Sodium sulfite anhydrous vs non anhydrous

[MingMingPhoto]

hello!
in the film developing cook book some chemicals are anhydrous and some are non depending on the formula.

can I use these tow chemicals interchangeably?

what are the differences between the two?

 

[Ian Grant]

100f Sodium Sulphite anhydrous is equivalent to 200g crystalline, so a simple calculation.

Ian

 

[JPD]

Some chemicals are hygroscopic, they absorb moisture from the air and form crystals, so they are often sold as crystalline. Sodium carbonate is one, and the decahydrate is the most stable form, but it's lumpy so I prefer the anhydrous (dry) powder or monohydrate and keep the powder dry with the lid on. https://www.photrio.com/forum/threads/sodium-carbonate-monohydrate-vs-anhydrous.177015/

Sodium sulfite keeps well as anhydrous so it's easy to find, and most formulas call for anhydrous, but it you have the crystalline version just double it like Ian said.

 

[MingMingPhoto]

Some chemicals are hygroscopic, they absorb moisture from the air and form crystals, so they are often sold as crystalline. Sodium carbonate is one, and the decahydrate is the most stable form, but it's lumpy so I prefer the anhydrous (dry) powder or monohydrate and keep the powder dry with the lid on. https://www.photrio.com/forum/threads/sodium-carbonate-monohydrate-vs-anhydrous.177015/

Sodium sulfite keeps well as anhydrous so it's easy to find, and most formulas call for anhydrous, but it you have the crystalline version just double it like Ian said.

ok so I don't know anything about chemcials. are you using any words in your explincation interchangibly? if so can you clearify?

100f Sodium Sulphite anhydrous is equivalent to 200g crystalline, so a simple calculation.

Ian

are you able to list all the various forms of sodium sulfite?

 

[JPD]

Ok, I think saying that the decahydrate is the most stable form of Sodium carbonate was a mistake, that should be the monohydrate.

ok so I don't know anything about chemcials. are you using any words in your explincation interchangibly? if so can you clearify?

The different forms of hydrates means how much water the powder/crystals have. For example the Sodium carbonate I mentioned: https://en.wikipedia.org/wiki/Sodium_carbonate

Sodium carbonate is obtained as three hydrates and as the anhydrous salt:​

• sodium carbonate decahydrate (natron), Na2CO3·10H2O, which readily effloresces to form the monohydrate.
• sodium carbonate heptahydrate (not known in mineral form), Na2CO3·7H2O.
• sodium carbonate monohydrate (thermonatrite), Na2CO3·H2O. Also known as crystal carbonate.
• anhydrous sodium carbonate (natrite), also known as calcined soda, is formed by heating the hydrates. It is also formed when sodium hydrogencarbonate is heated (calcined) e.g. in the final step of the Solvay process.

I'm not a chemist but learn when I need to. I have to look at notes or search on forums when a formula calls for anhydrous and I have crystalline or vice versa.

 

[koraks]

are you able to list all the various forms of sodium sulfite?

There are only two. Anhydrous and hydrate, which is technically the heptahydrate (contains 7 water molecules per sulfite molecule).

All the times I bought sulfite, it was anhydrous. I'm not sure how common the heptahydrate is in the marketplace. If you have/receive a relatively free-flowing, fine powder, it's most likely anhydrous.

 

[MingMingPhoto]

There are only two. Anhydrous and hydrate, which is technically the heptahydrate (contains 7 water molecules per sulfite molecule).

All the times I bought sulfite, it was anhydrous. I'm not sure how common the heptahydrate is in the marketplace. If you have/receive a relatively free-flowing, fine powder, it's most likely anhydrous.

if you know why, would you mind explaining why you say there are only two but other people on this thread are saying there are more than two?

Ok, I think saying that the decahydrate is the most stable form of Sodium carbonate was a mistake, that should be the monohydrate.



The different forms of hydrates means how much water the powder/crystals have. For example the Sodium carbonate I mentioned: https://en.wikipedia.org/wiki/Sodium_carbonate

Sodium carbonate is obtained as three hydrates and as the anhydrous salt:​

• sodium carbonate decahydrate (natron), Na2CO3·10H2O, which readily effloresces to form the monohydrate.
• sodium carbonate heptahydrate (not known in mineral form), Na2CO3·7H2O.
• sodium carbonate monohydrate (thermonatrite), Na2CO3·H2O. Also known as crystal carbonate.
• anhydrous sodium carbonate (natrite), also known as calcined soda, is formed by heating the hydrates. It is also formed when sodium hydrogencarbonate is heated (calcined) e.g. in the final step of the Solvay process.

I'm not a chemist but learn when I need to. I have to look at notes or search on forums when a formula calls for anhydrous and I have crystalline or vice versa.

so when buying sodium sulfite it will come in one of these four versions?

 

[koraks]

if you know why, would you mind explaining why you say there are only two but other people on this thread are saying there are more than two?

@JPD is talking about sodium carbonate. Your question and my comments about only two species referred to sodium sulfite.

 

[MingMingPhoto]

@JPD is talking about sodium carbonate. Your question and my comments about only two species referred to sodium sulfite.

ah silly me, I didn't realize he brought that into the equation. thank you for clarifying.

There are only two. Anhydrous and hydrate, which is technically the heptahydrate (contains 7 water molecules per sulfite molecule).

All the times I bought sulfite, it was anhydrous. I'm not sure how common the heptahydrate is in the marketplace. If you have/receive a relatively free-flowing, fine powder, it's most likely anhydrous.

if it's crystaline will it be the hydrate version? If a formula calls for one or the other is there a problem if I actually the other version?

 

[koraks]

if it's crystaline will it be the hydrate version?

The hydrate is also crystalline, so that makes it a little confusing. What you could try is take e.g. 10g, then bake it for half an hour in an oven at e.g. 150C and weigh it again. If it's anhydrous, it'll still be 10g. If it was the heptahydrate, it should have lost its water and the weight will be considerably less; roughly half of what you started with (5g).

However...I don't think you can commonly buy the heptahydrate. The anhydrous form is the one that's usually sold, because it's more stable; the heptahydrate oxidizes all by itself (due to the presence of water), so doesn't keep well.

If a formula calls for one or the other is there a problem if I actually the other version?

Not if you correct for the different weights. See the experiment above als @Ian Grant's initial reply. But really, if you buy some, odds are you'll have anhydrous anyway, so you should be good.

 

[MingMingPhoto]

The hydrate is also crystalline, so that makes it a little confusing. What you could try is take e.g. 10g, then bake it for half an hour in an oven at e.g. 150C and weigh it again. If it's anhydrous, it'll still be 10g. If it was the heptahydrate, it should have lost its water and the weight will be considerably less; roughly half of what you started with (5g).

However...I don't think you can commonly buy the heptahydrate. The anhydrous form is the one that's usually sold, because it's more stable; the heptahydrate oxidizes all by itself (due to the presence of water), so doesn't keep well.



Not if you correct for the different weights. See the experiment above als @Ian Grant's initial reply. But really, if you buy some, odds are you'll have anhydrous anyway, so you should be good.

so baking the more watered version effectively makes it into the anhydrous version correct?

 

[MattKing]

so baking the more watered version effectively makes it into the anhydrous version correct?

Correct - unless you leave it out in the air, in which case it will gradually become the more watered version.

 

[koraks]

so baking the more watered version effectively makes it into the anhydrous version correct?

Exactly, and also what @MattKing says - it'll absorb moisture from the atmosphere again, but if you keep it in a sealed jar, this will be negligible.

But really - don't worry about this. Just buy some sulfite, use as indicated in whatever formula you mix. Don't overthink it.