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I have heated lead(II) oxide at about 450 °C and it changed to lead(II,IV) oxide, but as soon as I took it out from hot plate, it changed to $\ce{PbO}$ again. Why does it happen? Is there a better way to synthesize $\ce{Pb3O4}$ from $\ce{PbO}?$

I had the same problem when I wanted to change $\ce{Pb3O4}$ to $\ce{PbO}.$ When I heated $\ce{Pb3O4},$ it got dark. When I took it out, it became red again. I used straight flame to decompose it.

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    $\begingroup$ It seems the cooling down is not fast enough to freeze the equilibrium, previously reached at high temperature. $\endgroup$
    – Poutnik
    May 1 at 13:16
  • $\begingroup$ how can I cool it down very fast? is there any tool? $\endgroup$
    – Nima
    May 1 at 13:29
  • $\begingroup$ I wonder that when Pb3O4 is made, it won't change to PbO unless it is heated around 600°C so how does it come back to PbO!!!? $\endgroup$
    – Nima
    May 1 at 13:32
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    $\begingroup$ Color can be deceiving. Better would by gravimetric analysis. $\endgroup$
    – Poutnik
    May 1 at 13:37
  • $\begingroup$ will it be better if I make PbCO3 and heat it? or it will treat the same? $\endgroup$
    – Nima
    May 1 at 14:23

1 Answer 1

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Heat is very different while conducting such type of reactions because at a specific range of temperature, you will get a different species of lead oxide. The general scheme of lead oxide conversion is as follows:

$$\ce{PbO2 ->[\pu{293 ^\circ C}] Pb12O19 ->[\pu{351 ^\circ C}] Pb12O17 ->[\pu{375 ^\circ C}] Pb3O4 ->[\pu{605 ^\circ C}] PbO}$$

So, around 375 °C-450 °C, you will get lead(II,IV) oxide. As soon as you overshoot the temperature, it will convert to lead(II) oxide.

If you have lead(IV) oxide, then it can be converted to lead(II,IV) oxide at around 450 °C-480 °C but if you overshoot it, lead(II,IV) oxide will decompose back to lead(IV) oxide (reaction completes at 580 °C). Wikipedia took the reaction from Lead Compounds by Dodd S. Carr, 2000

$$ \begin{align} \ce{6PbO + O2 &->[\pu{450 ^\circ C - 480 ^\circ C}] Pb + CO2}\\ \ce{2 Pb3O4 &->[>500 ^\circ C] 6PbO + O2} \end{align} $$

Lead(II,IV) oxide is relatively stable to atmospheric oxidation and insoluble in water and as such, it was used as a pigment for a long time until it was scraped off due to its toxicity. It is temperature resistant upto a certain point.

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  • $\begingroup$ I control the temperature during the process by using a laser thermometer it never gets more than 470°c but when the temperature gets 300°c and less, it changes to yellow again $\endgroup$
    – Nima
    May 25 at 13:30
  • $\begingroup$ as soon as temperature gets 470°c the color gets red and when it gets 300°c the color gets yellow!!! $\endgroup$
    – Nima
    May 25 at 13:31

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