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Delving even deeper into our digestive system, today we will look at how acids and alkalis work in the body. 

Thank you to Evie for this suggestion. 


Carry out an experiment into how acids and alkalis work in our digestive system.  

Watch the video above and then follow these instructions. 

-        Materials needed:

o   5 numbered cups containing water, baking soda solution, white vinegar, clear washing up liquid solution, lemonade

o   Table of results 





Washing up liquid

Bicarbonate of soda solution













o   Cup of red cabbage indicator (water preserved from boiling red cabbage)

o   (optional) pipettes

-        Predict what you think the pH value of each of the substances to be used in the experiment – which are acid/alkali/neutral? Use the pH scale on the PPT slide. 

-        Working one substance at a time, add a little indicator solution to the pot (either with pipettes or by pouring gently – roughly 1:5 indicator:substance ratio) and observe the colour change.

-        Use the pH scale to determine the pH and record it on the results table.


In context of digestion: saliva is neutral, stomach acid is acidic and bile is alkaline

  • All substances used in this experiment are clear/pale in colour – so colour alone can’t always help us distinguish different substances apart – hence the need for the pH experiment!