Sciencemadness Discussion Board

red lead (2PbO*PbO2)

Magpie - 10-10-2015 at 13:55

I recently made this compound, also sometimes designated Pb3O4, using PbO. About 4g was placed on an inverted ceramic lid in a muffle furnace. This was heated for 6 hours at 465±10°C. About every half hour I would turn the powder with a spatula. The temperature range shown in Wiki was 450-480°C, the rest of the procedure was based on that found in"Synthetic Inorganic Chemistry," p.281, by Blanchard et al in the forum library.

The color changes indicated in Blanchard occured as described. But there was no weight increase. From this equation I calculated that there should be about a 2% weight increase:

3PbO + 1/2O2 --> 2PbO*PbO2

The final product is shown below.

Has anyone else made red lead? If so, what was your experience?

red lead.jpg - 68kB

CharlieA - 10-10-2015 at 17:03

Neat prep, Magpie! What is the precision/accuracy of your weighing (I know, "massing", BUT I'm too old to change my habits)? 2% of 4g is only 80 mg, and I wonder if there were other losses (spattering?) to account for no gain in weight. I'm just starting to set up a lab after 35 years of no chemistry activity, so I've got a lot to learn (and re-learn!). :) CharlieA

Magpie - 10-10-2015 at 17:34

I used my gun powder scale which weighs down to 0.1 grain (7mg). The wt increase was only 0.1 grain, or 7 mg.

The color change was interesting in that the orange PbO went to a dark brown right away on heating. On cooling it changed to red. What you see in the photo is fairly close.

Kagutsuchi - 10-10-2015 at 23:03

I am planning to perform it, too, but I must be really careful because my PbO is contamined withquite a lot of Pb(NO3)2, so I must heat it before the experiment.

unionised - 11-10-2015 at 03:43

If there was 2% water (and maybe CO2) absorbed in the PbO then there would be no overall change in mass.

gsd - 11-10-2015 at 07:31

Hi Magpie! Nice preparation.
Just a thought, for 3 mole of PbO, it needs 1 atom of O for this reaction as your equation shows.
Hence Oxygen (O) required is 4*16/(3*223.2) = 0.09558gm = 1.08 lit of O2 @ NTP. Which corresponds to 1.08/0.21 = 5.1 lit of air.
Now your temperature was 465 Deg C avg. which corresponds to required air volume of 5.1*(273+465)/273=13.8 lit. This much air is required if you have a perfect mixing. Barring some "turning over" in-between, yours was a stagnant system.

Are you sure enough Oxygen was contacted with your PbO?. Normally this types of preparations are done in a flow system.


[Edited on 11-10-2015 by gsd]

Magpie - 11-10-2015 at 09:34

Hi gsd. I only used about 4g of PbO. Also, every half hour I was opening the furnace and stirring the powder. So I think it was getting enough oxygen.

Unionised's hypothesis is more likely correct. For cooling the hot red lead I placed it in a dessicator. What I should have done was dry the PbO at 120°C or so before weighing and firing.

Squall181 - 12-10-2015 at 04:58

I've attempted to make red lead in the past and had some success, but my only real test at the time was using it to make some crackling stars. I used my hot plate to heat lead carbonate with constant agitation until it turned red.

Here's a video of the whole process if anyone is interested.