Saturday, October 24, 2009

#2 Sweetened salad dressing

Ok, this one is from GRE Subject test (question number 16) and rather "chemical".
If sucrose and monosodium glutamate (MSG) are added to vinegar and oil salad dressing and shaken, the mixture will eventually separate into two phases of different density and polarity. Where will most of the sucrose and the MSG de located following phase separation?
(A) Both will concentrate in the vinegar
(B) Both will concentrate in the oil
(C) Both will concentrate at the interface
(D) Sucrose will concentrate in the oil and MSG – in the vinegar
(E) Sucrose will concentrate in the vinegar and MSG – in the oil
Show answer
Lets think a bit. The key word in the question for me is "density" and also I can't understand what "polarity" means and what role does it play.
So we will use density approach.
If you google a bit, you'll find – as I did – that oil density is about 0.9 g/ml and sucrose density is 1.5 g/cm3 (=1.5 g/ml) when MSG density is about twice less (lets say 0.7g/ml). So oil will be on the top, above vinegar. Sucrose will  precipitate (so it will be in vinegar). The question is where MSG will get to. Its approximate density is less than oil's so it will be on the top of the mixture.
So my answer is E. I have no idea how to get another way to find answer, maybe it is just knowledge test.