Tag: imperfections in solids

Questions Related to imperfections in solids

The anionic sites occupied by unpaired electrons are called F-centers or colour centers. They impart ______ $(X)$ colour to the crystals on $NaCl.$ Excess of lithium makes $LiCl$ crystals ______ $(Y)$ and excess of potassium makes $KCl$ crystals ______ $(Z)$. $(X)$, $(Y)$ and $(Z)$ are:

chemistry solid state imperfections in solids

  1. yellow, green and pink respectively.

  2. pink, yellow and violet (or lilac) respectively.

  3. yellow, pink and violet (or lilac) respectively.

  4. red, yellow and pink respectively,

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Correct Option: C
Explanation:

$NaCl$ shows the metal excess defect, which results in the formation of an F-center in the crystal. When light falls on this crystal, the electron in F-center gets excited. This F-center is then responsible for the yellow $(X)$ color of $NaCl$.

In a similar way, the excess of lithium imparts Pink $(Y)$ colour of $LiCl$ crystals.
In a similar way, the excess of potassium imparts violet/lilac $(Z)$ colour of $KCl$ crystals.

$F-$centres are :

chemistry solid state imperfections in solids

  1. the electrons trapped in anionic vacancies

  2. the electron trapped in cationic vacancies

  3. non-equivalent sites of stoichiometric compound

  4. All of the above

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Correct Option: A
Explanation:

$F$-centres or colour centres are points in a crystalline compound at which negative ion missing is replaced by one or more unpaired electrons. 


Hence, they are electrons trapped in anionic vacancies.

Therefore, the option is A.

The incorrect statement is :

chemistry solid state imperfections in solids

  1. When crystals of NaCI are heated in an atmosphere of sodium vapour, it appears yellow due to F-centres.

  2. $ O _2 $ is paramagnetic , $ CrO _2 $ is Ferromagnetic and $ MnO $ is anti-Ferromagnetic

  3. Certain oxides $ VO, VO _2VO _3 $ and $ TiO _3 $ show metallic properties at all temperatures.

  4. CCP & HCP have same coordination number.

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Correct Option: C

The correct statement regarding $F-$centre is:

chemistry solid state imperfections in solids

  1. electron are held in the voids of crystals

  2. $F-$centre produces colour to the crystals

  3. conductivity of the crystal increases due to $F-$centre

  4. all of the above

Show answer
Correct Option: D
Explanation:

$F-$ centre is a type of crystallographic defect in which an anionic vacancy in a crystal is filled by one or more unpaired electron, depending on the charge of the missing ion in the crystal. These unpaired electrons produces colour in the crystal by absorbing light in the visible spectrum. The unpaired electron acts as charge carriers and hence the crystal conducts electricity.

The presence of excess sodium in sodium chloride makes the crystal appearance yellow. This is due to the presence of

chemistry solid state imperfections in solids

  1. Schottky defect

  2. Frenkel defect

  3. F-centres

  4. Interstitial defects

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Correct Option: C

Each of the following statement is correct except

chemistry solid state imperfections in solids

  1. the lattice positions left vacant by anion and occupied by electrons are called F-centres

  2. the presence of F-centres makes the lattice electrically neutral and diamagnetic

  3. the presence of F-centres gives colour to the crystals

  4. F-centres contain unpaired electrons

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Correct Option: B

In feldspar and zeolite, $Si^{4+}$ ions are replaced by which ions?

chemistry solid state imperfections in solids

  1. Oxide ion

  2. Hydroxide ion

  3. Aluminium ion

  4. Potassium ion

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Correct Option: C
Explanation:

Generally, the ion exchange tendency of a material depends on the extent of isomorphous substitution in the tetrahedral framework. Thus, the $Si^{4+}$ ions of feldspar and zeolite are replaced by $Al^{3+}$ (aluminium ion).

ZnO shows yellow colour on Heating due to:

chemistry solid state imperfections in solids

  1. d-d transition

  2. C-T spectra

  3. Higher polarisation caused by $Zn^{2+}$ ion

  4. F-centres

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Correct Option: D
Explanation:

$ZnO$ shows yellow colour of heating due to F-centre

$ZnO\longrightarrow Zn^{2+}+2e^-+\cfrac{1}{2}O _2$
Electron get trapped in anion sites. This is called as F-centre. Due to F-centre colour of many compounds occurs.

Interstitial compounds are formed when small atoms are trapped inside the crystal lattice of
metals. Which of the following is not the characteristic property of interstitial compounds?

chemistry d and f block elements imperfections in solids solid solutions formation of complex compounds and constituent of catalysts general characteristics of first transition series

  1. They have high melting points in comparison to pure metals.

  2. They are very hard.

  3. They retain metallic conductivity.

  4. They are chemically very reactive.

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Correct Option: D
Explanation:
Interstitial compounds have high melting points in comparison to pure metals. They are very hard and retain metallic conductivity. They are chemically inert i.e. not reactive.

Which of the following is an interstital compound ?

chemistry d and f block elements imperfections in solids solid solutions formation of complex compounds and constituent of catalysts general characteristics of first transition series

  1. $ PdCI _2 $

  2. $ NH _3 $

  3. $ ZnO$

  4. $ TiH $

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Correct Option: A