Sciencemadness Discussion Board

Technical sodium molybdate

vano - 6-8-2021 at 05:11

Hello. Does anyone know what impurities are in technical sodium molybdate dihydrate and what is percentage of sodium molybdate.

Bedlasky - 6-8-2021 at 09:58

If you have burette, you can estimate molybdate content by iodometry.

vano - 6-8-2021 at 10:42

Unfortunately I don't have

unionised - 6-8-2021 at 11:31

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.


Bedlasky - 6-8-2021 at 11:57

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]

vano - 6-8-2021 at 20:36

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!

maldi-tof - 16-8-2021 at 01:21

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.).

Bedlasky - 16-8-2021 at 01:37

Arsenic? Are you sure? I doubt that someone add something that contain arsenic in to the soil.

maldi-tof - 16-8-2021 at 03:26

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.