soda ash

Discussion in 'B&W: Film, Paper, Chemistry' started by dpodeath, Feb 14, 2009.

  1. dpodeath

    dpodeath Member

    Feb 24, 2004
    i recently bought some Soda ash to use in formulas as sodium carbonate but what i cant figure out is what kind it is... monohydrate? anhydrous?

    the MSDS says...

    Ingredient CAS Number Weight %
    Sodium Carbonate 497-19-8 99.8%

    Physical and Chemical Properties
    Physical State Solid
    Specific Gravity 2.533 (vs. water)
    Bulk Density g/l Dense grades: 0.9-1.1
    Natural light grade: 0.7- 0.9
    Synthetic light grade: 0.5 – 0.7
    Color/Appearance White, granular solid
    Odor None
    Boiling/Cond. Point decomposes (boiling point)
    Melting/Freezing Point 854oC (1569oF) (melting point)
    Solubility Complete
    Evaporation Rate Not applicable
    VOC % not Applicable
    Percent Volatile 0%
    Molecular Formula Na2CO3
    Viscosity Not applicable
    Vapor Density Not applicable
    Vapor Pressure Not applicable
    pH (1% solution) 11.3

    I figure if the CAS number matches with the one on Wikipedia it has to be Anhydrous.

    help please!

  2. Ian Grant

    Ian Grant Subscriber
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    Aug 2, 2004
    West Midland
    Multi Format
    Most Soda ash is the crystalline form of Sodium Carbonate, but it can vary. For this reason it's best to buy specific grades. The anhydrous form is generally called Light Soda, (well in the UK anyway), I used to buy it 100-400 Kilos at a time, in 25kg bags.

    I think BradS posted a way of drying in a normal oven to form the anhydrous version.

  3. Murray Kelly

    Murray Kelly Subscriber
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    Jan 31, 2007
    Brisbane, QLD
    Multi Format
    Sheesh - that's almost half a ton! =8-0

  4. gainer

    gainer Subscriber

    Sep 20, 2002
    The formula and the molecular weight given are those for anhydrous sodium carbonate. If it had water of crystallization, the number of water molecules should be included in the molecular formula. Actual purity is claimed to be 99.8%. To find out if it has excess water, weigh a half cup of it, heat it above the boiling point of water, but not too much above, for a considerable time, say 30 minutes, and weigh it again. If it was originally washing soda, the weight loss will be considerable. If you use the oven, 300 F will be sufficient.

    If washing soda is sold as soda ash, you are being cheated. It has 10 molecules of water for each molecule of Na2CO3. There is another form with 7 molecules of water, and there is the monohydrate which is IIRC the most stable, the one that the others arrive at when left long enough in open air.
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