Demystifying the White Powder

An update on the ‘mysterious white powder’ of my last post. It was the subject of some interest in the department today and we resolved to identify it.

Some crude analysis of the powder: it fizzes when you add it to a solution of HCl – almost certainly a carbonate of some sort.

The pH of the powder dissolved in water was done independently twice (I did it and then my lab mate did it not knowing I had already done it!) and we both got a pH of 11-12 – consistent (see this table) with either sodium carbonate or potassium carbonate (not bicarbonate, which would be more like a pH of 8-9).

I jokingly suggested that we should do a flame test on it next. Well, it turned out we have the capacity to do so and it was determined quite conclusively that it was in fact sodium carbonate. Debate rages on whether it is the anhydrous form or a decahydrate.

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6 comments on “Demystifying the White Powder

  1. Moises says:

    Much time has passed since my last flame test but I think that the picture is wrong. Sodium is yellow in flame test right? :S

    • David Perrey says:

      I put that in to be a pretty picture at the bottom, but you are right, it was certainly yellow when we were doing it today! (and Wikipedia agrees)

      Changing picture (for those who read this later).

  2. [...] at Chemical Space, a mysterious white powder cushioning trimethylsilyl cyanide turned out to be sodium carbonate, and I’m with David in wondering why the company didn’t identify the chemical anywhere [...]

  3. Excellent ! Higher the chemistry Learning !

  4. milkshake says:

    its definitely not decahydrate, decahydrate is ice-like, chunky and quite soft (similar in appearance to sodium sulfate decahydrate). But it could still be some lower hydrate, (n = 1-2). Sodium carbonate decahydrate on dry air loses some water and crumbles into powder but I don’t believe it gets completely anhydrous

    • David Perrey says:

      I may have overstated the intensity of the debate over the hydrate, though I am grateful you took the time to post that it can’t be the decahydrate. I’d guess that there might be a couple of water molecules involved, but not much more than that. In fact, you’d probably want minimal water involved with a bottle of TMS-cyanide to prevent generation of HCN in the first place.

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