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The Solid State — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryThe Solid State2 Marks
Question
Why does white $\mathrm{ZnO}(\mathrm{s})$ becomes yellow upon heating?
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Answer

On heating ZnO loses oxygen according to the following reaction.
$\text{ZnO}\rightarrow\text{Zn}^{2+}+\frac{1}{2}\text{O}_2+2\text{e}^1$
$\mathrm{Zn}^{2+}$ ions and electrons move to interstitial sites and F -centres are created which impart yellow colour to $\mathrm{ZnO}(\mathrm{s})$.

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