I've just made a very small batch of chloroform/trichloromethane starting from 115 ml. of a 5% solution of NaClO and 2.3 ml. acetone. The bottom layer
of chloroform was then sucked up by a pipette and added to a small flask. To try to dry out the chloroform, I added, about five times the volume of
the chloroform, a concentrated solution of calcium chloride. Both solutions were cold. Immediately, the solution got all sort of clumpy, but not
really dense and thick. With the lid on the flask, I shook the mixture for about 30 seconds. It have rested for about 30 minutes now, to make the
product, whatever it is, settle on the bottom on the flask. The situation is as following: The top layer is a liquid flowing just like water, and
looks like a saturated solution of CaCl2 by eye. Not all clear, but almost. The bottom layer is milky white and very thick and slow flowing, almost
stiff. I really can't figure out what happened. I would appreciate if you guys would help me to find out of what I am left with.
I have tried to search it up at several chemistry pages and using Google. None of them came up with something useful.
The Kindest Regards,
Christian.Magpie - 3-5-2010 at 10:44
When you dry an organic with a salt, the salt should be anhydrous.laekkerBoy - 3-5-2010 at 10:48
Oh crap!
But thanks a lot mate! Can you tell me what I've made too?laekkerBoy - 3-5-2010 at 11:49
Yeah! I just came up with a possible solution and probably an easy way to CCl4. Please check the possibilities for this one for me. I think/hope that
it is correct and possible:
CHCl3 + 2CaCl2 + 2H2O ==> CCl4 + 3HCl + 2CaOH
But if the reaction occurs, wouldn't the following happen:
2HCl + 2CaOH ==> CaCl2 + 2H2O
and in that case start over and just catalyze the reaction to form CCl4 (Carbon tetrachloride) instead of CHCl3 (Chloroform) until no more CHCl3 is
present.
My bottom layer would then be a suspension of CCl4 and CaCl2 or CaOH if the CCl4 should happen to protect it from reacting (which I think is
impossible).
Thanks in advance.Magpie - 3-5-2010 at 12:53
Rather than speculate on whether or not your proposed procedure would work I'd rather direct you to the forum library, where you will find a published
procedure for making chloroform by an expert. Nicodem - 3-5-2010 at 13:03
I really can't figure out what happened. I would appreciate if you guys would help me to find out of what I am left with.
It depends on what the state of each phase is, but these are the names for the two possible combinations:
CHCl3(l) with aqueous CaCl2(l) is an emulsion
CHCl3(l) with CaCl2*6H2O(s) is a suspension (paste)
I'm afraid the reactions you wrote in your second post don't make any sense. The first is an impossible redox reaction, because you can not oxidise
CHCl3 with CaCl2 (there are no Ca(I) compounds such as "CaOH"). The second is a reaction with an impossible compound. Besides, why do you write
reactions if you observed no reaction? Phase changes and multiphasic systems have more to do with physics and physical chemistry. They do not
necessarily require chemical transformations, and even when they do (as for example in solvation), they are not classified as true reactions.laekkerBoy - 4-5-2010 at 06:24
Thanks a lot for your reply Nicodem. Very useful.
I would say that my mixture first started as a suspension and then, when the heavier layer settled, it turned into an emulsion.
Can this help you telling me what I've done?not_important - 4-5-2010 at 08:19
As Nicodem has implied, CHCl3 doesn't do anything chemically with CaCl2 under the conditions you had, checking on the properties and reactions of
CHCl3 in reference books or online will show that. But CHCl3 isn't the only substance in the reaction mix.
I'd say look at the reaction used to make the chloroform - the haloform reaction. Note what all the products from the reaction are. Also read
up on everything that can be in NaOCl based bleach (assuming you managed to avoid the scented, coloured, singing stuff). Magpie's suggestion is a good
one, but you may need to read further.
Once you have listed everything that is likely to be in the reaction mix, figure out how those might interact with the CaCl2 solution you added next.
laekkerBoy - 6-5-2010 at 06:36
Well, since I couldn't find out what was wrong, I discarded my chloroform.
But thank you very much everyone for your help!bbartlog - 6-5-2010 at 17:11
Chloroform and water have a small amount of mutual solubility. Either a little chloroform passed in to your (saturated?) CaCl2 solution and caused a
small amount to precipitate, or else a small amount of the salts from the haloform reaction were still in your chloroform and reacted with the CaCl2
to form a precipitate. Either way, it got trapped in the chloroform layer. You could have fixed this by distilling off the chloroform (though you
would still have had to dry it as it forms a 3% heterogenous azeotrope with water). Adding a dilute NaOH solution, shaking, and waiting for settling
might also have cleared things up.
not_important - 6-5-2010 at 17:14
If you had done as I suggested, you might have had a clue.
Haloform reaction for preformed hypochlorite
R-(C=O)-CH3 + 3 NaOCl => R-(C=O)-CCl3 + 3 NaOH
R-(C=O)-CCl3 + NaOH => RCO2Na + HCCl3
overall
R-(C=O)-CH3 + 3 NaOCl => RCO2Na + HCCl3 + 2 NaOH
Then
2 NaOH aq + CaCl2 aq => 2 NaCl aq + Ca(OH)2 ppt
which means a bunch of sparsely soluble calcium hydroxide sitting at the bottom of the container.
This is why it is a good idea to read up on reactions before you perform them, and to strive to learn the foundations of chemistry so that you can
recognise potential problems.
