[telle_star]

Hey all,
I was just wondering if anyone would know the complete balanced equation between crocoite and HCl to make chromium oxide? A reference would be helpful to since i can find the reaction anywhere.
I got an idea...
PbCr04 + HCl ---> CrO3 + ??
Please *delete me*
Thanks

[madscientist]

In the mid 18th century analysis of Siberian "red lead" (PbCrO4, crocoite) from Siberia showed that it contained quite a lot of lead, but also a further material. This was eventually identified as chromium oxide. Chromium oxide was discovered in 1797 by Louis-Nicholas Vauquelin, who prepared the metal itself in the following year. Starting from crocoite the procedure was to powder the mineral and to precipitate the lead out through its reaction with hydrochloric acid (HCl in water). The residue was chromium oxide, CrO3. Heating this oxide in an oven in the presence of charcoal as a reducing agent gave the metal itself.

http://www.webelements.com/webelements/elements/text/Cr/hist.html

Have a good read of the above quote, it should tell you how you need to write out your reaction, think about what happens, what species are/is produced in the precipitation reaction with lead and HCl.

cheers,

madscientist :albert:

[jen]

I asked my teacher and this's an answer question
PbCrO4 + HCl ---> CrO3 + Cl2  + PbCl2 + H2O  

[Borek]

I asked my teacher and this's an answer question
PbCrO4 + HCl ---> CrO3 + Cl2  + PbCl2 + H2O  

No way this can be balanced. Cl^- gets oxidized to Cl₂, but there is no reducing agent.

[Alberto_Kravina]

I think that a possible reation could be:

PbCrO₄ + 2 HCl ----> PbCl_2(s) + "H₂CrO₄"

And maybe this instable chromic acid could decompose to CrO₃ and H₂O

I'm not sure if this reaction happens, though.
I'm not sure....maybe if Excess HCl is added dichromate could form...

[Negahrebas]

2CrO₄^2- + 2H¹⁺ = Cr₂O₇^2- + H₂O

==>

2PbCrO₄ + 2HCl = PbCr₂O₇ + PbCl₂ + H₂O