Colour and chemistry with red cabbage

Back in the day, I remember a heated dinner table discussion about the pH of kiwi fruit with my Dad, and using some universal indicator to find out who was right. I suspect this wasn't a universal childhood experience (excuse the pun...) but there's no reason everyone can't have a colourful way to show acids and alkalis at home, and one that's safe for even the smallest scientists.

To make the indicator, I boiled about a quarter of a red cabbage (sliced up) in some water.  The cabbage was served with dinner and I kept the lovely purple liquid.  Given my son calls red Leicester cheese "orange cheese" (he's not wrong...), I suspect it'll be known as purple cabbage in our house before long.

Red cabbage flask
Red cabbage colours in action.
Toddlers love dressing up, and after the apron and chef's hat I made him for Christmas was a success in getting my little helper cooking, I splashed out on a little lab coat and goggles for him from Learning Resources.  These are for age 3-6, but as he's an averagely sized not-quite 3 year old they've got plenty of growing room and the goggles fall off into his experiments. But he loves them and wants to wear them and "do science".  I need to add some elastic to the goggles to hold them on for now... Anyway, a lab coat isn't necessary, although I wouldn't wear your best clothes as I'm not sure purple cabbage stains always come out.  The goggles are handy for splashes, but you wouldn't wear them to put vinegar on your chips so they're not necessary either.  But it wouldn't be dressing up and "doing science" without the outfit...  One day I'll explain that science doesn't have to be about test tubes and lab coats!

We had oodles of fun turning the red cabbage water from purple to pink, back to purple, and on to a dark blue.  And then back again. And again.

Acids turn it pink, so either vinegar or lemon juice work well.  Bicarbonate of soda dissolved in water is a nice kitchen alkali to use.

We went for fairly dilute solutions and lots of pipetting because my toddler loves the pipetting as much as the colour changes. The pipette we used is a 'jumbo dropper' from Learning Resources.  Again, not strictly necessary as you could just pour liquids, but a lot of fun, and it's designed for little hands so my toddler got the hang of it very quickly.  We also used the test tubes and conical flask from the set as it's also part of "doing science" as a fun activity he asks to do, but any empty plastic tub would work just fine - best if it's clear and you can put something white underneath, or if the tub itself is white. Glass containers would work fine with an older, less clumsy child.
Red cabbage colours
Red cabbage cooking water with (left) bicarbonate of soda, and (right) vinegar

I have some more ideas for things we can do with the red cabbage indicator, but those will need to wait until another day.  The nature of toddlers is that they like repetition, so we'll be doing this one a few times in the next week or so!


Comments

  1. A couple of reflections on this a little over a month on from when I wrote it... Firstly, I was right about the repetition, we do this almost daily, but it's not much hassle if you've got some red cabbage cooking liquid frozen in an ice cube tray and can pop a cube out and microwave to defrost it quickly. Secondly, it's been brilliant for improving the small boy's hand-to-eye coordination with pouring, and his fine motor skills with using the pipette.

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  2. We had lots of fun with this! The fizzing when you add bicarb to the cabbage water and lemon juice mixture was a fun extra.

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    Replies
    1. Fantastic! Watch out for another experiment soon that makes use of the fizzing, I've tried it out but not yet had a go with the little ones...

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