During the lab, my TA (Teacher Assistant - the one who supervises the lab) kept saying that if you mix this with this, it will be immisible so two phases will be formed: aqueous and organic. The problem is with a seperation funnel which will eventually have two phases, A and B and we have to identify which one is aqueous and which one is organic.
How did he know so easily just by looking at it? He sometimes added water aswell to see if they seperate or not (which I have no idea what that means.)
If you have a separatory funnel with two layers, and you add water, one of the two layers will get bigger - that is the aqueous layer. Another way to distinguish the two is to take a small vial or test tube full of water and add a few drops of each layer to the center of the water with a pipette. If you are adding the organic layer, cohesive drops will come out of the pipette and either rise to the surface or drop to the bottom of the vial (depending on the density of the organic solvent). If you are adding the aqueous layer, it will mix with the water in the vial and you will not see cohesive drops in the water.
EDIT: In case it helps explaining my question, here's the class question:
"A students adds the following to a separatory funnel: 30 mL of water, 100 mL diethylether, 15 mL 0.1 M HCl, 0.25 g cholesterol and 0.25 g tyrosine, and proceeds to shake the funnel. Indicate the contents of phase A and phase B."
In this case, it's easy to pick out the solvents - they are the ones in the largest amounts. (Your 0.1 M HCl solution is a solution in water so it will be part of the water layer).
Inorganic salts, acids, and bases are almost never soluble in organic solvents. If they are soluble at all, they will be soluble in the water layer.
It takes some experience and some understanding of the structure of your molecules to determine which layers the organic components will be in. In your case, you want to know whether the cholesterol and tyrosine would dissolve best in ether or in a dilute acid. Cholesterol is a large carbohydrate with almost no polarity - the hydrophilic OH group is very small compared to the hydrophobic rest of the molecule. It could be ionized in a strong base which would give it a negative charge and make it more polar, but since you have an acidic solution, it will not be. It will most likely dissolve in the ether.
Tyrosine is an amino acid (has both an -NH2
and a carboxylic acid attached to the same carbon) that also contains a phenolic hydroxy group. All three of those functional groups are polar and hydrophilic, while only the benzene ring of the phenol is hydrophobic. In addition, in dilute acid, the amine is protonated (-NH3+
), making it even more polar. This compound will most likely dissolve in the water layer. If you had a basic solution instead, the amine wouldn't be protonated and the carboxylic acid would be deprotonated, and if the base was strong enough, the phenol would be deprotonated as well. Even at neutral pH, the carboxylic acid would be deprotonated and the amine protonated to give a zwitterion. All of these variations are very polar, and amino acids are almost always water soluble at any pH.