Friday, 1 November 2013

Halloween carrots, science and art

 This year our local supermarket was stocking purple carrots called 'Witches Noses'.  This might sound like some kind of GM Frankenfood, but actually orange carrots are the more recent type (17th Century) prior to which they were purple.  The purple carrots we bought were a modern breed, but it's nice to support a greater variety of vegetables than we have been used to seeing.  The purple colour is caused by anthocyanins which you may have heard of because they are a group of antioxidants also present in fruit such as blueberries and credited with all sorts of health enhancing properties.

The colour was so strong it bled and made soup look a bit unappetising , and when we ate them raw we ended up with stained fingers I cooked the last batch of them on their
own by simply boiling in water.  This produced a deep purple liquid and made me wonder if it would make a good indicator solution in the way that red cabbage water
does.  A quick shake of vinegar in a sample on a spoon later and my hopes were confirmed, so I saved the juice for some after dinner fun.

I started by pouring a couple of tablespoons of the carrot water onto a plate and giving the kids vinegar and bicarbonate of soda to add to the liquid.  It's better to start by letting children experiment and make observations by themselves without telling them what to expect at first.  You can draw out their observations with comments and questions 'wow, look at that, what colour did it go when you added the vinegar? Now what happens if you add bicarb?'

Once they've had a few goes turning the solution to red, blue, back to red you can start to introduce some of the correct terminology.  Here's roughly how I explained things as we went along:  The liquid is an indicator solution. Indicator solutions change colour if you add an acid or an alkali.  They
'indicate' which means they show you whether you have added and acid or an alkali.  Our indicator solution goes pinky red when you add an acid and blue when you an an alkali.  Vinegar makes the solution go red, so do you
think it is an acid or an alkali?  Taste the vinegar, what does it make your
mouth feel like?  What else makes your mouth feel like that? Lemons? Brilliant, lets see what happens when we add lemon juice.  The bicarb made the solution go blue, so do you think it's an acid or an alkali? Alkalis sometimes feel soapy, what else can we test that feels soapy? ...

After the boys were in bed, I dipped some strips of paper in the remaining solution, then added some salt as a mordant (something that fixes a dye) and boiled some cotton rag in it for a few minutes, cold rinsed it and then hung it to dry.  I wanted to make indicator strips, and thought it might work to make 'permanent' indicator fabric which we could play with, rinse out and use again another day since purple carrots are a rarity in the shops if we wanted to repeat the experiment.  I found the paper I had cut up from an old envelope must have been a bit posh - acid free -as it went blue.  The cotton dyed beautifully, so we were all set for the next day.

 This time I lined up some safe, everyday household items to test, including milk, washing up liquid, more bicarb mixed with water, vinegar and some carbolic soap scrapings mixed with water.  Ollie added most of them himself to glass ramekins and then dipped a strip of indicator fabric into each one, laying the dipped strip in front of the relevant ramekin.  At the end, we talked about what colours they had gone, how light or dark a change and what the colours meant.  Getting it right whether the colour indicates it is an acid or an alkali is very hit and miss for Ollie, but even for him I would have been surprised if he remembered all of it first time.  This activity is just about enjoying making things change colour and introducing the words for young children, as they get older you can focus more on the science of what is going on.  You can even baffle older kids with the irritating statement that all alkalis are bases, but not all bases are alkalis (alkalis are just bases that can be dissolved in water, and not all bases can be dissolved in water).  Even little ones Toby's age enjoy seeing the effect they have on the colours by dipping them into different liquids, and will likely at some point start mixing the liquids together in experiments of their own design.  With Ollie we also keep a little science experiments log book because he likes to look
back on the experiments he's done before.  Sometimes he'll add drawings of the experiment, today he
was happy to supply reminders about what colours things had turned, what that meant, and to chose some
different coloured strips to stick in.

 When we had suitably covered the dining table in multicoloured gloop, I had a quick wipe down and gave each of the boys a square of the indicator fabric, a ramekin of vinegar and another of bicarb in water.  They had free reign then to create whatever took their fancy - at first dipping chopsticks daintily into the liquids and onto the fabric, then using their fingers, and finally pouring the liquids out completely.  They were really pleased with their finished artworks and I think they're so pretty I'm going to pop them into frames so we can see their science and art up on the wall.  I don't know how well the colours will keep, but then, that's just another experiment.

If you can't find purple carrots (which is fairly likely) then this works well with the liquid saved from boiling red cabbage.  Letting kids choose what the want to test really gets them involved in the whole activity, but make sure you stress that they don't try out the things that lurk under the kitchen sink for example if you use things like bleach in your home.  I'm working on the assumption with kids of the age of mine are that telling them not to put thing in their mouth is not fail safe, so I opt for things which are either edible, or at least won't do them any harm if ingested in small amounts, such as soap. If you make up just liquid indicator it will keep in the fridge for a couple of days, the paper strips and fabric for a lot longer so long as they're kept dry.