vano
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Technical sodium molybdate
Hello. Does anyone know what impurities are in technical sodium molybdate dihydrate and what is percentage of sodium molybdate.
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Bedlasky
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If you have burette, you can estimate molybdate content by iodometry.
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vano
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Unfortunately I don't have
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What equipment do you have?
Do you have a good balance?
It might be possible to precipitate something like calcium molybdate and weigh that.
In any event, if you recrystalise the stuff, you will almost certainly get a higher purity product.
My best guess would be that the dominant impurities would be chromium and tungsten.
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Bedlasky
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Molybdenum can be also estimated gravimetrically as 8-hydroxyquinolinate (if you have decent scales). Add 8-hydroxyquinoline slowly with constant
stirring, both solutions (molybdate and 8-hydroxyquinoline) must be dilute (to avoid error by occlusion).
http://chemistry.uohyd.ac.in/~mvr/ch306/oxine.pdf
More about gravimetry here:
https://chem.libretexts.org/Bookshelves/Analytical_Chemistry...
Edit: Impurities like Cr, W can precipitate alongside Mo. I read about method to precipitate Mo as MoS3 and then ignite it at certain temperature to
obtain MoO3. Mo can be seperated from W if you follow procedure. But this determination is really laborious and you need good temperature control
during igniting MoS3, because if temperature is too high, you lost some MoO3 by sublimation.
https://sci-hub.se/https://pubs.acs.org/doi/pdf/10.1021/ja01...
Anyway I don't think that your sodium molybdate have much impurities. It is used in agriculture, so I don't expect high concentrations of other
metals.
[Edited on 6-8-2021 by Bedlasky]
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vano
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Quote: Originally posted by Bedlasky  | Molybdenum can be also estimated gravimetrically as 8-hydroxyquinolinate (if you have decent scales). Add 8-hydroxyquinoline slowly with constant
stirring, both solutions (molybdate and 8-hydroxyquinoline) must be dilute (to avoid error by occlusion).
http://chemistry.uohyd.ac.in/~mvr/ch306/oxine.pdf
More about gravimetry here:
https://chem.libretexts.org/Bookshelves/Analytical_Chemistry...
Edit: Impurities like Cr, W can precipitate alongside Mo. I read about method to precipitate Mo as MoS3 and then ignite it at certain temperature to
obtain MoO3. Mo can be seperated from W if you follow procedure. But this determination is really laborious and you need good temperature control
during igniting MoS3, because if temperature is too high, you lost some MoO3 by sublimation.
https://sci-hub.se/https://pubs.acs.org/doi/pdf/10.1021/ja01...
Anyway I don't think that your sodium molybdate have much impurities. It is used in agriculture, so I don't expect high concentrations of other
metals.
[Edited on 6-8-2021 by Bedlasky] |
Thank you Bedlasky!
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maldi-tof
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Typical impurities for sodium molybdate are arsenic and potassium.
You can "check" at least if it is the 2-hydrate carrying out a loss on drying test at 140°C (it should be between 14.0-16.0% per Eu. Ph.).
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Bedlasky
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Arsenic? Are you sure? I doubt that someone add something that contain arsenic in to the soil.
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maldi-tof
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One source that we have for sodium molybdate 2-hydrate has 0.01% of arsenic (100 ppm).
If it is a "natural" product, it is not strange that some sources of molybdenum that have not been treated or purified contain arsenic as impurity.
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