making sodium carbonate (anhydrous) at home?

[BradS]

I've just cooked a freshly opened one pound box of baking soda in a convection oven at 350 degrees F for a little over an hour (I poured it outinto a baking dish and stired gently every fifteen minutes or so).

Now, if I understand correctly, I have a little less than a pound of Sodium Carbonate (anhydrous). Right?

How can I test this?

Damn! I should have worn a dust mask...(cough, cough....aarrrrgh).

 

[jim appleyard]

I don't think so (chemists please correct me if wrong). I think sod. bicarb and sod. carb are two different critters. I've read that if you do what you did to Arm & Hammer Washing Soda, then you'd have anhydrous sod. carb.

 

[Maine-iac]

I don't think so (chemists please correct me if wrong). I think sod. bicarb and sod. carb are two different critters. I've read that if you do what you did to Arm & Hammer Washing Soda, then you'd have anhydrous sod. carb.

This is incorrect. Arm&Hammer Washing soda is sodium carbonate, although not the anhydrous variety. However, in any developer formula I've ever tried, and I've experimented with many, it doesn't make any difference whether you use the anhydrous variety or not. Once exposed to air, over time, it will cease being the anhydrous form anyway.

And there's no need to convert bicarb into carb anyway, since both are readily available in the supermarket. phPlus at a swimming pool store is also perfectly good photographic grade carbonate.

Larry

 

[Wayne]

I've just cooked a freshly opened one pound box of baking soda in a convection oven at 350 degrees F for a little over an hour (I poured it outinto a baking dish and stired gently every fifteen minutes or so).
.

Why? Just use the conversion factor.


Wayne

 

[Gerald Koch]

When heated sodium bicarbonate is converted to sodium carbonate and carbon dioxide gas. Why would you want to do this? To obtain a very pure form of sodium carbonate since the baking soda that you start with is USP grade. Arm & Hammer washing soda and the various pool products used to adjust pH are the technical grade. Another reason, sometimes one cannot obtain sodium carbonate but baking soda is readily available everywhere.

The reaction is 2NaHCO3 --> Na2CO3 + H2O + CO2 and 2 moles of sodium bicarbonate (2 x 84 g) will produce 1 mole of sodium carbonate (106 g) or 1 lb of baking soda will produce 10 oz of sodium carbonate. The fine crystalline powder of the baking soda will become a very light fluffy powder which is the anhydrous sodium carbonate.

 

[psvensson]

Another way to make a solution of sodium carbonate would be to add sodium hydroxide to a solution of sodium bicarbonate. No need for heating, but you'd end up with a solution, not dry powder. The chemists here could probably tell you the ratios, if you're interested.

 

[Wayne]

Why? Just use the conversion factor.


Wayne

Oops. I thought you baked A&H Washing Soda, not baking soda. There is no conversion factor for that. Nevermind


Wayne

 

[lowellh]

Since we buy chemicals in bulk, I know how difficult it is to find photo grade sodium carbonate, we have converted our formulas to Potassium Carbonate, which is readily available.

 

[Photo Engineer]

One thing that is not commonly known is that potassium salts will poison a fix and slow down fixing very rapidly.

This is why major manufacturers do NOT use potassium carbonate in developers. If enough is carried over, the seasoning effect will stop the fixation reaction. See Mees or Mees and James for this information.

PE

 

[BradS]

When heated sodium bicarbonate is converted to sodium carbonate and carbon dioxide gas. Why would you want to do this? To obtain a very pure form of sodium carbonate since the baking soda that you start with is USP grade. Arm & Hammer washing soda and the various pool products used to adjust pH are the technical grade. Another reason, sometimes one cannot obtain sodium carbonate but baking soda is readily available everywhere.

The reaction is 2NaHCO3 --> Na2CO3 + H2O + CO2 and 2 moles of sodium bicarbonate (2 x 84 g) will produce 1 mole of sodium carbonate (106 g) or 1 lb of baking soda will produce 10 oz of sodium carbonate. The fine crystalline powder of the baking soda will become a very light fluffy powder which is the anhydrous sodium carbonate.

Ah, Excellent! This is why it works. I weighed the product of this process and found it to weigh approximately 295 grams. I started with a one pound box - nominally 454 grams. 295/ 454 is pretty darnd close to the 10 / 16 that you speak of in your post. So, it looks like it works!

Thanks all!

Brad.

 

[dancqu]

Once exposed to air, over time, it will cease being
the anhydrous form anyway. Larry

You are saying the anhydrous will absorb H2O from
the air. I think that true. I believe the mono-hydrate
is the most stable of the carbonates. It is most often
the form mentioned.

Years ago I placed some bicarbonate in boiling water
and it effervesced greatly. What was left? A mix of
two or just the carbonate? Dan

 

[gainer]

A mixture of sodium carbonate, water and carbonic acid. Maybe about as much carbonic acid as is left in pepsi after you boil it.

 

[raucousimages]

Sounds like a lot of work. I buy it for $4.00/LB from a local chemical supplyer.

 

[BradS]

Sounds like a lot of work. I buy it for $4.00/LB from a local chemical supplyer.

Some say that developing film is a lotta work too. I did it because I had read about the process and wanted to try it. It really wasn't much work.....turn on the oven , go to the pantry and get a box of baking soda, open the box and pour it out into a baking tray, put it in the oven and set a timer. Surf the net while watching the timer. Get up and give the powder a stir every once in a while.

I can buy sodium carbonate from the local supplier too but, I'd have to drive 40 miles round trip and then they'd want to give my name, address and driver's license number to the US Department of Homeland Security. I'd have to live life watching over my shoulder all the time...what a pain.

Baking soda cost $1.20 per pound at the local grocery store...and, I can walk there.

I'd rather cook baking soda.

 

[gainer]

Order it from www.chemistrystore.com. They ship it to your house. Get 25 pounds, they don't care. Use it to make your own detergents. A mixture with clorox is a a very good cleaner for bathtubs and the like.

 

[Maine-iac]

Sounds like a lot of work. I buy it for $4.00/LB from a local chemical supplyer.

I pay about $2.00 for a two-pound box of Washing Soda at our grocery store. Makes a heck of lot of developer. Arm & Hammer has also removed all or most of the objectionable perfume smell they gave it several years ago. The newer stuff doesn't have much of an odor at all.

Larry

 

[lowellh]

The same can be said for a very small amount of fixer getting into the developer. It will poison the developer. We have not found your fears or carry over issue to be a concern. Perhapse it is because there is not enough potassium salt in the developer to become an issue.

 

[Photo Engineer]

The same can be said for a very small amount of fixer getting into the developer. It will poison the developer. We have not found your fears or carry over issue to be a concern. Perhapse it is because there is not enough potassium salt in the developer to become an issue.

The difference being that you normally do not process in reverse, so that fixer getting into the developer is less common than developer getting into the stop and fix. In fact, getting developer into the stop and fix is an assured event. The reverse is an accident.

The data are to be found in Mees and James along with the tests they ran. Potassium ion is not good in fixers. The rate of slowdown is easily measured, but, not knowing your developer formula, I could not predict the rate of change.

PE

 

[Gerald Koch]

The amount of carry over of developer into the fixing bath would have to be large. However, most people use some sort of stopbath even if it is only water rinse. So the amount of potassium ion reaching the fixer would be very small. I don't see the transfer of potassium ion to the fixer to be a serious problem.

 

[Photo Engineer]

The amount of carry over of developer into the fixing bath would have to be large. However, most people use some sort of stopbath even if it is only water rinse. So the amount of potassium ion reaching the fixer would be very small. I don't see the transfer of potassium ion to the fixer to be a serious problem.

Gerald, you may or may not be right. IDK.

I know that when I was designing developers at EK, they taught us to avoid potassium carbonate in developers 'just in case'. And, never use them in fixers.

Then I had to read some reports on the subject to show what happened with seasoned processes that used potassium salts in the developer, and reports on testing potassium salts in the fixer. So, I pretty much avoid them. It is possible to use them at rather low concentrations or to use certain potassium salts in developers.

PE

 

[Gerald Koch]

Potassium ion only becomes a problem when you are dealing with rather high concentrations. The amount of carry over is negliable when using a stopbath or rinse. IIRC, the problem with potassium ion slowing the rate of fixation was first noticed with certain Agfa fixer formulas which contained potassium thiosulfate instead of the sodium or ammonium salt.

 

[Photo Engineer]

Potassium ion only becomes a problem when you are dealing with rather high concentrations. The amount of carry over is negliable when using a stopbath or rinse. IIRC, the problem with potassium ion slowing the rate of fixation was first noticed with certain Agfa fixer formulas which contained potassium thiosulfate instead of the sodium or ammonium salt.

Gerald;

I'm not sure about the Agfa fixer you mention above, but Mees reported on the effects of potassium salts on fixation as early as the 1954 edition of his book, and internal Kodak reports warned of it in the design of developers (no potassium carbonate) and the design of fixers (no potassium salts).

AFAIK, that is true today in all Kodak formulations.

Mees specifically stated that use of potassium hypo reduced fix rates by about 4x. Therefore, some level of reduction in fix rate could be expected as a fixer 'seasons' by carried over developer if the amount of potassium carbonate were to be high enough to survive the stop or rinse in a reasonable amount.

My opinion, with no concrete data is this: "Why take a chance?" Besides, sodium salts are less expensive and easier to get and have no significant adverse effect on fixation. This does not mean that they cannot be used, or that low levels are to be avoided. I have used KBr in developers as an antifoggant with no concernt about any effect on fixation due to the low level used. Potassium Sulfite might be useful in developers as well.

PE

 

[dancqu]

Mees specifically stated that use of
potassium hypo reduced fix rates by ...
PE

Reduced fix rates! Well there goes my theory. I've never
seen it spelled out; how does potassium negatively affect
fixation. So I theorised.

In solution we have the ammonium and/or sodium ions and
the silver complexed with thiosulfate; the argentothiosulfate
ion. Now the ammonium and sodium salts of that complex ion
are very soluble while the potassium salt is only sparingly
soluble. I suppose that would affect the "rate" but I'd
think Capacity would be the issue. Dan

 

[Photo Engineer]

Reduced fix rates! Well there goes my theory. I've never
seen it spelled out; how does potassium negatively affect
fixation. So I theorised.

In solution we have the ammonium and/or sodium ions and
the silver complexed with thiosulfate; the argentothiosulfate
ion. Now the ammonium and sodium salts of that complex ion
are very soluble while the potassium salt is only sparingly
soluble. I suppose that would affect the "rate" but I'd
think Capacity would be the issue. Dan

What theory was that Dan?

But yes, both rate and capacity may be influenced, or it may just seem that capacity is influenced by potassium as the rate becomes (or is) so slow.

IDK the reason, but it could be that the counter ion is closely associated with the many silver thiosulfate complexes.

Mees cites a phase rule diagram and shows that 4 different sodium argentothiosulfates vary from very slightly soluable through sparingly soluable, to readily soluable. The same is probably true of potassium salts, but with ammonium salts, the ammonium ion can become part of the acutal complex and influence rate, being very much smaller than a thiosulfate ion. This can influence diffusion rates.

It is very complex (pun intended), and I studied it for several years working on blixes and fixes for color materials.

PE

 

[Tom1956]

Perfectly ignorant question

Please excuse my laziness in asking a chemistry question. It's been many years since college chemistry and am not finding a lot of help in answering my question in the chemical forums. I just finished baking sodium bicarbonate to get my carbonate ready for when my metol gets here so I can dive in to my Buetlers developer testing.
I started out with 230 grams of bicarb from the grocery store, and now have 173g of powder after baking for an hour at 350 or so. Was my conversion complete, or do I need to get out a cookpot on the stove and cook it a little longer? Thanks.