Want to drink milk, but worried about all the proteins in it disrupting your digestion? Want to drink Coke, but worried about all the acid in it ruining your teeth? Here's a drink that's perfect. You just need to repress your gag reflex.
Here's an experiment that will have you thinking about what's in your drink. Not that what's in your drink is such a bad thing. What's in the milk pictured above is nothing more than a bunch of proteins which include calcium. Calcium is great for you. What's in the Coke is phosphoric acid. This is also not terrible. Coke has a pH of about 2.53, which isn't too much lower than orange juice (2.80) and is higher than some of the sharper juices, like cranberry juice (2.30-2.52).
We all know what happens when acid, even relatively mild acid, makes contact with milk. The milk curdles. When Coke is mixed with milk, the phosphoric acid goes to work and milk curdles into little clumps. What's surprising is what a change that reaction makes to the Coke. The Coke loses its phosphoric acid, which teams up with calcium atoms from the milk to make tricalcium phosphate and hydrogen.
3Ca + 2H3PO4 —> Ca3(PO4)2 + 3H2
The tricalcium phosphate precipitates out of the liquid and settles on the bottom. And nearly all of coke's color goes with it. We're left with a bottle that is full of liquid made from Coke and milk juice, with the acid and protein clumped together and out of the way. And there's probably a lot of hydrogen gas dissolved in there. Sounds great to me!