Citrus fruit and citric acid

I recently bought a cheap box of mixed citrus fruit, and the boys helped to make a delicious cake using one of each of the fruits (lemon, lime, orange and clementine). After we grated the peel for the cake, we tried guessing which was which from the smells with our eyes closed. I'm not very good at this, and there was a lot of peeping, but they got the hang of it!  We talked a bit about how our nose helps us understand the world around us as we can tell different smells apart from each other.

We also had lots of fun juicing each type of fruit and tasting them, with the boys trying to describe the taste of each.  We moved onto making flavour combinations too, and trying to work out (largely unsuccessfully!) what was in each.  We talked a little about how taste is another of our senses which help us understand our surroundings.

When we'd used most of what was edible, we did a quick experiment with some bicarbonate of soda solution - are they all acidic?  We've tried this with lemons and oranges before, although I think they only remembered the lemons.  However the answer is yes, they all contain citric acid!  This gives a nice fizz as it reacts with the alkaline bicarbonate of soda solution in a chemical reaction that makes carbon dioxide.  The setup wasn't really such that we could compare how acidic each fruit was as there was a variable amount of juice left in each.

They found that after a while, however much bicarb solution they added, they didn't get a fizz, and the big one and I discussed how the acid must have been used up and there wasn't enough left to react any more. They had lots of fun, and we all enjoyed the cake we made too!