Importance of anyhydrous sodium sulfite being water-free

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khennessy

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In using anhydrous sodium sulfite in a developer formation how important is it that it is totally dry. I have the chemical but having opened it, used it, and not kept it in a dessicator I am guessing it is no longer completely anhydrous.

Would I need to dry the sodium sulfite at 100 °C or would that cause damage to the chemical? Or could I calculate the moisture content of what I have and adjust the mass I add to the formula. Or doesn't it matter?

Any guidance would be appreciated.

Kevin
 

koraks

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opened it, used it, and not kept it in a dessicator I am guessing it is no longer completely anhydrous.

Is it all clumped up into one massive lump that resembles concrete and/or swimming in a puddle? Then you've got a problem.
Is it still a white powder with maybe a lump here and there? Don't worry, it's perfectly fine.
 

eli griggs

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Ditto; and don't go busting up lumps in the darkroom or kitchen.
 

JPD

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I have used the same anhydrous Sodium sulfite for about twenty years and it's fine, works as well as it did when "fresh". If there is a tiny bit of moisture in it it doesn't matter in developers that use the sulfite as the main alkali, because there is a lot of sulfite, and in developers that uses a small amount of sulfite it matters even less.
 

lamerko

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I have a now obsolete bank of sulfite. It's not in (big) lumps, but black little lumps have started to appear, which seem to get bigger over time. Could this be oxidation to sulfate, and if so, why are they black? Not that it really matters - sulfite is cheap, but I'm just curious what's going on inside...
 

lamerko

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Sulfate is white.

To know. That's exactly why I asked :smile:

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.
 

eli griggs

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To know. That's exactly why I asked :smile:

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 there is a college or advanced level student High School nearby, you might want to call their lead Chemistry Instructor and see if they are interested in having some of your chemical so students can learn or practice identifying contaminated in chemicals.

Black material sounds bad but if it's not changing your basic chemistry or become even inert material that scratches or otherwise damages your paper or film, you might still be able to use what you have.

Cheers
 

Petrochemist

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As your chemicals get damp you need to add a little more for the same effect. I've seen recipes using monohydrates & crystalline versions of reagents instead of the anhydrous grade, but sadly all too often the recipe actually fails to mention which it is!

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.
With a jar that started anhydrous it's very hard to know how much water it's picked up - I doubt you're set up to standardise it via titration, or do moisture content by Karl Fisher...
Heating to 100C will probably not drive off all the water - for some of our lab reagents it's recommended to heat them to 220C for at least 4 hours to get them dry - fortunately we have a vacuum oven which can dry at much lower temperatures. (Too expensive for my darkroom however)

Fortunately the weights in photographic formulations are normally not too critical, if one reagent is at slightly too low a concentration the mixture will usually work. It might work a little slower, create images a little less intense or go off a little quicker. Sodium Sulphite is often in a recipe to work as a preservative.

As for @lamerko 's black lumps - all sodium salts are white so the contamination must be down to something else - another metal such as Iron Sulphide (black) or coal... Disposal is probably best here!
 

koraks

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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.

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?
 

eli griggs

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Has anyone tried to dry out chemistry by using a small, hand held vacuum pump, and packaged of Sodium Silicates or a duel section Chemistry to a Loose Sodium Silicate to a steady pull vacuum pump assembly at the second transit port of the Silicates container or jar.

I suspect that three vacuum jars, ie, Bell Mason jars, with metal tops, ported through the lid tops with brass nipples, silver soldered for air tightness when a hose is attached, to the nipple of a two nippled lidded jar, to a second two nippled jar that ends with a hand vacuum pump, pulling vacuum.

Harbor Freight sells these nice hand vacuum pumps, for not a lot of dough, and they have a Mason Jar attachment, used for example, pulling out break fluids, with the Jars that can be of various capacity, for example, a two quart, a one quart, a pint, or a four ounce jar.

They all use the same dimension metal or plastic lids.

If you do this I'll suggest a good length of hose, from the chemistry jar, to the silicates jar, so the chemistry, if not light or heat sensitive, be set in a sunny warm window to get the moisture into gas from, to the shaded moisture collecting jar to the pump.

Cheers and let us know, please, if anyone here tries this out.

Eli

PS: it occured to me that an indicator that will actually show you if the silicates jar is capturing moisture could be simply made, by taking small pieces of pointed or balled metal, and piercing the lid, inserting each down into the jar side of the metal lid and soldering them in place for a non-venting install.

Imagine using kids metal "Jacks" as the probes, ball ends as the 'drip probes' inside the jar, where condensation can form on them and drip dow into the silicates.

There's no need to cut the jacks, just drill the holes where there is easy
Access to the jar lid plate for about three - four Jack ball points, solder and let the drips be your guide to when the setup is working, you might even try putting a small copper dish, on top of the Jacks standing proud of the outside lid top, with some ice in it, to give the jacks the thermal advantage of greater condensations.

My suggestion for brass ports hose connections, is to take fired .22 Rimfire brass, primer discharged, the bottom inside drilled out, so the rim can form a tighter fitting flange for soldering the case through the top of the lid, for thin hose attachments.

Mason jars and new metal lids are available at Walmart and various hoses at Home Depot or Lowes home centers.


The name of the vacuum pump from HF is, "Mity Vac"


Photo road trip related equipment is the gas cap tester pump and caps kit.

It will allow you to check your car's gas cap seal to see if it will properly seal for better gas mileage which can be turned into more/longer photo road trips, film, etc.
 
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koraks

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Has anyone tried to dry out chemistry by using a small, hand held vacuum pump

No. I just store my sulfite in this:
1715149274561.png

That way it doesn't need any Rube Goldberg contraption. Just a simple tub.

I did once, for the heck of it, dry sodium carbonate decahydrate to obtain the anhydrous form. Just spread it out in an oven tray and bake it for half an hour until the water is gone. I did this only once, because it has no practical utility. Again, Mr Goldberg can stay in bed.

Why would all this have to be made so damn complicated? It's totally unnecessary!
 

Petrochemist

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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?
Quite sure, it's going back to my school days as I mainly work with organics but hardly difficult stuff.

I don't normally use CAS numbers, chemical structures are simpler to work out without using an index.
I guess CAS numbers can help with complex organic molecules (such as Metol which is 'p-methylaminophenol sulfate' named systematically) or mixtures such as gasoline...

There is not a huge little difference in weight between the two.
Sodium Sulphite is Na2SO3 with a RMM of 126 (anhydrous) The monohydrate is Na2SO3.H2O
Sodium Carbonate is Na2CO3 with a RMM of 106 (anhydrous) The monohydrate is Na2SO3.H2O its fully hydrated crystalline form is the decahydrate Na2CO3.10H2O

In each case adding a molecule of water of crystallisation will add 18 to the molecular weight (in both cases the decahydrate will have more mass of water than the sodium salt)

For Sodium Sulphite that's 144/126 or 1.14x to use the monohydrate instead of anhydrous
with the carbonate its 114/106 or 1.07x
 
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koraks

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I don't normally use CAS numbers

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.

In each case adding a molecule of water of crystallisation will add 18 to the molecular weight

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.
 

Petrochemist

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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 gather Crystalline is a layman's term for the fully hydrated form. It's not something I've come across at work, FWIW we usually get anhydrous reagents here in the UK.
I have seen crystalline used in photographic books for quite a few reagents.
Sadly all too often the hydration is ignored in formulae & you have to guess which form the weight applies to. My old (2nd ed) copy of the Darkroom cookbook is particularly bad for this, as it doesn't even seem to be consistent.
 

koraks

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I have seen crystalline used in photographic books for quite a few reagents.

Yes, mostly sodium carbonate.

My point is that's easy to create confusion - it's difficult to remove it once it's there. People come back to information like this, get confused and worry about what kind of sulfite they have, won't be able to figure out etc. In this case, there's just no practical concern, no need to calculate anything or be confused about anything. So I advocate to keep it simple.

If this were about carbonate, I'd be all for making the nuances, talking about conversion factors etc!
 

eli griggs

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Why would all this have to be made so damn complicated? It's totally unnecessary!

Because it's a question that challenges (some) people that don't mind being involved in a solution others may be afraid to try, are content with "good enough for Government work" or simply disinterested in possibilities.

The nice thing here, is no one is holding a pie to anyone's head!

It's also fun to see if your particular "Rube Goldberg" contraption will actually work and how well it does function, if working at all.
 
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