A Small Work-up

[Xylene]

This Post is mostly a study of Lab technique for the new folks. I'm using formal chemical apparatus in these pics, but you don't really need anything so elaborate. In another thread I read an inquiry about "clay triangles" and their use...so I decided to use one here to support an evaporating dish over an alcohol lamp. On a budget, any means of boiling a pyrex beaker would do as well.

However, the Clay Triangle IS the approved method of supporting a red-hot crucible over a Bunsen flame. In this application the ceramic bars of the clay triangle should support the tapered crucible about 1/3 of the way up its side. So then you must buy the correct size Triangle to fit your Crucible.

In this Post I will be refining chemically pure Cobalt Sulphate Co SO4 out of VERY impure cobalt carbonate and battery acid (approx. 25% H2 SO4) http://en.wikipedia.org/wiki/Cobalt_sulfate A Lab purification is generally called the "work up"

This is the "3 inch" size of clay triangle that just fits within a standard "4 inch" iron ring that I will use to support a small evaporation dish.

[Xylene]

So then, I added about 120 ml of battery acid into a 500 ml beaker and very slowly stirred in small amounts of crude cobalt carbonate. Go slow as it of course foams up as the CO2 leaves. When further additions produced very little bubbling I decided the mixture was near neutralized, and added a few ml of acid more. (The very crude nature of these starting chemicals are not worthy of calculations)

I heated the beaker upon a hot plate until slow boil. This should also drive out the remaining CO2. The liquid appeared very dirty and dark, not the brick red I would expect of a cobalt sulphate solution. First I did a hot filtration with a coarse "Fast" filter paper and got the VERY black impurities to the left side of this pic. I expect this black was mostly cobalt oxide.

The filtrate was still not as clear as I would like, so I did a second hot filtration using a very fine filter "Slow" paper. The right side of pic shows even more fine black particles were removed. The trick with filter paper is to remove an acceptable amount of solids...without plugging up and stopping the drain of liquid. Hence the range of filter grades available. Many home chemists simply use good coffee-filters.

[Xylene]

Ok now to transfer the filtered solution to a small evaporating dish and gently heat it. It should be hot enough to show vapor leaving but not so hot that it bubbles and splatters material out of the dish.
I evaporated off enough water until I saw a faint trace of a "crust" appear at the surface sides of the liquid. Then I capped the alcohol lamp and allowed the liquid to cool down to room temperature.

[Xylene]

Pouring along a glass rod is a useful skill. Mostly this prevents the liquid from running down the outside of the container as you pour. (Note that most tea-pots will NOT pour without dribbling down the pot onto the table lol) Also pouring along a rod allows you to control the direction and flow of the liquid during hot filtrations as simply "dumping it in" may puncture the wet filter paper at the tip of the paper cone. Therefore, direct your pouring against the sides of the filter cone, not into its apex.


To pour along a glass rod you must first wet the "down end" of the rod so the liquid will flow along it. Next I have saddled the rod into the notch of the dish pouring lip like this (so I can pour one-handed).
This technique is most common when pouring from a beaker, except one hand holds the beaker while the other hand holds the rod against the spout.

[Xylene]

Now we have the liquid (called the "mother liquor") we poured off in the left dish...
And the crude product cobalt sulphate in the right dish.
Next I dissolved the crude product in just enough boiling water to absorb it completely into solution. As this solution cooled slowly to room temperature, a slight crust of impurities formed on its surface. I skimmed these off with a small silicone rubber spatula from a Kitchen Supply store. (silicone rubber can take more than 400 F. and resists most chemicals. The cheap plastic or regular rubber spatulas will not work)

[Xylene]

Here on the LEFT is the decanted mother liquor containing considerable impurities.

At the MIDDLE is the crude product after mother liquor was removed. This was dissolved in just enough hot water, and allowed to cool for a second crystallization. The impure crust was skimmed off as described. After skimming and cooling, again decant off the liquid to find the crystals on the bottom of the dish. ( This will produce acceptable purity.)

At the RIGHT are the pure crystals of Co SO4 recovered from the recrystallized crude product. These crystals were gently washed with acetone from the wash bottle (middle background)

[Xylene]

And here we have high purity crystals! Beautiful deep carrot-red feathers...crystals some what in the shape of the blade on a French Chef's Knife (that detail is hard to see in these small pics).
I hope this silly Post of mine has been helpful to the new basement chemists. Remember you do not need such professional equipment to get started. An alcohol lamp, a pyrex custard-dish, a plastic funnel, 3 test-tubes and a clamp will start you off.