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Cinnabar (HgS) and galena (PbS) on roast...

Cinnabar `(HgS)` and galena `(PbS)` on roasting often yield their respective metals but zinc blende (ZnS) does not. Explain with reason.

Text Solution

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When cinnabar and galena are roasted, they are partly converted into their respective oxides. Oxides of mercury and lead are unstable while that of zinc is stable. Therefore, oxides of Hg and Pb reduce their sulphides to the corresponding metals. However, `ZnS` is not reduced to Zn by `ZnO.`
`HgS+underset("(unstable)")(2HgO)overset(Delta)rarr 3Hg +SO_(2)uarr, PbS +underset("(unstable)")(2PbO) overset(Delta)rarr 3Pb+SO_(2)uarr,`
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