pH of foods

It's been a while since we had a play with red cabbage as a pH indicator, and my youngest son is getting into "doing science" too, so I bought another cabbage.  I set up the same thing for both of them, but asked my 4 year old more questions to try and prompt him to predict what would happen a little more as he's got more knowledge and experience to draw on.

I chopped up various foods (some acidic, some closer to neutral) and put a tub of bicarbonate of soda out.  My children had a tub of red cabbage cooking liquid each, made by grating red cabbage, adding water and heating in the microwave for a couple of minutes before straining,  I usually use the leftovers from cooking it to eat to minimise waste, but this time I used a small piece and grated it so more colour comes out.

Various foods and red cabbage pH indicator

They had some little yoghurt pots, and a children's pipette (from this set - affiliate link), and I asked what they thought would happen when they added different foods to the red cabbage.  My eldest could remember that acids made it pink, and that lemons are acidic.  He tried the different foods, and found that all the fruits turned the purple to various shades of pink.  We got a cocktail stirrer (which hasn't seen the light of day for a few years!) out to squash the foods a bit to release the liquid as in hindsight I didn't cut some of them into small enough pieces to see the best colour change.  Both boys thoroughly enjoyed mashing up the foods in the pots and getting brighter pink, so maybe it wasn't such an error after all!

Lemon turns the red cabbage pink!

The bicarbonate of soda makes an alkaline solution which is blue/green, and both liked adding this to their purple pH indicator.  The big one and I talked a bit about how cucumber and bread didn't make the indicator change so must have a fairly neutral pH, whilst the little one got stuck in to experimenting with making various combinations.  Both boys then collaborated with remarkably little disagreement to make different 'potions', some of which fizzed (because carbon dioxide is produced) and changed colour when the bicarbonate of soda solution was added to acidic fruit and cabbage liquid.  They spent much longer doing this than the more structured activity we started with, but they had fun and worked together, and hopefully both learnt a little from doing it!