posted by ~christina~ on .
What would the best way to determine the organic layer from the aqueous layer in a extraction procedure?
~would it be to add a few drops of water to each layer and see what happens? or is there a better way since this procedure of adding a few drops of water to the extraction vial would introduce water into the organic layer and then the water would thus have to be removed and thus would defeat the whole purpose of seperating the layers in the first place.
The easiest way is to look up the densities of the organic layer and water. But you already know the density of water as 1.00 (at least close enough). The organic layer will be on top if it is less dense and on bottom if it is more dense.
The reason I ask is b/c the book says to not necessarily trust the book b/c If you have another compound dissolved in it which makes it denser than the water it can go on the bottom or be reversed.
I can actually look up the info but the density of the compounds aren't in the Merck Index (or I can't find them)(I bought it new 14th edition and it came with a cd too).
saturated aqueous sodium bromide
the last 3 are just to let us determine which is a organic layer when mixed with water, I also have to determine which is the organic layer when the 2 last ones are mixed too.
I have to make the table of chemicals in my lab book before lab and I looked at the Merck Index but either it wasn't in there or I don't know how to read the notation but I'm thinking it's the latter.
If they are in a sep funnel, you have no choice except to pull the bottom layer off first, then the top layer next. After they are in two separate containers, adding some organic solvent to both will tell you (using organic solvent instead of water gets around the objection in the original question), the odor should tell you, etc.
Um I have to use a pasteur pipette to get the bottom layer off from the solution in the conical vial.
I guess I could add some after seperating them since the instructions are to evaporate the solvent anyways.
That's a good I idea to add the organic solvent instead of water to the individual separated solutions.
Thanks Dr.Bob =D
From The Merck Index---
methylene chloride density = 1.33 g/cc
n-butyl chloride = 0.89 g/cc
n-butyl bromide = 1.27 g/cc
so I expect you are reading it. Were they not listed. Go to the index FIRST (don't try to look them up by name in the alphabetical listing because they may be known by several name) since the index will list them several ways and they are crossreferenced so if you look up dichloromethane it will say "see #??" and go to that number and it is listed as methylene chloride.
An aqueous solution of NaBr COULD be as dense as n-butyl bromide but my gut feelihng is it ins't. Anyway, you will have n-butyl bromide there and you will have the saturated solution of NaBr there, so in a small test tube, add the two and see which floats.
for methylene chloride...
it was listed as
but here was a d-4-0 before this and after this there was a d-4-20 and a d-4-30 and after that there was something noted as n-D-20...
Which should I use ?? the one listed as d-4-15 all the time?
(I'll analyze the rest after I go and eat so I'm not done with this but I wanted to go and list what I saw for the methylene chloride first)
the nD20 is the refractive index at 20o. The n is refractive index, the D is using the D lines of sodium (spectroscopic lines of 589.0 nm and 589.6 nm) for the light source and 20 is T.
d is density. The notation of d420 = xx means the density of the substance at 20o C referred to water at 4o C.
The other values of density, all referred to water at 4 C are values for different temperatures C. I would use 20 or 25 if those are listed since those are closest to room T but 15 or 30 are just below and just above. 15 C is 59 F (a little cold for room T) and 30 C is 86 F (a little warm for room T). 20 C is 68 F and 25 C is 77 F and those are reasonable numbers to use. What to do if 20 or 25 aren't listed? I use whatever is there because let's face it, density won't change that much from 15 C to 20 C so if there is a number there for 15 and that's the only number listed, use it UNLESS you are REALLY trying to determine the density to four or five significant figures for a reference manual OR you have a pot of gold at the end of the rainbow that's yours if you get the right answer.
Pertaining to looking at the index first: I'm being overwhelmed by all the different compounds with names I don't even get...=(
Oo..I guess I'm supposed to know that D is using the D lines of sodium ?
~I'm getting to learn things 1 thing at at a time. =)
so n is the refractive index...now I know another thing..
I really didn't see any cross references saying "see #" ..maybe it's not like that in the new edition?
n-butyl chloride = 0.89 g/cc
~I found it was this at 15 C in the bk
Okay So I know know to use the 20 or 25 C or 15 if those aren't available for the density.
XD .."pot of gold"...I'd think I'd have to figure out how to use the Merck Index before I think about that Dr.Bob..
"An aqueous solution of NaBr COULD be as dense as n-butyl bromide but my gut feelihng is it ins't. Anyway, you will have n-butyl bromide there and you will have the saturated solution of NaBr there, so in a small test tube, add the two and see which floats."
So if it's less dense then I could assume it's the upper layer..and then test out the hypothesis right?
However they will be added already in a tube for us and we have to deturmine which is which in the mix =(
The book says to separate the layers and then go and drop some water and see which of the 2 layers increases in volume after the addition of the water.
This I think would work fine except for the other lab with the actual sample where we have to extract the compound from the aqueous layer and separate the 2 layers.
But I think that your response earlier that I could use the organic solvent instead of the water to be a good idea contrary to the books advice of using water which wouldn't make any sense if I had to go and separate out that water droplet later.
Thanks alot Dr.Bob =D
(I wouldn't know where to get the info on which temp to use for the density in the book anywhere else)
Yes, your edition is cross referenced, it just isn't obvious. Look up dichloromethane in the index. In my edition, it says see #xxxx. When I look at that number, it shows methylene chloride which is just another name for dichloromethane. The idea is they don't want to list the compound in two places so they put it one place and make two entries (or more if more is required) in the index.
Hm..so it is!
Thanks for clarifying that Dr.Bob =D
(I thought you were refering to the actual description of the compound where they say "see #" not the index)