Single Choice

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

Asublimes
Bmelts
Cforms a non-stoichiometric compound at high temperatures
Correct Answer
Dall of the above

Solution

Zinc oxide is white in colour at room temperature. On heating, it loses oxygen and turns yellow.
$$ZnO \,\,\, \underrightarrow{ \text{Heating} } \,\, { Zn }^{ 2+ }+\dfrac { 1 }{ 2 } { O }_{ 2 }+2{ e }^{ - }$$
Now, there is an excess of zinc in the crystal and its formula becomes $$Zn_{1+x}O$$. The excess $$Zn^{2+}$$ ions move to the interstitial sites and the electrons to the neighbouring interstitial sites. This gives rise to colour.
Hence, $$ZnO$$ is white when cold and yellow when hot because it forms a non-stoichiometric compound at high temperatures.

SIMILAR QUESTIONS

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

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:

Solid State

Select the correct statement regarding F-centre.

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