Single Choice

Zinc oxide loses oxygen on heating according to the reaction. $$ZnO\xrightarrow { heat } Zn^ { 2+} +\frac { 1 }{ 2 } O_ 2+2e^-$$ It becomes yellow on heating because:

A$$Zn^{2+}$$ ions and electrons move to interstitial sites and F-centers are created
Correct Answer
Boxygen and electrons move out of the crystal and ions become yellow
C$$Zn^{2+}$$ again combine with oxygen to give yellow oxide.
D$$Zn^{2+}$$ are replaced by oxygen.

Solution

$$ZnO$$ shows non-stoichiometric defect under metal excess defect. When $$ZnO$$ is heated it loses oxygen as: $$ZnO \xrightarrow {\triangle} Zn^{2+} + \cfrac 12 O_2 + 2e^-$$ The $$Zn^{2+}$$ and the two electrons formed move to interstitial sites of crystal. The electrons trapped in the interstitial sites are less tightly bound and gets promoted by absorption of photons in the violet region. So, we see the complementary color to violet which is yellow. Hence, Option "A" is the correct answer.

SIMILAR QUESTIONS

Solid State

ZnO is white when cold and yellow when hot because it____.

Solid State

The appearance of colour in solid alkali metal halides is generally due to:

Solid State

Which of the following statements is/are correct ?

Solid State

Select the correct statement(s) regarding defects in solids:

Solid State

$$ZnO$$ is white when cold and yellow when heated. It is due to development of:

Solid State

Analysis shows that nickel oxide has the formula $$Ni_{0.98}O_{1.00}$$. What fractions of nickel exist as $$Ni^{2+}$$ and $$Ni^{3+}$$ ions?

Solid State

Select the correct statement regarding F-centre.

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