Monohydrous vs. Anhydrous query (sodium sulphite and others)

[Ashfaque]

I received a few raw chemicals from a local chemical seller in Dhaka. Well, they were packed in cheap ar#e polythene bags. FYI, they came from large bulks and it is quite humid in Dhaka. But I didn't notice any watery stuffs in any. But my guess is they've began to be monohyrdate. (I can try do a test by putting a sample 100 grams of each chemical in the oven and measure the weights pre and post cook. But our kitchen is busy). Since my chemistry knowledge is pretty basic, I need your help.

(1) If a formula tells me to add 100 grams sodium sulphite (for e.g., (there was a url link here which no longer exists), or 'Perceptol type'), should I stick to 100 grams or more?
(2) I understand that sodium cardbonate (anhy) or potassium carbonate (anhy), once opened, quickly becomes monohydrous and consequently will need to (there was a url link here which no longer exists). What about sodium meta bisulphite and potassium meta bisuphite?

Also, can I safely store metol in a clear glass bottle (with plastic cap), in the back of a cabinate (relatively dark, quite dry and always away from direct sunlight)? I asked for 50 grams of metol, but he sent me 500 grams. I don't know how long it'll take me to finish that much!

Bests,
Ashfaque

 

[Ian Grant]

In the UK the monohydrate form is unusual that's how it's made/sold in the US.

Get some decent containers and they shouldn't deteriorate, if they absorb too much water they'll solidify to a solid mass anyway. The Metabisulphite must be kept an a tightly sealed container, that deteriorates the fastest of those three you mention.

Ian

 

[Ashfaque]

Thanks Ian. What about adjustng the amount from anhydrous to monohydrous?

 

[Gerald C Koch]

Usually the most stable hydrate is what is sold. (The exception appears to be washing soda sold in the UK which is the decahydrate.) This would be sodium carbonate, monohydrate and sodium sulfite, anhydrous. If no version is specified in a formula then too most often it is the stable form. This is fairly standard practice.

When converting from one form to another calculate the molecular weights of each and then the ratio. Then use this ratio to calculate a conversion factor. Molecular weightsbe found on the net.

 

[Ian Grant]

With Sodium Carbonate the conversion is 1.2g Monohydrate for 1g Anhydrous.

Many errors in Formulae come from incorrect conversions of Anhydrous, Monohydrated, Anhydrous etc the Photo Lab Index is full of them. Surprisingly Agfa Ansco made a couple of conversions the wrong way with German Agfa formulae.

In the US Sodium Carbonate was always found as the Monohydrate but in Europe it's always the Anhydrous form now but at one time it was the Crystalline form.

Ian

 

[pdeeh]

I'd be surprised if someone using a hand tank and developing a couple of rolls a month in their kitchen would ever be able to notice the difference between D23/D76 variations made with mono- or anhydrous sulfite, or carbonates for other types of developer, unless they also had an extremely strictly strict regime of calibration via densitometry throughout the rest of their processes ...

 

[JW PHOTO]

So, if you happen to find sodium carbonate or sodium sulfite that somehow managed to hide itself in the corner of you chemical storage area for the last two or three years should you automatically consider it monohydrate?

 

[JW PHOTO]

Not in the case of sodium sulfite. I suppose it could be anything between anhydrous and crystalline (decahydrate). How caked or clumped it looks might give some hints, but nothing conclusive without testing. In the end the hydration state of really old sodium sulfite is less of a concern than whether or not it is still sulfite. Over time with exposure to air sodium sulfite oxidizes to sodium sulfate.

Thanks Michael, I have never had Sodium Sulfite cake on me, but I've never kept it longer then two years. Those two years of storage were is a sealed Boston Brown jars. I have a 20lb. round cardboard drum of Kodak Kodalk from "who knows when" that I still use and seem to have no problems with it. I don't know how much moisture it has absorbed through that old cardboard drum, but I haven't even tried to allow for it in any of my measurements and seem to be okay.

 

[Ashfaque]

Thanks everyone. The sodium sulphite and other chemicals I received are quite dry. No clumps. Time to buy some wide mouth bottles.

Bests,
Ashfaque

 

[Wayne]

Over time with exposure to air sodium sulfite oxidizes to sodium sulfate.

Is there a practical way to test it to know?

 

[Gerald C Koch]

Is there a practical way to test it to know?

NO you would need an analytical balance and other equipment. In the lab you would first weigh a sample and then place the sample in a dessicator. After several days you would reweigh the sample and note any difference in weight.

 

[Wayne]

NO you would need an analytical balance and other equipment. In the lab you would first weigh a sample and then place the sample in a dessicator. After several days you would reweigh the sample and note any difference in weight.

Oh. Then what would MacGyver do?

 

[removed account4]

Oh. Then what would MacGyver do?

if it was sodium carbonate macgyver would probably put it in his toast-R-oven and toast it for a while to dry it out.
then he'd do whatever it was he was gonna do with it ... no idea what he'd do with that other stuff ...
probably put in a desiccator for a few days and weigh the sample
I have feeling Gerald and Ron are both mild mannered chemists here
but totally macgyvers on the side

 

[JW PHOTO]

if it was sodium carbonate macgyver would probably put it in his toast-R-oven and toast it for a while to dry it out.
then he'd do whatever it was he was gonna do with it ... no idea what he'd do with that other stuff ...
probably put in a desiccator for a few days and weigh the sample
I have feeling Gerald and Ron are both mild mannered chemists here
but totally macgyvers on the side

John,
I've done the oven thing with Sodium Carbonate, but don't waste my time anymore. I just figure my old store-bought box is now in the monohydrous state and adjust by weight instead of wasting energy converting it back to anhydrous state. Seems to work okay for me and saves time too. John W

 

[Wayne]

John,
I've done the oven thing with Sodium Carbonate, but don't waste my time anymore. I just figure my old store-bought box is now in the monohydrous state and adjust by weight instead of wasting energy converting it back to anhydrous state. Seems to work okay for me and saves time too. John W

If its in the yellow box with the arm and hammer on it its monohydrate when you buy it.

 

[Wayne]

if it was sodium carbonate macgyver would probably put it in his toast-R-oven and toast it for a while to dry it out.
then he'd do whatever it was he was gonna do with it ... no idea what he'd do with that other stuff ...
probably put in a desiccator for a few days and weigh the sample
I have feeling Gerald and Ron are both mild mannered chemists here
but totally macgyvers on the side

I don't think MacGyver would care about the sodium carbonate because he'd know its still sodium carbonate. However he'd want to know if his sulfite had become sulfate. And I'd like to know if mine has too.

 

[removed account4]

his mono carbonate might have become bi carbonate .. no?

 

[Gerald C Koch]

I don't think MacGyver would care about the sodium carbonate because he'd know its still sodium carbonate. However he'd want to know if his sulfite had become sulfate. And I'd like to know if mine has too.

Lacking an analytical laboratory there is no way of determining the extent of any oxidation. Best to keep sodium sulfite in air-tight containers. I always transfer it to canning jars. They are cheap, come in several sizes and readily available especially during canning season.

 

[pdeeh]

Shouldn;t that be canning cans or bottling jars?

 

[JW PHOTO]

We always called them plain old canning jars. Screw on rings with rubber seal lids. When I was real little we used some glass Mason jars with attached glass tops. The tops took a replaceable red rubber seal.