Dichromate Salt separation problem!
Greetings! Happy New Year, everyone. 
I have got a slight problem of separating potassium dichromate from initially a mixture of potassium dichromate and sodium chloride.
Last week, I dissolved about 500g (2 mol equivalent) of sodium dichromate in some hot water to form a saturated solution.
I then dissolved 4 mol of potassium chloride in some hot water in a separate beaker and added this potassium chloride solution to the saturated sodium
dichromate solution, aiming to produce my product potassium dichromate.
Upon addition, the large amount of fine orange precipitate instantly clogged the stirring and I had to add about an additional 350ml of water to keep
the magnetic stirring going.
Upon the extra water addition, all solids dissolved and formed a deep orange red solution.
At this point, I decided to boil off some of the water and try to precipitate out the potassium dichromate by making use of the solubility differences
of potassium dichromate and sodium chloride at boiling solution temperatures.
and here comes the problem...
After some boiling, I decided to cool down the solution to precipitate out the product potassium dichromate. As the solution reaches room temperature,
quite a lot of orange solids precipitated out.
I decanted off the residual liquid and continued the boiling. (I also dried the crystals obtained under a 'steam water bath').
It is at this point that I realised that there is a very very fine brownish red precipitate that not even filter paper could filter this out in the
filtrate.
In fact, before filtering this suspension, I actually added quite a bit of water to the solution containing this fine precipitate to try to dissolve
this precipitate as I thought this might be a very fine suspension of fine dichromate crystals. (Which the precipitate turned out to be some stubborn
insoluble compound that did not dissolve upon addition of quite a bit of water).
After this mess, I decided to bring out my fritted funnel to filter off this suspension. This worked and I was left with a clear orange solution.
...Which I should have used my fritted funnel in the first place because the gravity filtering took ages... To be honest I don't really know why I didn't in the first place, it might have been because I was busy doing other
things and I wasn't in a hurry in producing the potassium dichromate which I now am!!
I then repeated this boiling off and filtering step until I obtained quite a bit of the orange solid.
I weighed the solids I obtained and realised I have actually got a 140% yield of potassium dichromate from starting sodium dichromate...
I have been fooled by the strong colouration of the dichromate that 'dyed' the sodium chloride salt that also precipitated out...
Now what?
I am left with a generous amount of dry orangey solid...
Does anyone know how to separate potassium dichromate that I intend to get from this mixture of potassium dichromate, sodium dichromate, potassium
chloride and sodium chloride?
Please can anyone give me some suggestion because this massive pile of orange mess containing this chrome(VI) carcinogenic compound has been sitting
around for a while and I really want to finish this off!
Thank you in advance!
P.S: I intend to use this potassium dichromate for some alcohol oxidation.
I am aware that sodium dichomate works well for this and there is no need to convert the sodium dichromate to potassium dichromate...
But here's the thing... The container that the sodium dichromate came in wasn't sealed properly and the highly hygroscopic property of sodium
dichromate can explain the rest... and this is why I think converting it to potassium dichromate might make my next projects cleaner and easier to
handle with... Never thought this simple double displacement reaction can be this messy and time consuming!
I also have some sulfite around for last resort to reduce the chrome(VI) to chrome(III)... but this will be my last resort because I don't want to
waste this valuable dichromate...
Thank you again!
[Edited on 8-1-2016 by dawsonsuen]
Long story short, Chem is try!
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