a) ZnO exhibits enhanced electrical conductivity on heating.why? b) Potassium chloride somestimes gets violet instead of pure white.why? plz rply as soon as possible
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Both ZnO and KCl exhibit colour due to non-stoichiometric metal defects
1) Zinc oxide is white in colour at room temperature. On heating it loses oxygen and turns yellow
Now there is excess of zinc in the crystal. The excess Zn ions move to interstitial sites and the electrons to neighbouring interstitial sites. Thus due to presence of these interstitial electrons ZnO turns yellow and exhibits enhanced electrical conductivity.
2) KCl sometimes displays violet colour also due to metal effect defects. However, in case of KCl the excess of metal is due to anionic vacancies. In such crystals, the anionic sites are occupied by unpaired electrons and these sites are called F-centres. The colour results by excitation of these electrons when they absorb energy from the visible light falling on the crystals.
1) Zinc oxide is white in colour at room temperature. On heating it loses oxygen and turns yellow
Now there is excess of zinc in the crystal. The excess Zn ions move to interstitial sites and the electrons to neighbouring interstitial sites. Thus due to presence of these interstitial electrons ZnO turns yellow and exhibits enhanced electrical conductivity.
2) KCl sometimes displays violet colour also due to metal effect defects. However, in case of KCl the excess of metal is due to anionic vacancies. In such crystals, the anionic sites are occupied by unpaired electrons and these sites are called F-centres. The colour results by excitation of these electrons when they absorb energy from the visible light falling on the crystals.
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