I am not a chemist. But I am curious...
This evening I was making ingredients for a "lemonade bar", where people mix various flavors into a lemonade base to create custom flavors (mint + cucumber is a favorite, strawberry + ginger is another).
I wanted to offer "really sour" as one of the mix-ins, so I put about an ounce of food-grade powdered citric acid in a jar and added enough apple juice to make it dissolve [see note]. I shook it vigorously, and as the citric acid dissolved, I noticed that the jar got fairly cold.
That's neat! So what's the process that makes apple juice + citric acid get cold?
(For extra credit: are there other kitchen counter endo- or exo-thermic reactions I should try with my six year old son?)
I just repeated the experiment mixing tap plain water and citric acid. It was also endothermic, dropping the water temperature from 21.5 to 11.5 celsius.
[note] And yessir, it's really sour! :)