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  1. #1
    Bruce Osgood's Avatar
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    Sodium Carbonate replacement

    I'm re-examining many of my long time assumptions:

    When using Arm & Hammer washing soda in place of Sodium carbonate is it used as a mono-hydrate or anhydrous?

    TIA,

  2. #2

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    anyhydrous

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    i think.

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    Bruce Osgood's Avatar
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    Quote Originally Posted by Wayne View Post
    i think.

    OOP'S, you're in the same boat as I am....

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    Everything I've been able to find online indicates that the monohydrate is the most stable form---the others tend to change into it over time in normal storage conditions. You can get it in the anhydrous form (e.g., from the Formulary), but in a cardboard washing-soda box it would pick up water molecules from the air and turn into monohydrate even if it didn't start that way.

    Disclaimer: I'm repeating what I've read, so I'm only as sure as my trust in my sources (which, however, include some of the Actual Chemists here on APUG).

    -NT
    Nathan Tenny
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  6. #6

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    This states that Arm & Hammer Washing Soda is 85% sodium carbonate, 15% water, so itís probably not anhydrous.

    http://hpd.nlm.nih.gov/cgi-bin/house...nds&id=3005022

    The monohydrate form has a mass of about 124g/mol, while the anhydrous form is about 106g/mol.

    (106g/mol)/(124g/mol) = 0.85, which is about the stated percentage of sodium carbonate in Arm & Hammer Washing Soda.

    Based on this, my estimate is that itís the monohydrate form.

    Perhaps one of our experienced chemists will contribute an authoritative answer.

  7. #7

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    i suppose you could force out some of the water
    by heating it up in your oven on a cookie sheet
    the same way you would "convert" baking soda into
    sodium carbonate.

  8. #8

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    It is the monohydrate form and is essentially technical grade and contains a small amount of sodium chloride and a smaller amount of iron. It is good enough for paper developers but not for ascorbate developers where the iron may be a problem.

    A purer form can be obtained by heating Arm & Hammer Bicarbonate of Soda which is USP grade. I would recommend doing this for developers such as Xtol substitutes and for the Beutler formula.
    Last edited by Gerald C Koch; 11-19-2011 at 02:32 PM. Click to view previous post history.
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