Science/Chemistry KS2/KS3: How to make the fizziest bath bomb

This is an effective example to illustrate the way that scientists work, in devising a fair test and collecting evidence to inform their conclusion.

The reaction between sodium bicarbonate and citric acid is demonstrated and explained.

The products of the reaction are carbon dioxide gas and salt.

The children carry out an investigation to find the best ratio to use to make the fizziest bath bomb.

They design a fair test, deciding what variables they will need to keep the same (temperature of water, amount of mixture, size of bath bomb), which one they will they will change (ratio) and what they will measure (volume of carbon dioxide gas).

The children then carry out the experiment and present the results to identify which ratio produces the most gas.

The scientist then introduces another factor to be considered – how long the fizz lasts.

The final decision as to which ratio is best is then made.

This film is from the BBC series, Operation Awesome, in which primary pupils explore a range of amazing practical science challenges with presenter Steve Mould.

Teacher Notes

Key Stage 2:

This could be used as an effective example from a real-life context to illustrate how to design a fair test.

Pupils could be asked to identify the different types of variables involved and justify the decisions taken in the film.

They could be asked to identify risks and how these have been addressed.

They could be asked to present the results from the experiment as a graph.

Pupils could then be asked to evaluate the method and to suggest how we could make the results more reliable (for example, by taking repeat readings).

Key Stage 3:

This could be used as an effective example of a real-life context where scientists need to design a fair test.

They could identify the control, dependent and independent variables.

They could evaluate the method and suggest improvements to improve the accuracy and precision of the results.

They could present the results as a graph and discuss the reliability of the data and how it could be improved.

They could be asked to write a word equation or a balanced symbol equation for the chemical reaction between sodium bicarbonate and citric acid.

Curriculum Notes

This film will be relevant for teaching primary science at Key Stage 2 or Second Level in Scotland or chemistry at Key Stage 3 or Third Level in Scotland.

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