology and Engineering

• Use design technology in creating protective and decorative packaging.
• Investigate the best moulding methods – extend this by making moulds using plastic, foil-coated card, balloons, etc.

Maths

• Work out unit costs and profit margins. Allowing for waste and unsold products, what is a good price? How did you decide this?

Curriculum links

This resource has been developed specifically for use within Key Stage 2 and 3 STEM (Science, Technology, Engineering and Maths) clubs to provide enrichment and extension of the curriculum. However it may also be used for teaching other elements of the curriculum at KS2 and 3 in an engaging, inspiring and memorable way.

Key Stage 2

SC1 Scientific enquiry
Investigative skills – planning

• Ask questions that can be investigated scientifically and decide how to find answers.
• Think about what might happen or try things out when deciding what to do, what kind of evidence to collect, and what equipment and materials to use.
• Make a fair test or comparison by changing one factor and observing or measuring the effect while keeping other factors the same.
• Obtaining and presenting evidence.
•  Use simple equipment and materials appropriately and take action to control risks.
• Make systematic observations and measurements, including the use of ICT for logging data.
• Check observations and measurements by repeating them where appropriate.

Considering evidence and evaluating
Students should be able to:

• Make comparisons and identify simple patterns or associations in their own observations and measurements or other data.
• Use observations, measurements or other data to draw conclusions.
• Decide whether these conclusions agree with any prediction made and/or whether they enable further predictions to be made.
• Use their scientific knowledge and understanding to explain observations, measurements or other data or conclusions.
• Review their work and the work of others and describe its significance and limitations.
  

SC3 Materials and their properties
Grouping and classifying materials

• Recognise differences between solids, liquids and gases, in terms of ease of flow and maintenance of shape and volume.

Changing materials

• Describe changes that occur when materials are mixed (for example, adding salt to water).
• Describe changes that occur when materials (for example, water, clay, dough) are heated or cooled.
• Reversible changes, including dissolving, melting, boiling, condensing, freezing and evaporating.

Key Stage 3

Key concepts
1.1. Scientific thinking
a. Using scientific ideas and models to explain phenomena and developing them creatively to generate and test theories.
b. Critically analysing and evaluating evidence from observations and experiments.

1.4. Collaboration
a. Sharing developments and common understanding across disciplines and boundaries.

Key processes
2.1. Practical and enquiry skills
a. Use a range of scientific methods and techniques to develop and test ideas and explanations.
b. Assess risk and work safely in the laboratory, field and workplace.
c. Plan and carry out practical and investigative activities, both individually and in groups.

2.2. Critical understanding of evidence
a. Evaluate scientific evidence and working methods.

2.3. Communication
a. Use appropriate methods, including ICT, to communicate scientific information and contribute to presentations and discussions about scientific issues.

Some useful links for more information

• To find out more about different methods of making soap, try the Teach Soap website.
• To learn more about the chemistry of soap-making and the history of soap, try the Soap and Detergent Association website.

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