Because that is the way a real chemist does it! It really is that much better of a system (IMHO).
Exactly. The volume of something can change based on many factors (is it warm is it cold is it dense is it foamy did you sit on it and flatten it out or blow it up like a balloon) but mass is mass and no matter how much you stretch or squeeze or beat or froth a thing, as long as you don't actually add anything or take anything away, its mass (and also its weight, provided we stay relatively near the planet's surface when we measure it) is never going to change. 100g of whipped cream is a lot "larger" than 100g of fresh cream, but it's the same "amount" of cream either way. If I get 100ml of fresh cream, though, and you get 100ml of whipped cream, we both have "100ml worth" -- they'll both fill the same sized cup -- but at the same time, I've got a lot more cream than you have.
Volume is fine, if you just want to measure the "bigness" of something, just how much of the universe it uses up, sure. But for measuring the actual "muchness", if you really want to measure the actual "amount" of something and not just how big it is, mass/weight truly is the way to go.
