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Author: Subject: measuring the purity of my home made sodium chlorate and how to improve purity
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[*] posted on 18-4-2015 at 22:20
measuring the purity of my home made sodium chlorate and how to improve purity

I made some sodium chlorate that I want to convert to perchlorate for rockets.

I want to test its purity, so I decided to use the decomposition method.
I followed this lab, except I'm using NaClO3 instead of KClO3. So I made sure to gently heat it to drive off the water.

I used a 15ml stainless steel crucible which could be a mistake since it gets attacked by the molten salt, but very little since the weight changed by only 0.01g. I'm using a propane blow torch.

The 1st time, I added too much chlorate (~8g) and a bit got lost from sputtering or started foaming and overflowing the crucible.

After trying again with 2g, I made these measurements:

Mcrucible = 8.76g
Mcrucible + ClO3 + Cl + H2O = 10.38
Mcrucible + ClO3 + Cl = 10.37
Mcrucible + Cl = 9.78

These data say that 18.7% of my chlorate mixture is NaCl, which is a lot higher than I'm expecting. I'm a little doubtful if all the chlorate has decomposed. I've heated it for ~15 minutes.

Even for my 1st attempt that I scratched out, I calculated a similar percentage.

Also, I'm assuming the initial mixture is either ClO3 or Cl, and that only NaCl remains after heating. Are these assumptions correct?

Although I don't care too much about the impurity since it's only an intermediate product for eventual conversion to ClO4, I would like to make it better if it's not difficult.

The way I harvest the ClO3 is by just scooping the crystals at the bottom of the cell. I do this when the cell is warm at ~60C. Then I just top off the cell with a saturated NaCl solution. I usually don't further purify the harvested crystals unless they look dirty.

It seems I could increase purity by harvesting when it's cold? Based on this mutual solubility diagram,

Attachment: NaClO3_NaCl_mutual_solubility.svg (92kB)
This file has been downloaded 540 times

if the system is all liquid and has 10% NaCl at 60C, then it's in on the line of NaCl saturation and any loss of water from electrolysis will cause only NaCl to precipitate out (assuming the electrolysis doesn't convert any Cl to ClO3). But if the system was at 20C and also 10% NaCl, it would not be saturated with NaCl and the loss of water from electrolysis will only precipitate ClO3.

So it seems I should not allow any crystals to form when the cell is running hot? The moment I see crystals forming when hot, I should stop the electrolysis, let the cell cool and the collect the crystals. Do I have the right idea?

[Edited on 19-4-2015 by UncleJoe1985]
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[*] posted on 19-4-2015 at 14:53

Titrate for Chloride.
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[*] posted on 19-4-2015 at 15:06

Can't you precipitate the crystals from the solution by adding an amount of 2 - Propanol? I think I saw that somewhere...
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