nannah - 19-11-2014 at 14:21
Hi, guys. I have thought about start purifying OTC chemicals, like baking soda, and separating paint thinner, if i will ever get some free time to
actually do it.
What i wonder is what ways there are to check to see if it could be called "reagent grade", and if it anhydrous, etc.
Thanks in advance. /N.
aga - 19-11-2014 at 14:32
GC/MS. Can't beat it.
Metacelsus - 19-11-2014 at 16:00
That won't work for non-volatile compounds like sodium bicarbonate. For inorganic stuff X-ray diffraction is great.
confused - 19-11-2014 at 16:53
HPLC for soluble non volatile compounds
Edit: i think he means ways for someone without all that fancy equipment to test for impurities
[Edited on 20-11-2014 by confused]
Dr.Bob - 19-11-2014 at 16:57
It is dependent on what type of compound it is. For inorganics, it is not simple to test, but simpler to just recrystallize or keep purifying until
you get the results in a known prep or purification. For liquids, a BP is helpful and easy to get. For organic solids, mps are useful. X-ray
diffraction may be great, but it does not quality for OTC or homemade, unless you are Sheldon Cooper. Same for CG unless you are Sean Connery.
Metacelsus - 19-11-2014 at 18:39
Okay, I'll be realistic (I was being somewhat of a troll previously).
Test the compound with some of its known reactions (for example, if you think you have potassium iodide, try adding sulfuric acid and see if iodine
forms). This is a good way for qualitative identification of compounds. On the quantitative side, titration is a good idea, and is pretty easy for
most things (acids, bases, oxidizing and reducing agents, etc.).
Also, as a general rule, if something forms nice, large crystals, it's usually a pure compound.
m1tanker78 - 19-11-2014 at 21:19
I can't walk the aisles of the grocery/hardware stores without thinking, "Hmm, I can use X product to make Y reagent. Many OTC chems are surprisingly
pure. Some can be tested and purified relatively easily by exploiting solubility, for example.
Tank
woelen - 20-11-2014 at 00:38
A good way to assess the purity of the compounds is testing for (non-)presence of common or expected impurities. The nature of these impurities is
specific for each compound. Some examples:
I made KIO3 from KI by means of electrolysis. A common impurity in KIO3 is iodide ion, I(-). I tested by dissolving some KIO3 in dilute H2SO4. The
liquid remained colorless. This means that the KIO3 does not contain any reducing impurity, hence no I(-), nor Br(-) and Cl(-), as all of these would
cause formation of iodine when dilute acid is added. As a control experiment I added a single tiny crystal of KI and immediately I obtained a brown
liquid.
I also did a test with pH indicator, in order to assess presence of hydroxide ion or carbonate ion, which also is fairly common in KIO3, especially if
it is made by means of electrolysis (pH tends to go high during electrolysis). My KIO3 only is very weakly basic.
I purchased technical grade NiSO4.xH2O. This stuff was dirty green with brown stuff in it. Solutions were turbid. I dissolved all of it in water,
filtered and then allowed 90% or so of the liquid to evaporate. Crystals of bright green hydrated nickel sulfate settled at the bottom. I rinsed the
remaining liquid from the crystals and dried the crystal mass. This has given me quite some pure nickel(II) sulfate. Testing was done as follows:
- Dissolve some in water: Solution is totally clear and light green.
- Add a drop of solution of AgNO3 to the clear solution. No cloudiness is observed, so it is free of halide ion and it also is not alkaline.
- I prepared a fairly concentrated solution of the nickel sulfate and added a drop of this to 5% household ammonia: I obtained a clear purplish/blue
solution, due to formation of nickel(II) ammine complex, but the liquid remained clear. This means that (nearly) no iron is present in the solution.
Iron forms no complex with ammonia and precipitates as hydroxide.
- I prepared a dilute solution of the nickel sulfate, added some sulphuric acid and sodium peroxodisulfate. I added a single tiny drop of AgNO3: Faint
pinkish coloration of the solution. This means that a tiny amount of manganese is in the nickel sulfate. Manganese is oxidized to permanganate by the
peroxodisulfate solution. Given the extremely strong color of permanganate, it can be concluded that the amount of manganese must be very low, most
likely less than 0.1%.
- I also would like to test for copper(II), but I do not know an easy test which detects copper(II) unambiguously in the presence of a lot of
nickel(II).
In practical experimenting, my nickel(II) sulfate is perfectly fine.
In this way, I do not assess absolute purity, but I assess the absence of certain disturbing impurities. In many cases, only certain impurities are a
problem. E.g. if my NiSO4 also would contain a small amount of K(+) ions or Na(+) ions, then I would not notice and experiments would not be affected.
Presence of e.g. ClO(-) ions in it would almost certainly disturb many experiments.