Question

Zno on heating turns yellow and becomes white when cold?? explain ncery 2

Answer 1

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ZnO shown non stoichiometric defect under metal excess defect. When zinc oxide is heated it become yellow because on heating it loses oxygen because of which f-centers are generated which give yellow colour

Answer 2

Answer:

Zno on heating turns yellow and becomes white when cold because When colourless ZnO is strongly heated, the metal atoms are deposited on crystal surface and anions 0^2- migrate to the surface producing vacancies at anion lattice points.

These anions combine with Zn atoms forming ZnO and rclease clectrons.

Zn+O^2- ---------> ZnO+2e^-

These released electrons diffuse into the crystal and occupy vacant sites of anions and produce F- centres. Due to these colour centres, ZnO turns yellow.