Science for preschoolers and small children, (cont). Here's an easy one that you can do in 3 min. Baking soda plus vinegar gives loads and loads of fizzy bubbles.
This "science trick" loosely demonstrates that sometimes, mixing two substances together gives a reaction. If you like, you can start off with some other mixtures that don't give a reaction, just to hammer the point.
If you mix sand and water nothing happens.
If you mix water and sugar the sugar dissolves, but that's all.
If you mix baking soda and vinegar, you get loads of fizzy bubbles, wow!
We played around with this for about 20 minutes, working out how much we baking soda we could put in the glass without the bubbles fizzing over. In the end we came up with 1 t baking soda and 1/4 c white vinegar.
The chemical reaction here, in case you're interested, is that mixing an acid with a base gives a salt plus water. A byproduct of this reaction is the production of carbon dioxide, which is given off by the baking soda as the acids rip off their hydroxyl group. My kids don't care about that part, and it would kill the fun if I started going on about that anyway. This science trick is all about noticing a reaction occurring.
Okay, that was fun. But do you want to see it in slow motion? Lets use vinegar to react with a different base: an egg shell. The egg shell is made of an alkaline calcium compound. If we drop an egg into some vinegar and leave it a while, the vinegar will dissolve that shell clean off, leaving a funny wobbly shell-less egg.
Here goes: Get a load of this! As soon as you cover the egg in vinegar there are zillions of little bubbles forming. That's the carbon dioxide again, being produced as the acid reacts with the base. All those bubbles make the egg float. It's like watching a lava lamp as it bobs to the top of the jar. The shell starts to dissolve off in layers, see?
After a day, we washed off the last bits of the shell under the tap. It was soft and chalky and washed off with no problem at all. We all held the wobbly shell-less egg.
If you think the kids look a little underwhelmed it's because they are. "That's kind of disgusting Mum", said Harry.
Well, yes it is I guess. Perhaps this is also a lesson in how we do not like it when people use chemicals to mess with our food.
Me: "Yes it's funny to see an egg without a shell. But isn't it cool that the vinegar dissolved the shell off?
Harry: "Um...well I just don't know."