1. Why does CH 2 Cl 2 solvent (lower layer) have higher density than water while

Question

1. Why does CH2Cl2 solvent (lower layer) have higher density than water while non-chlorinated solvents like hexanes and ether (top layer) have lower density than water, i.e. what exactly is it about Cl that causes this difference?

2. Assuming the following values, calculate how much caffeine should be obtained (the "Background Theory" file shows how to perform this calculation): Kp (CH2Cl2/water) = 3.0; 20 mL for the water layer with 25 mg of caffeine in it before extraction and 2 x 6 mL for the CH2Cl2 layers.  

3. Explain how your acid-base solubility results conclusively identified your unknown compounds. Which two of the five compounds would be soluble in dichloromethane solvent (and why not the others)?

Explanation / Answer

1)for starters, one atom of Cl weighs the same as two molecules of water. Cl is certainly heavier.

But that alone wont do. Methane is a gas and is considerably less dense than water. Consider CH3Cl. It is heavier (molar mass) than water, has one Cl atom yet is less dense than water. On the contrary, H2O < CH2Cl2 < CHCl3 < CCl4 (increasing order of density)

So, it probably makes sense when you have some 'heavy atoms' in the molecule. And in this case, for our liking, the entire molecule happens to be compact too

2)

k = cI/cII = mI /VI /(mII/ VII) = mI *vII /(mII *VI)

Your 25 mg is first in 20 ml water, after first extraction its distribute 1:3 in methylen chloride

3) benzoic acid,cinchonidine (free base)

benzoic acid and cinchonidine(free base) soluble in dichloromethane solvent, but sodium benzoate, glycine, and cinhonidine2H+ are not because

Dichloromethane, or DCM, is fairly non-polar solvent, so it will dissolve most organic compounds with ease. It cannot, however, dissolve charged compounds very well. It isn't polar enough and it can't hydrogen bond, which severely limits its ability to solubilize salts and other ions.

Benzoic acid and the free base form of cinchonidine, however, are neutral and relatively nonpolar and will dissolve in DCM. Benzoate is negatively charged, glycine contains both positively- and negatively-charged groups, and cinchonidine-2H+ obviously has a 2+ charge. As a result, none of these species will dissolve in DCM very well

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