The Many Many Questions in Miranda's Mind

Baking Powder Joy

Miranda's favourite part of  "Doing Science" is making fizzy messes with baking powder and vinegar, and she happily dons her enormous plastic safety goggles just in case. In various guises, this experiment has been repeated so frequently that the reaction is completely expected, yet the fun of making her own mini volcano cannot be beaten. Recently, it got a bit more involved and she started asking what was actually happening.

"Why does it fizz Mum?"

"Well, the vinegar is a sort of liquid called an acid. Really strong acids kinda eat away at things - some of them will poison you or make your skin itch and burn. But the weaker ones you can use to clean things because they eat all the yuk. Daddy put vinegar in the kettle the other week, and the vinegar ate all the yuk inside it."

"Eww. Vinegar tea."

"Yep well you do rinse it out afterwards."

"Yuk"

"Anyway. Baking powder is called a Base."

"A bass?"

"No, b-a-s-e.  It's another word for alkali. It's like the opposite of an acid."

"So baking powder and vinegar are opposites."

"That's right. And when they get together, they fight. It's called a chemical reaction. They don't like each other, and give off a lot of energy fighting each other. That's what you can see in the fizzing and bubbling."

"But why does it bubble? Why doesn't it catch fire?"

"Some chemical reactions do catch fire, but I wouldn't let you make volcanoes with things that actually caught fire."

"It would make cool lava though."

"That's true. But when vinegar and baking powder fight, they actually join together and make different things. They make water, a type of salt and a gas called CO2, which is what is in the bubbles."

"I don't see any salt or water."

"No, the salt is dissolved in the water so you can't see it, and it is water that the gas bubbles form in - you can't make dry bubbles, can you? It stops fizzing when all the baking powder and vinegar has turned into water and salt and gas. That's why your volcano tube is empty when it's stopped fizzing."

"Why is it called baking powder?"

"Because you use it in baking. It makes your cakes into cakes, not pancakes or pudding. When you mix it in to cakes, the same thing happens - it fights with other cakey ingredients and makes bubbles, which push upwards and make the cake rise."

"Like bread?"

"Errr... no, that's yeast, but its the same sort of thing."

"Wait does that mean cake is full of salt and gas?"

"Ummm... technically yes. But its such a small amount of salt that you can't really toaste it when you've put so much sugar in. I did make HORRIBLE cupcakes once though, I put way too much baking powder in and they came out enormous and tasting of baking powder. Not good."

"Where does the gas go? I don't pop all the bubbles."

"No, you don't need to. It just ends up in the oven I suppose, or disappears into the air. You can see it though, if you blow real bubbles on it. If you get your bubble bottle and blow bubbles over the volcano, they just sit on top of the volcano gas, they won't land on it and pop."

"How come?"

"Because the baking powder bubbles are full of CO2, which is a bit, sort of heavier than normal air. So the normal air in the bottle bubbles sits on top of the baking powder bubble gas, and they don't go down and hit the volcano and pop."

"I don't think that would work."

"Try it!"

We do try it. And it doesn't work. Typical! However, this time I let her put green food colouring in the vinegar so now she has green fizzing goo in her volcano, and all is well with the world.