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My inorganic textbook says

Cupellation is a process, where crude gold is taken in a small bowl called cupell and melted in the presence of air. Due to high oxygen affinity of Pb, it is converted to PbO(volatile) and escapes from the system

Now, the affinity for sulphur and lead is explained by HSAB(soft acid-soft base). But how to account for the affinity of oxygen (hard base)and lead (soft acid) ?

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    $\begingroup$ More important is general resistance of noble metals to oxidation. $\endgroup$ – Mithoron Dec 3 '18 at 23:06
  • $\begingroup$ @Mithoron Yes that is true, but noble metals generally resist reacting with most elements, don't they? While I have looked thorough a few books about cupellation,and they all talk about lead's affinity for oxygen, and I'm not quite sure about the rationale for this. $\endgroup$ – YUSUF HASAN Dec 4 '18 at 3:12

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