Frozen red cabbage indicator

We had a bit of red cabbage left in the fridge and I was keen to do something different to our usual indicator experiment (as we've done this a lot!). I have been freezing portions of red cabbage cooking liquid to save time and red cabbage buying given regular requests to play with the indicator. The frozen portions gave me the idea to try and freeze a large thin sheet of it on a plate and let the boy use it frozen. I hoped it might show more clearly the colour change as the acid or alkali hit the indicator as it would be slower to mix more widely.

I also decided to make it a challenge to identify which solution was which, so I made a tube of vinegar (acid), one of bicarbonate of soda (alkali) and one of just water.

I put the frozen disc of indicator in a washing up bowl and told him what it was. I explained that he had three tubes and I wanted to know which was which.  

He readily accepted the challenge, picked a tube up, took the lid off and told me it was acid. I think he probably knows the smell of vinegar by now, but I asked if he was sure. He took a twisty dropper and squirted some on the red cabbage indicator disc. It partially melted and turned pink.  He promptly declared proudly "it must be the acid because it's turned the indicator pink", and he was of course correct! He then explored the other two tubes, also correctly identifying which was water and which was alkali. His squirting made some pretty swirls of colour in the bowl as the partially melted indicator and solutions mixed, and some bubbles (carbon dioxide) where the acid and alkali reacted. I was pleased that it worked nicely and he enjoyed it.  

Frozen red cabbage indicator

He wanted to do it again, and as I'd frozen two plates (of the IKEA plastic variety), I got another one out of the freezer.  With the second one, we talked a bit about the melting ice and I asked whether the liquid coming off it would be warm or cold and he correctly thought cold. I asked how you could melt the ice faster, expecting him to suggest putting on warm water but instead he decided to demonstrate pouring in all of his solutions rather than squirting them slowly... He wasn't wrong, but it did rather curtail how long the activity lasted! I should think through my questions better in future...

All in all, a nice variation on the usual red cabbage indicator experiment, both with the frozen indicator but also introducing an element of working out for himself which solution is which using his knowledge of how the indicator changes colour.