[mikachu]

Hello all!

I did an experiment in the lab today which was titled "The Independence of an ionic reaction from a counter ion" (I hope this makes sense, I translated it from German).  I'm having a lot of trouble formulating the chemical equations and understanding the importance of this experiment.

Experiment 1:
1.  Add 1ml of CHCl₃ with one patty of solid NaOH to 1ml of distilled water.
2.  Heat for about 1min.
3.  Let cool, then add enough 2N HNO₃ until the test tube is half way filled.
4.  Mix well.
5.  To this you now add a few drops of AgNO₃ solution.

Experiment 2:
Repeat experiment 1, but add distilled water instead of HNO₃.

Experiment 1 produces a white fallout (AgCl)
Experimnet 2 produces first a black fallout (AgOH) and then a brown fallout (Ag₂O)

So far I've got:

CHCl₃ + NaOH    NaCl + CCl₂ + H₂O

but I have no idea how to proceed or why the HNO₃ is necessary 

I guess next I would have to add HNO₃ into the equation, but how do I predict the products and how do I end up getting AgCl?
Also does the heat play a role other than dissovling the NaOH faster?

Any help would be much appreciated! Thanks!

[Archer]

I am not sure that this reaction goes as far as the dichlorocarbene.

 CHCl₃ + NaOH  NaCl + :CCl₂ + H₂O

The :CCl₂ is extremely reactive and doesn't hang around for long, their chemistry is a bit advanced for high school.

It might be that the CHCl₃ is just deprotonated to (CCl₃)^- Na⁺.

[Archer]

I am not sure that this reaction goes as far as the dichlorocarbene.

 CHCl₃ + NaOH  NaCl + :CCl₂ + H₂O

The :CCl₂ is extremely reactive and doesn't hang around for long, their chemistry is a bit advanced for high school.

It might be that the CHCl₃ is just deprotonated to (CCl₃)^- Na⁺.

Upon thinking about this I am not so sure about this reaction. I think perhaps the chloroform is hydrolysed to sodium formate in the first step.

[magician4]

@ archer:

I am not sure that this reaction goes as far as the dichlorocarbene.

IMHO, this is the classical approach to dichlorcarbene (under PTC-conditions, if memory serves), and still is in use in labs today, and that's why the experiment as described worries me a bit...
... as - if my imagination of "boiling ..." was true- the test tube should have contained dichlorcarbene, which, upon contact with oxygen/air, will form phosgene instantaneously, which is kind of voilatile (at least the fraction that is not subsequently hydrolyzed to carbonate, i.e. can escape before hydrolysis)...

to boil stiff NaOH , aq. with CHCl₃  bad, bad idea


@ all:


asides from this, there are many alternative, much safer ways to produce chloride as product of a nucleophilic reaction (t. butylchloride / NaOH aq. comes to mind), and I don't see the point in doing it in a way as reported, i.e with a very very veeeeery poisenous gas as byproduct, just for the trivial purpose of having chloride around...

last not least, the whole title question seems kind of unrelated / contradicting to the experiment, as this experiment shows the dependency of a ionic reaction (i.e. formation of either AgCl or AgOH / Ag₂O , depending on OH^- or Cl^- running the show) , and not the independency instead.


might this be an error in translation ?


regards

Ingo