binaryclock - 2-5-2013 at 22:00
Hello:
I've recently created a batch of crystals of NaCLO3 that were in electrolysis cells for three days in a solution of NaCl.
After three days, I boiled the solution to remove any hypochlorates and then added the same amount of KCl to the mixture and allowed it to perform
metathesis. Some crystals formed immediately and sank to the bottom. After a while I took the solution and put it in the freezer to about 0c. At
0c, almost half the beaker was filled with crystals so I harvested them by decanting the liquid solution and putting the crystals on filter paper to
dry.
Once dry, when burned the flame was yellow/red. It was not purple like my KCl syth crystals. It seems that I have more NaCLO3 than KCLO3 in my yield
from the NaCl cell. What did I do wrong here?
Now that I have about 40g in dry crystals, how should I best go about getting them converted to KClO3 crystals?
Thanks
chemcam - 2-5-2013 at 22:14
Even a small amount of NaClO3 contamination will discolor the flame of KClO3 you most likely have more K than Na so I would take advantage of their
different solubilites and do a 0C water wash. You will lose some product but gain purity.
binaryclock - 2-5-2013 at 22:23
Thanks for your reply. I'll try that tomorrow and see how it goes. I wasn't aware that a small amount of NaCLO3 discoloured the flame.. thanks for
the info!
ScienceSquirrel - 3-5-2013 at 03:27
Sodium floods everything in flame tests, your product could be at 99% pure and the sodium would still show up.
http://chemistry.about.com/od/analyticalchemistry/a/flametes...
binaryclock - 3-5-2013 at 05:26
Cool thanks for the link. Scumbag sodium 
hyfalcon - 3-5-2013 at 06:51
That's why many of us start with KCl when we want the end product for use in pyrotechnics. If the sodium is never there then it can't ruin the show!
phlogiston - 3-5-2013 at 07:17
Fortunately, the solubilities of KClO3 and NaClO3 work in your favor:
1. good recovery
KClO3 solubility varies strongly with temperature and it is only moderately soluble in cold water, so the recovery of recrystallizations is quite
good.
2. Big difference beteen solubility of NaClO3 and KClO3
NaClO3 is -very- soluble, even at low temperatures, so it is doable to get rid of even small impurities of NaClO3. For best results, use suction on
filtration (buchner filter works very well) to remove recrystallisation liquor and wash once/twice with ice-cold water in the filter.
blogfast25 - 3-5-2013 at 08:21
There's a thread on converting NaClO3 (used to be in some weed killers) to KClO3 on this forum.
Fantasma4500 - 3-5-2013 at 15:11
i would say even just using cloth for filtration and then squeezing it would be enough, a neat little tip is to take tissue paper, fold filter in half
and suck the water out of both the insoluble and the filter with the dry tissue paper
this can be done with normal filter paper ofc.. very very handy especially if you can combine that with ether then you could do it in literally less
than 10 mins
in short
squeeze out the liquid of the filter, or scrape the crystals onto tissue paper and let them dry, then you shouldnt need to purify it further by
recrystallization