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Curdling Coke

img_3013I just signed the contract so I can finally let you know – I’m writing another book!

My editor, Joe, from my previous books has a new gig and brought me on to write 365 Weird and Wonderful Science Experiments with MoonDance Press. I am  excited to be writing again but boy oh boy – 365 is a LOT of experiments! And the extra challenge is that all these projects need to be doable by kids WITHOUT the help of their parents.

So I’ve been poking around to see what weird and wonderful things I can come up with, trying out all sorts of projects and filling up my kitchen counter with balloons, straws, bottles of dish soap, hydrogen peroxide and the other paraphernalia of home experimenting.

Here is one surprisingly simple little investigation I thought I would share.

Pour yourself a glass of cola. Add in a tablespoon or two of milk. I used 2% milk and full strength cola.

And wait.

After about 15 minutes you will see dark foamy clumps near the bottom of the bottle. The milk is curdling in the cola. Phosphoric acid in the cola is reacting with calcium in the milk and causing it to clump together along with caramel coloring and other parts of the milk.

The main chemical reaction is calcium reacting with pohosphoric acid to create tricalcium phosphate and hydrogen gas. Or for the chemists:

3Ca + 2H3PO4 —> Ca3(PO4)2 + 3H2

After an hour the bottom is full of the dark, denser, curdled milk and the clear top layer is mostly just water and sweetener.

I left the glass out overnight and in the morning the top portion was perfectly clear. All of the coloring and opaque milk parts had sunk to the bottom.

A similar reaction actually happens inside your body. Drinking lots of acidic cola makes it harder for your body to absorb calcium like that in milk and some studies suggest it increases your chances of getting osteoporosis (weak and brittle bones).

So this brings up some questions.

Does the same thing happen if you add milk to root beer or other dark colored sodas. If so, does the ice cream in a root beer float do the same thing if you let it set too long?

Does it matter what kind of milk you use? How about skim or half & half?

What can you do to speed up the process? How about heating up the cola? or stirring the milk?

And of course, if you are a kid age 7-10, how does it taste?