Tag: imperfections in solids

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Multiple choice chemistry solid state 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:

  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,
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

Multiple choice chemistry solid state imperfections in solids

$F-$centres are :

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

Multiple choice chemistry solid state imperfections in solids

The incorrect statement is :

  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.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The statement regarding VO, VO2, VO3, and TiO3 is incorrect because these oxides show metallic or insulating properties depending on the temperature, rather than metallic properties at all temperatures. The other statements correctly describe F-centres, magnetic properties, and close-packing structures.

Multiple choice chemistry solid state imperfections in solids

The correct statement regarding $F-$centre is:

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

Multiple choice chemistry solid state imperfections in solids

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

  1. Schottky defect

  2. Frenkel defect

  3. F-centres

  4. Interstitial defects
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When NaCl crystals are heated in sodium vapor, sodium atoms deposit on the surface and chloride ions diffuse to the surface to form NaCl. The remaining electrons occupy the anionic vacancies, creating F-centres, which absorb light and impart a yellow color.

Multiple choice chemistry solid state imperfections in solids

Each of the following statement is correct except

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

F-centres contain unpaired electrons, which makes the crystal paramagnetic, not diamagnetic. The other statements are correct descriptions of F-centres.

Multiple choice chemistry solid state imperfections in solids

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

  1. Oxide ion

  2. Hydroxide ion

  3. Aluminium ion

  4. Potassium ion
Reveal answer Fill a bubble to check yourself
C Correct answer
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).

Multiple choice chemistry solid state imperfections in solids

ZnO shows yellow colour on Heating due to:

  1. d-d transition

  2. C-T spectra
  3. Higher polarisation caused by $Zn^{2+}$ ion

  4. F-centres
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

Multiple choice 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

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?

  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.
Reveal answer Fill a bubble to check yourself
D Correct answer
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.
Multiple choice 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

Which of the following is an interstital compound ?

  1. $ PdCI _2 $
  2. $ NH _3 $
  3. $ ZnO$
  4. $ TiH $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Interstitial compounds are formed when small atoms like hydrogen, carbon, or nitrogen are trapped in the crystal lattices of transition metals. Titanium hydride (TiH) is a classic example of a non-stoichiometric interstitial hydride.