Fizzing leftover lemon

On my birthday, I enlisted the 'help' of two small boys to make me a cake.  Well, the smallest provided musical accompaniment with an old tin and a spatula, and the biggest attempted to help, whilst making an enormous mess!

It was a lemon cake, and we ended up with four half lemons that had been juiced and some leftover lemon juice, as well as a pause in the baking process which needed something to fill the time.  After some very sour lemon juice had been consumed at the eldest's request, and some funny faces pulled as a result (the baby tried some too, as he wanted to grab his brothers, and his face was also a picture!), I decided to set up some quick science fun.

I put the lemon halves in a bowl, made up some bicarbonate of soda solution in one of our test tubes, and gave the small boy a pipette.  I told him to do what he wanted with it. without squirting anything all over the table or his brother. I thought it would be interesting to see how he played with it, rather than giving him instructions on what to do.

Adding the leftover lemon juice back into the juiced lemon halves
He's come across the reaction between lemon juice (citric acid) and bicarbonate of soda (an alkali) before, notably when we did it in film canisters and blew the lids off, and he said he wanted to make it fizz.  He went about it by filling the juiced lemon halves with the remaining lemon juice, then squirting in the bicarbonate of soda.  I'd thought he might just go straight for tipping the bicarbonate of soda in the lemon squeezer so I was pleasantly surprised that he went for a less messy approach!

It fizzed to his satisfaction, and amused his brother, and then he did it again, and again, until the citric acid ran out and each addition of bicarbonate of soda solution resulted in very little fizzing.  He then had a bit of a poke of the lemons, told me the bowl was full and announced he'd finished.

Fizzing when he added bicarbonate of soda solution

I asked him to explain what he was doing to his brother, and he told him he'd made bubbles of carbon dioxide gas.  Whilst clearly not something a 10 month old is going to understand, it was nice to see that the big one had remembered which has the chemical reaction was making.  His brother was also quite entertained by the fizzing, and gave the big one a round of applause!

A short activity, but easy to set up and a good use of juiced lemon I'd have otherwise thrown in the food waste bin, and it filled the time nicely.