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Elliot and the Surfing Scientist: Red cabbage pH experiment

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Drinking glasses in a row, filled with various liquids, labels read 'vinegar', 'lemonade', 'lemon juice', 'washing powder'
Elliot and the Surfing Scientist: Red cabbage pH experiment

SUBJECTS:  Science

YEARS:  3–4, 5–6


It might sound 'un-sciencey', and have a bad smell, but red cabbage is actually very useful for testing the pH of liquids.

Added to well-known liquids like lemonade or vinegar, red cabbage juice changes to 'pretty colours'.

In this science experiment the Surfing Scientist Ruben Meerman explains the colour changes and how red cabbage juice indicates if a liquid is an acid or a base.


Things to think about

  1. 1.The pH of a liquid tells us if it is an acid or a base. Do you know any acids or bases? Predict whether the following liquids are acids or bases: baking soda in water, vinegar, lemonade, lemon juice and washing powder in water. Draw up a table listing your predictions and add your observations as you watch the clip.
  2. 2.What does Ruben say a pH indicator is? What colour will the pH indicator (red cabbage juice) turn when added to an acid? What colour will it turn in a base? Record in the table what you 'observe' when the cabbage juice is added to the five liquids. In lemonade, what is it that turns into carbonic acid?
  3. 3.Compare your predictions with the observations you made during the experiments. Can you think of some other liquids you could test? What might happen to the pH of lemonade if you added baking soda?
  4. 4.Ask an adult to make some red cabbage juice pH indicator. They will need to boil two cups of chopped red cabbage in water for ten minutes, and then strain off the liquid when it has cooled. Add this cabbage juice to different liquids to test their pH. Complete a table of predictions and observations for your tests.


Acknowledgements

Image credit: 'chopped red cabbage II', courtesy 19melissa68 (Flickr).


Production Date: 2008


Copyright

Metadata © Australian Broadcasting Corporation and Education Services Australia Ltd 2012 (except where otherwise indicated). Digital content © Australian Broadcasting Corporation (except where otherwise indicated). Video © Australian Broadcasting Corporation (except where otherwise indicated). All images copyright their respective owners. Text © Australian Broadcasting Corporation and Education Services Australia is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License (CC BY-SA 4.0).

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