Why is heating of lead oxide a chemical change?
Answers
Explanation:
Chemical
Lead dioxide decomposes upon heating in air as follows:
24 PbO2 → 2 Pb12O19 + 5 O2
Pb12O19 → Pb12O17 + O2
2 Pb12O17 → 8 Pb3O4 + O2
2 Pb3O4 → 6 PbO + O2
The stoichiometry of the end product can be controlled by changing the temperature – for example, in the above reaction, the first step occurs at 290 °C, second at 350 °C, third at 375 °C and fourth at 600 °C. In addition, Pb2O3 can be obtained by decomposing PbO2 at 580–620 °C under an oxygen pressure of 1,400 atm (140 MPa). Therefore, thermal decomposition of lead dioxide is a common way of producing various lead oxides.[6]
Lead dioxide is an amphoteric compound with prevalent acidic properties. It dissolves in strong bases to form the hydroxyplumbate ion, [Pb(OH)6]2−:[2]
PbO2 + 2 NaOH + 2 H2O → Na2[Pb(OH)6]
It also reacts with basic oxides in the melt, yielding orthoplumbates M4[PbO4].
Because of the instability of its Pb4+ cation, lead dioxide reacts with hot acids, converting to the more stable Pb2+ state and liberating oxygen:[6]
2 PbO2 + 2 H2SO4 → 2 PbSO4 + 2 H2O + O2
2 PbO2 + 4 HNO3 → 2 Pb(NO3)2 + 2 H2O + O2
PbO2 + 4 HCl → PbCl2 + 2 H2O + Cl2
However these reactions are slow.
Lead dioxide is well known for being a good oxidizing agent, with an example reactions listed below:[7]
2 MnSO4 + 5 PbO2 + 6 HNO3 → 2 HMnO4 + 2 PbSO4 + 3 Pb(NO3)2 + 2 H2O
2 Cr(OH)3 + 10 KOH + 3 PbO2 → 2 K2CrO4 + 3 K2PbO2 + 8 H2O