Confusing chemical names

xkaes · Mar 5, 2024

I have a one pound jar of photo grade Sodium Bisulfite -- that I paid for -- that I use occasionally. I also have a one pound jar of reagent grade Sodium Metabisulfite -- that I got for free -- but I've never used because I've never run across a formula that called for it.

But today, I ran across this post on another FORUM, and assume it is correct -- but I want to check.

"Sodium bisulfite as a dry chemical agent is really sodium metabisulfite. It's a common misnomer in darkroom literature. What's more confusing, some photographic chemical suppliers have both bisulfite and metabisulfite, often with different price."

Does this mean I can use my Sodium Metabisulfite without any adjustment when the formula calls for Sodium Bisulfite???

koraks · Mar 5, 2024

koraks · Mar 5, 2024

Milpool said:
If I remember correctly it is the other way around… metabisulfite you buy is mostly bisulfite.

No, the dry powder is metabisulfite. In solution, you end up with bisulfite.

xkaes · Mar 5, 2024

Milpool said:
If I remember correctly it is the other way around… metabisulfite you buy is mostly bisulfite.

Huh????

xkaes · Mar 5, 2024

koraks said:
No, the dry powder is metabisulfite. In solution, you end up with bisulfite.

Both of my jars contain white "powders" -- similar to salt or sugar in appearance.

Ian Grant · Mar 5, 2024

Analytical grade Sodium Bisulphite is unstable and expensive.

What Kodak sold as Sod'um Bisulphite is just a lower grade of Sodium Metabosulphite, a mix of both Bisulphite and Metabisulphite (70-90%). so essentially just less free SO2

Somewhere I have the JT Baker MSDS PDFs for both.

Ian

xkaes · Mar 5, 2024

Ian Grant said:
What Kodak sold as Sod'um Bisulphite is just a lower grade of Sodium Metabosulphite, a mix of both Bisulphite and Metabisulphite (70-90%). so essentially just less free SO2

So what you're saying is that my reagent grade Sodium Metabisulfite is actually Sodium Metabisulfite, but my photo grade Sodium Bisulfite is NOT really Sodium Bisulfite. It is really 70-90% Sodium Metabisulfite.

And that when a formula calls for Sodium Bisulfite, I can just ignore it and use Sodium Metabisulfite.

Seems odd/unfortunate that so many formulas specify Sodium Bisulfite, when Sodium Metabisulfite should be the term to use.

Kino · Mar 5, 2024

Gram for gram a direct equivalent?

Doesn't seem kosher...

reddesert · Mar 5, 2024

It might help to understand the meanings behind the nomenclature:
Meta- : prefix referring to dehydrated versions of a compound or ion: https://en.wikipedia.org/wiki/Meta-_(chemistry)
Bisulfite: a particular ion, HSO3- : https://en.wikipedia.org/wiki/Bisulfite
Sodium metabisulfite: a compound Na2S2O5 : https://en.wikipedia.org/wiki/Sodium_metabisulfite

When you dissolve the sodium metabisulfite in water, the ions are partially hydrogenated and you wind up with HSO3- ions. What you want is a solution of sodium and bisulfite ions, but the way to get there is to dissolve metabisulfite in water.

In general, for compounds with similar names, you might be able to use variants of different hydration prefixes: meta vs not, anhydrous vs hydrated, because we always work with solutions in water. But you typically can't substitute the suffix: sulfate, sulfite, and bisulfite are all different.

Ian Grant · Mar 5, 2024

Kino said:
Gram for gram a direct equivalent?

Doesn't seem kosher...

Well yes/no but the difference is so slight, when in contact with an alkali they both break down to the same amount of Sulphite, there will be a minimal pH difference

Here in Europe we can only buy Metabisulphite.

It is a touch confusing, Metabisulphite being pure has better preservative properties. My main use these days is in Pyrocat HD, and I add 50% extra to Part A as t increases storage stability.

Ian

Kino · Mar 5, 2024

Ian Grant said:
Well yes/no but the difference is so slight, when in contact with an alkali they both break down to the same amount of Sulphite, there will be a minimal pH difference

Here in Europe we can only buy Metabisulphite.

It is a touch confusing, Metabisulphite being pure has better preservative properties. My main use these days is in Pyrocat HD, and I add 50% extra to Part A as t increases storage stability.

Ian

Interesting, thanks.

Yet another confusing bit of knowledge to stuff in the old noggin...

Kino · Mar 5, 2024

reddesert said:
It might help to understand the meanings behind the nomenclature:
Meta- : prefix referring to dehydrated versions of a compound or ion: https://en.wikipedia.org/wiki/Meta-_(chemistry)
Bisulfite: a particular ion, HSO3- : https://en.wikipedia.org/wiki/Bisulfite
Sodium metabisulfite: a compound Na2S2O5 : https://en.wikipedia.org/wiki/Sodium_metabisulfite

When you dissolve the sodium metabisulfite in water, the ions are partially hydrogenated and you wind up with HSO3- ions. What you want is a solution of sodium and bisulfite ions, but the way to get there is to dissolve metabisulfite in water.

In general, for compounds with similar names, you might be able to use variants of different hydration prefixes: meta vs not, anhydrous vs hydrated, because we always work with solutions in water. But you typically can't substitute the suffix: sulfate, sulfite, and bisulfite are all different.

Very informative; thank you.

Kino · Mar 5, 2024

Along those lines, would you trust this bottle I picked up with some darkroom equipment?
CAS number is not quite right...

(and yes I do understand it is not Sodium Bisulfite... maybe)

koraks · Mar 5, 2024

Kino said:
CAS number is not quite right...

I see a CAT no, not a CAS no. The former stands for 'catalog' and is generally company-specific, the latter is the international identifier for chemicals (Chemical Abstracts Service).

Note that the formula given for sulfite is not quite right - should be Na2SO3. Not that it matters much.

I'd expect the bottle contains sodium sulfite. The contents seem consistent with this - then again, there's lots of granulates that look like this, but given the context, sodium sulfite is a very likely candidate.

lamerko · Mar 5, 2024

Sulfite has a very specific smell in solution with water - you can't go wrong

Kino · Mar 5, 2024

koraks said:
I see a CAT no, not a CAS no. The former stands for 'catalog' and is generally company-specific, the latter is the international identifier for chemicals (Chemical Abstracts Service).

Note that the formula given for sulfite is not quite right - should be Na2SO3. Not that it matters much.

I'd expect the bottle contains sodium sulfite. The contents seem consistent with this - then again, there's lots of granulates that look like this, but given the context, sodium sulfite is a very likely candidate.

I was speaking of the number written in green; I am very familiar with Kodak CAT #s.

The missing "2" in the CAS number for Sodium Sulfite was what was concerning me, but if you look at the "a", it almost appears as if they overwrote the "a" with a "2".

I agree, it's most likely Sodium Sulfiite, but it did give me pause.

Kino · Mar 5, 2024

lamerko said:
Sulfite has a very specific smell in solution with water - you can't go wrong

Oh yeah. Good idea. I have some known Sulfite so can do a comparison "sniff" test with a bit mixed up in water.

Thanks!

koraks · Mar 5, 2024

Kino said:
I was speaking of the number written in green

Ah, I see; that's the chemical formula. CAS numbers are digits only; the CAS no. for sodium sulfite is 7757-83-7.

I'm not too concerned about the missing '2' - think about it. NaSO3 doesn't work out if you take the valency of the ions into account: SO3 has a valence of 2-, and Na has a valence of 1+, so there must be two Na's to every NaSO3 for the salt to be stable. And since it's present as a crystalline substance (i.e. quite stable indeed - the bottle isn't filled with a hot plasma), there's little room for doubt what happened. Besides, they labeled the bottle with 'sodium sulfite' and correctly included the sulfite ion in the chemical formula.

Now, if I were to proceed with the hermeneutical analysis on this one, the only puzzling thing is the space they left between Na and SO3. Now, that one's a riddle for sure - did they doubt about the formula and anticipated adding the '2' later on, but somehow got interrupted while looking it up? Or did they have in mind to add a 'H' in order to really throw you a curve ball, as this would make it a bottle of...bisulfite. But then, we know that solid bisulfite doesn't really exist, so the plot would thicken at this point to a veritable riddle wrapped in a mystery...ah well.

It is a pretty bottle - have I mentioned that?

Kino · Mar 5, 2024

Guess it's pretty obvious I don't know a valance from a valise, but thanks for the effort!

I have several pounds more of properly labeled Sodium Sulfite, so bottle this may just remain a pretty face...

koraks · Mar 5, 2024

Kino said:
a valance from a valise

Ah, wonderful!

Doremus Scudder · Mar 6, 2024

Kino said:
Along those lines, would you trust this bottle I picked up with some darkroom equipment?
CAS number is not quite right...

(and yes I do understand it is not Sodium Bisulfite... maybe)

View attachment 364619

The bottle has likely been emptied and refilled, and appropriately re-labeled. Why would anyone go to the trouble otherwise?

Doremus

Confusing chemical names

xkaes

koraks

Moderator

koraks

Moderator

xkaes

xkaes

Ian Grant

xkaes

Kino

reddesert

Ian Grant

Kino

Kino

Kino

koraks

Moderator

lamerko

Kino

Kino

koraks

Moderator

Kino

koraks

Moderator

Doremus Scudder

Confusing chemical names

Moderator

Moderator

Moderator

Moderator

Moderator

Privacy & Transparency

Privacy & Transparency