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] |