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  1. #1
    BradS's Avatar
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    making sodium carbonate (anhydrous) at home?

    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).

  2. #2

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    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.

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    Quote Originally Posted by 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.

    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

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    Quote Originally Posted by 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).
    .

    Why? Just use the conversion factor.


    Wayne

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    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.

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    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.

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    Quote Originally Posted by 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

  8. #8

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    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.

  9. #9
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    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

  10. #10
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    Quote Originally Posted by 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.
    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.

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