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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Muonium on August 24, 2018, 09:51:20 PM

Title: White Molybdenum precipitate from reaction with sodium bicarbonate
Post by: Muonium on August 24, 2018, 09:51:20 PM

Hi everyone!

I dissolved a small amount of Molybdenum powder in 31.45% hydrochloric acid/water (50/50). I then buffered the solution with sodium bicarbonate and white precipitate form. I initially thought it was a Molybdenum carbonate, but I can't find anything on it, despite having searched a lot.

Even dry, the precipitate is all white. This eliminates MoO3, and Sodium molybdate since it have a great solubility in aqueous solutions.

If somebody know anything on this, please let me know.

Thanks a lot!

Title: Re: White Molybdenum precipitate
Post by: chenbeier on August 25, 2018, 11:13:18 AM

One property of molybdenum is, it is unsulouble in non oxidising acids like hydrochloric acid.
So your metall wasnt mlybdenum or maybe alloy of it. Maybe you have titanium what forms white TiO₂

Title: Re: White Molybdenum precipitate
Post by: Mitch on August 28, 2018, 12:09:31 PM

Molybdenum chloride is soluble in water, molybdenum carbonate is not. Only alkali carbonates are soluble in water. Reviewing your solubility rules could help.

@chenbeier, perhaps it was a salt of molybdenum?

Title: Re: White Molybdenum precipitate from reaction with sodium bicarbonate
Post by: Muonium on September 03, 2018, 03:41:58 PM

It's true Molybdenum isn't supposed to dissolve in HCl, so my sample was probably impure. I know most carbonates are insoluble, but I couldn't find any information on the existence of a Molybdenum carbonate.

The sample was the leftover powder stuck inside the bag of the 99.9% Molybdenum powder I bought. I poured the HCl/water directly on the bag to leach it. Because of this I couldn't see the difference between before and after the leaching: the bag looked the same with the same amount of stuck powder.

Let's say the impurity that dissolved was mostly Titanium, would it precipitate the dioxide when buffered with Sodium bicarbonate?

Thanks everyone

Title: Re: White Molybdenum precipitate from reaction with sodium bicarbonate
Post by: chenbeier on September 03, 2018, 04:04:21 PM

Yes that would work. Maybe you have possibilty to do an EDX or RFA on your powder, to get the elements inside.

Title: Re: White Molybdenum precipitate from reaction with sodium bicarbonate
Post by: Muonium on September 03, 2018, 06:09:54 PM

@chenbeier, what would work?? I don't have such equipments, I'm an amateur chemist. The only thing I will be able to perform is neutron activation analysis on compounds when my irradiator will be completed. Meanwhile I just can't analyze unknown precipitates, only with basic qualitative analysis.

Thanks

Title: Re: White Molybdenum precipitate from reaction with sodium bicarbonate
Post by: chenbeier on September 04, 2018, 05:16:46 AM

The precipitation of Titanium dioxide.

Title: Re: White Molybdenum precipitate from reaction with sodium bicarbonate
Post by: Muonium on September 05, 2018, 05:17:37 PM

I think the impurity is not necessarily Titanium, I will have to do trials and errors.

Thank you