Didn't sound likely to me but the boys were insistent. The boy imparting this factoid was at least 12 years old and therefore probably a genius with very bad teeth; certainly cleverer than me as I am a mum and therefore know nothing. Apparently.
Insults aside I decided they could prove it to themselves. Theory was the place to start - we talked through characteristics of acids, bases and what the pH scale is. We briefly looked at hydrogen ions but I lost W so it was time to get practical and we followed the Stanford Uni experiment (link below).
I pre-made the cabbage water and the kitchen smelt horrendous; then we assembled a bunch of household objects :
- Bicarbonate of soda (dissolved in water)
- Distilled water
- Cola
- Lemon juice
- Apple juice
- Vinegar
- Bleach
- Shampoo
- Anti-bac hand gel
The boys predicted whether each liquid was going to be acidic or alkaline based on their characteristics (sliminess / bitterness / sourness). The boys tasted the lemon juice and bicarb just for my own entertainment. "Can we pleeease drink the Coke?" Only if it turns out to be less acidic than water.
With our cabbage water ready we started adding our various liquids, comparing the colour of the cabbage water to our chart to see what the approximate pH was and writing up our results as we went.
We got a really fantastic range of colours and the bleach finally overrode the kitchen cabbage smell which was a relief for everyone.
If you've got your own science lab the BBC has the experiment nicely explained here:
http://downloads.bbc.co.uk/schools/teachers/bang/bang_tp_red_cabbage_indicator.pdf
If you're a kitchen table scientist then take a look at this brilliant PDF from Stanford Uni:
http://web.stanford.edu/~ajspakow/downloads/outreach/ph-student-9-30-09.pdf
