opened it, used it, and not kept it in a dessicator I am guessing it is no longer completely anhydrous.
black little lumps have started to appear
Could this be oxidation to sulfate
Sulfate is white.
To know. That's exactly why I asked
I can take a picture of it, but it will hardly contribute to anything. But I stopped ordering from there - it really seems that there are some atypical impurities
If your Sodium Sulphite is monohydrated you'd need 1.14x as much weight for the same molarity, with crystalline it works out roughly twice as much.
Has anyone tried to dry out chemistry by using a small, hand held vacuum pump
Quite sure, it's going back to my school days as I mainly work with organics but hardly difficult stuff.Are you sure you're not confusing sodium sulfite with sodium carbonate here? To avoid confusion, can you give the CAS# for each of the hydrates you mention?
I don't normally use CAS numbers
In each case adding a molecule of water of crystallisation will add 18 to the molecular weight
The reason I'm asking is if sodium sulfite monohydrate is an existent, practically traded compound, it'll have a CAS number. I tried to find it, but can't.
It does have a PubChem entry: https://pubchem.ncbi.nlm.nih.gov/compound/Sodium-sulphite-monohydrate But I wonder if that's perhaps auto-generated.
If you search for "sodium sulfite monohydrate" on e.g. Google, you'll find about a handful of references, none of which seem to give any firm evidence that the compound really exists, or under what conditions. You may find this thread informative on this point as well: https://www.photrio.com/forum/threads/clarifying-measurements.43168/ Here, the well-respected Photo Engineer brings up sodium sulfite monohydrate, after which some discussion ensues that boils down it not being practically relevant.
Given the instability of sodium sulfite heptahydrate, this is not a common trade item (it may be traded in minor quantities for analytical purposes, IDK), so it's unlikely any photographic formula to call for it, nor is it likely that you inadvertently end up with a jar of it under the impression of having bought plain old sodium sulfite (anhydrous).
The term 'crystalline' I see used in conjunction with sodium carbonate, referring to the decahydrate. In the context of sodium sulfite, I wonder what it is supposed to mean.
Yes, I understand how hydration works in terms of molecular weight. My point is really about the practical context. At a theoretical level, it's easy enough to argue that hydration matters and that conversions/substitutions are possible. But I think the first question to ask should be: " is there a problem?" I don't think there is.
When a photographic formula calls for sulfite, I don't think there's any reason to worry about species/hydration, for the simple reason that everything (what the formula calls for, and what your favorite seller offers) will be anhydrous.
I have seen crystalline used in photographic books for quite a few reagents.
Why would all this have to be made so damn complicated? It's totally unnecessary!
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