Lab..again

Question

0.050g benzoic acid/succinic acid/sodium benzoate.

-choose 1 and put 0.050g of that compound into 5ml conical vial

-add 2ml methylene chloride and 2ml water

-cap vial and shake until all solid is dissolved.

-let solution sit until 2 layers are formed (no clear emulsion)

-separate the bottom organic layer with a pasteur pipette to another dry conical vial [I used a centrifuge tube]

-add sodium sulfate(drying agent) to dry out the sample

-wait untill solution is clear or at least for 15 min so the water can be absorbed by the drying agent.

-pipette out the organic layer leaving behind the solid. Pipette the layer into a preweighed conical vial

-evaporate the organic layer in a hotwater bath and weigh vial after cooling to determine the ammount of compound in the organic layer.

Problem:
Both Sodium Benzoate(one I worked with on my own) and Succinic acid (other person worked on that) after heating and such did not produce a increase in the mass of the vial they were stored in. I personally for the Sodium Benzoate had a brown stain on the bottom of the conical vial but when it was weighed it weighed exactly the same as before the experiment. I know there wasn't anything at the bottom of the vial before the the experiment since I am meticulous at washing the glassware (something I learned in analytical chem) and I made sure that there wasn't anything in there before.

I was told that the mass of the compound in the vial could be so small it's negligible (vial weighed 22.117g before and after). The the vial of the other student didn't have anything in it but was supposed to have succininc acid compound in it but it came up empty in the end.

The reason I post all this is b/c I have to come up with a reason for why this happened to put in my lab book.
The other people in the lab who did the same compounds also came up empty handed so to speak with the Succinic acid and sodium benzoate.

~my thoughts on this are that since the compound was mostly still in the aqueous layer could it be that the compounds of succinic acid and sodium benzoate are more water soluble than they are methylene chloride soluble?

Thanks alot =D

Answer 1

That would be my guess. 1 g succinic acid dissolves in 13 mL water and is practically insoluble in pet ether, CCl4, somewhat soluble in acetone, etc.
Sodium benzoate, of course, is a highly polar compound and is VERY soluble in water.

Answer 2

Thanks Dr.Bob, I was thinking that but I didn't have any other guesses except maybe not shaking enough but the first guess was a better one.

Thanks again Dr.Bob =D