Bath Fizzers

Make your own bath fizzers and see whose fizzes the most!

Year groups: 3-11 (ages 7-16)

Educational objectives

For each student to make two bath fizzers and test their performance, investigating the best proportions of ingredients to get the ultimate ‘fizz’.

Key student learning

Sodium bicarbonate reacts with citric acid when dissolved in water, releasing bubbles of carbon dioxide, water and a salt.

3NaHCO₃ + C₆H₈O₇ --> C₆H₅Na₃O₇ + 3CO₂ + 3H₂O
(sodium bicarbonate) + (citric acid) --> (sodium citrate) + (carbon dioxide) + (water)
When an acid (the citric acid) and a base (the sodium bicarbonate) react, the resulting reaction always produces a salt.
Dry chemicals and solutions can behave differently.
Witch hazel can be used when moulding the fizzers because it evaporates quickly, so the water in it does not allow the reaction to start fully.

Materials per group

Latex-free gloves
Goggles and lab coats
Bowl or wide-topped beaker, at least 500 ml capacity
Mixing utensils (forks, whisks or spatulas)
At least one plastic pipette (5 ml capacity)
500g of sodium bicarbonate powder (from either chemical or baking supplier)
250 g of citric acid monohydrate (available from chemical suppliers or can be ordered from some high street chemists)
Spray bottle, at least 250 ml
Witch hazel solution (available from chemists and some supermarkets; sold as a ‘natural’ antiseptic)
Food colouring
Food flavouring and/or fragrance oils (e.g. vanilla essence, lavender oil)
Scales

Optional

Glitter for decoration
Scoops and/or moulds (e.g. biscuit cutters)
Pack of paper cake cases (approx. 100 cases)

Practicalities and safety

This activity works well if students are in groups of three or four.
As with any activity using chemicals, check that members of your group do not have specific allergies.
We advise wearing protective clothing (lab coats or aprons), gloves and goggles for this activity.
As chemicals are being used we would recommend the use of disposable gloves, or alternatively at the points where you need to handle the mixture you can use a plastic bag to cover your hand or cling film to form the mixture into the required shape.
Some teachers have found it beneficial to do a demonstration first so that students understand exactly what they are doing.
Making the bath fizzers will take approximately 20 minutes.
The amounts of materials are for guidance and need not be followed exactly.
Once bath fizzers have been made there is a chance that they will grow, so make them slightly smaller than needed.
Ensure that you can store the bath fizzers until your next session as they will need about 24 hours to dry out fully.
If you want to make bath fizzers with different colours or smells you will need to separate the mixture between step 3 and step 4.
In step 7 you should add only a couple of squirts of witch hazel to the mixture; it should not be wet. If too much witch hazel is added the mixture will start to react and ‘grow’. If this happens do not add any more liquid and mix well to encourage evaporation.
If the mixture has partially reacted, the fizzers will still work, but not as well.

Discussion

What makes the best bath fizzer?
What is the best recipe for bath fizzers?
Are there any considerations that need to be taken into account before a product like this is sold?
Why is it safe to have acid in a mixture that people use in the bath?
Do bath fizzers clean you?
What is the chemical reaction in the bath fizzers – why does it only happen in water?

Extensions

The groups could consider packaging for their bath fizzers – this could include wrapping the bath fizzers in tissue or net curtain, or making boxes.
You could hide toys or dried flowers in the centre of the bath fizzer, so that when it dissolves you get a surprise.
The bath fizzer could be used to look at different themes with different age groups; for example you could use green food colouring to make a cauldron effect.
You could link this activity to ‘young enterprise’ where you make the fizzers as a product to sell within the school.
You could extend this activity by setting each group the task of working out the optimum way to make bath fizzers, whilst considering investigation methodology, e.g. it is important to change only one variable at a time, ensuring a fair test, recording actions and the results.
Additional investigations could include the best proportion of sodium bicarbonate to citric acid, the best way to add the colour and fragrance, the best mixing method (utensils, hands, shaking, etc.), the best way to mould the bath fizzers, and the best packaging to make the fizzers look good and protect them until use.
In another session you could test the bath fizzers, and choose which one students think is the best from the different investigations above. From the results of this you could create the ultimate bath fizzer recipe.
You could visit different shops that sell bath fizzers and find out how theirs are made and what they put in them.
If you are using this as a science club activity you may want to sell the bath fizzers to provide financial support for science club sessions.

Links to everyday life

Bath bombs or bath fizzers are sold in many cosmetics shops around the world. They are therapeutic during bathing because of the essential oils that they contain and are also used for cleansing.

Effervescent vitamin C tablets use a reaction to create ‘fizz’ in a similar way, to disperse the contents evenly throughout a glass of water.

The science – an introduction

Bath fizzers fizz in water because the sodium bicarbonate reacts with the citric acid. This releases bubbles of carbon dioxide and produces a salt and water:

3NaHCO₃ + C₆H₈O₇ --> C₆H₅Na₃O₇ + 3CO₂ + 3H₂O
(sodium bicarbonate) + (citric acid) --> (sodium citrate) + (carbon dioxide) + (water)

The reaction only starts when the two dry chemicals dissolve in the water – i.e. it is the solutions reacting. However, when you add any liquid, such as food colouring, to the mix, then your mixture may begin reacting early. You can use the activity to introduce the idea that dry chemicals and solutions can behave differently.

Witch hazel is a suitable liquid to use when moulding the fizzers as it evaporates quickly. The witch hazel solution only minimally dampens the dry ingredients for a short time, conserving the ‘fizz’ for when you want it in the bath!

STEM club links

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

Science

This activity introduces the idea that dry chemicals and solutions behave differently by investigating the different ingredients of the mixture.
Evaporation and the fact that witch hazel is a suitable liquid to use for moulding the fizzers can also be investigated by using other liquids which have different rates of evaporation.

Technology

Creating packaging for the bath fizzers from different materials available in school.

Engineering

Examining the quality of different types of packaging and deciding what shape/material would withstand the greatest force so that bath fizzers reach customers undamaged.

Maths

If you introduce a youth enterprise element, club members could plan to market and sell the bath fizzers. Work out unit costs and profit margins.

Curriculum links

This resource has been developed specifically for use within Key Stage 3 STEM (Science, Technology, Engineering and Maths) clubs to provide enrichment and extension of the curriculum. However it may also be used for teaching elements of the curriculum at KS2 and KS4 in an engaging, inspiring and memorable way.

We do not recommend this resource for use with children younger than KS2 owing to the safety requirements.

Science Curriculum links from QCA guidance for England.

Key Stage 2

Ideas and evidence in science: It is important to test ideas using evidence from observation and measurement.
Investigative skills: Plan, obtain and present evidence; consider and evaluate evidence.

This activity also provides a great opportunity for cross-curricular learning linked to Art, Design, Maths and ICT (which could be used to record results and/or design and produce packaging).

Key Stage 3

Key concepts
1.1. Scientific thinking
1.2. Applications and implications of science
1.3. Collaboration
Key processes
2.1. Practical and enquiry skills
2.2. Critical understanding of evidence
2.3. Communication
Range and content
3.2. Chemical and material behaviour
Curriculum opportunities
The curriculum should provide opportunities for pupils to:
a. research, experiment, discuss and develop arguments
c. use real-life examples as a basis for finding out about science
f. use creativity and innovation in science, and appreciate their importance in enterprise
k. make links between science and other subjects and areas of the curriculum.

This activity supports delivery of How Science Works as it allows pupils to explore science in use in the ‘real world’ in a product they may have personal experience of. It allows them to experience the scientific method and to understand that different scientists will have different views of the ‘best’ result (when coming up with their fizzer formula different student groups may set different criteria for success). They will also learn to apply some key concepts about rates of reaction and reaction between acids and bases (neutralisation).

Key Stage 4

How Science Works
1.1. Data, evidence, theories and explanations
1.2. Practical and enquiry skills
1.3. Communication skills
1.4. Applications and implications of science
Breadth of study
2.2. Chemical and material behaviour

Some useful links for more information

If you go to the US PBS (Public Broadcasting Service) website you can register for free access to more films like this one about making lipgloss.

The Science Museum cannot be held responsible for the quality or accuracy of the content of web pages from other sources.