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Multiple choice imperfections in solids solid state the solid state chemistry

Select the correct statement regarding F-centre.

  1. Electrons are held in the voids of crystals.

  2. F-centre imparts colour to the crystal.

  3. Conductivity of the crystal increases due to F-centre.

  4. All the above.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When Potassium chloride is heated in sodium vapour, we see that is acquires a yellow colour. The heating in excess sodium creates new lattice sites for sodium. To maintain the structure, an equal number of chloride sites are also created but the latter are vacant. The electron of the potassium atom that is ionized in the KCl matrix is trapped by the chloride ion vacancy. This trapped electron can be freed into the crystal by absorbing visible light and hence, the colour. A trapped electron at an anion vacancy is an electronic defect and it is known as F-centre.

Multiple choice imperfections in solids solid state the solid state chemistry

Frenkel defect is found in crystals in which the radius ratio is:

  1. low
  2. $1.3$
  3. $1.5$

  4. slightly less than unity
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Frenkel defect is exhibited in ionic compounds in which the radius ratio is low. The cations and anions differ much in their sizes and the ions have low co-ordination numbers. However, in Schottky defect the size of cation and anion

are almost same, ex- KCl, AgBr.
Hence, the correct option is $\text{A}$

Multiple choice imperfections in solids solid state the solid state chemistry

An ionic solid has some point defect but its experimental density is equal to its theoretical density. The type of defect is:

  1. Schottky defect

  2. Frenkel effect

  3. Metal excess defect

  4. Metal deficient defect
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
An ionic solid has some point defect but its experimental density is equal to its theoretical density. The type of defect is Frenkel effect.

When an ion leaves its correct lattice site and occupies an interstitial site, Frenkel defect is observed. Hence, the density of crystal is not affected.

In Schottky defect, the density of the crystal decreases.
Multiple choice imperfections in solids solid state the solid state chemistry

Ionic solids with Schottky defects contain in their structure

  1. equal number of cations and anions vacancies

  2. interstitial anions and anion vacancies

  3. cation vacancies only

  4. cation vacancies and interstitial cations
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Schottky defect is the defect which is produced when one cation and anion is missing from their respective positions leaving behind a pair of holes. The crystal as a whole remains neutral because the number of missing positive ions (cations) and negative ions (anions) is the same.

Multiple choice imperfections in solids solid state the solid state chemistry

In a solid lattice, the cation has left a lattice site and is located at an interstitial position. The lattice defect is known as____________.

  1. Interstitial defect

  2. Valency defect

  3. Frenkel defect

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

Frenkel defect is a defect which is created when an ion leaves its appropriate site in the lattice and occupies an interstitial site. A hole or vacancy is thus produced in the lattice.
The electroneutrality of the crystal is maintained since the number of positive and negative ions is the same. Since positive ions are small in size, they usually leave their positions in the lattice and occupy interstitial positions.

Multiple choice imperfections in solids solid state the solid state chemistry

Schottky defect is noticed in:

  1. $NaCl$
  2. $KCl$
  3. $BeCl _2$
  4. both $A$ and $B$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

All alkali metal halides show the Schottky defect due to the formation of excess cations.
Thus Schottky defect will be noticed in $NaCl \; & \; KCl$.
Thus, option $(D)$ is right answer.

Multiple choice imperfections in solids solid state the solid state chemistry

What type of crystal defect is indicated in the diagram below?

$Na^{+}$ $Cl^{-}$ $Na^{+}$ $Cl^{-}$ $Na^{+}$ $Cl^{-}$
$Cl^{-}$ $Cl^{-}$ $Na^{+}$ $Na^{+}$
$Na^{+}$ $Cl^{-}$ $Cl^{-}$ $Na^{+}$ $Cl^{-}$
$Cl^{-}$ $Na^{+}$ $Cl^{-}$ $Na^{+}$ $Na^{+}$

  1. Frenkel defect

  2. Schottky defect

  3. Interstitial defect

  4. Frenkel and Schottky defects
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Schottky defect is indicated in the diagram as equal number of sodium cation and chloride anion are missing.
In Frenkel defect, a cation or anion leaves its regular site and occupies interstitial position.

Multiple choice imperfections in solids solid state the solid state chemistry

Which of the following is/are correct about the point defects?

  1. In Frenkel defect, the dielectric constant of solid increases

  2. In Schottky defect, the density of solid decreases

  3. In Frenkel defect, the density of solid decreases

  4. In Shcottky defect, the dielectric constant of solid increases
Reveal answer Fill a bubble to check yourself
A,B Correct answer
Explanation

(A) Frenkel defect tends to increase the dielectric constant of the crystal because of presence of the ions in interstitial sites.


(B) In Schottky defects an equal number of cations and anions are missing from the interstitial sites and form vacancy or hole and thus density decreases due to these missing cation and anions.

(C) In Frenkel defect in which an tom is displaced from its' lattice position to an interstitial site creating a vacancy at the original site and interstitial defect at the new location. The density do not change as it involves only migration of ions within the crystals preserving both volume and mass.

(D) In Schottky defect dielectric constant of solid do not change.

Answer: $A,B$

Multiple choice imperfections in solids solid state the solid state chemistry

A solid solution of $CdBr _{2}$ in $AgBr$ contains:

  1. schottky defects

  2. frenkel defects

  3. colour centres

  4. frenkel as well as schottky defects
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Frenkel Defect: This defect is shown by ionic solids. The smaller ion is dislocated from its normal site to an interstitial site. Frenkel defect is shown by ionic substance in which there is a large difference in the size of ions.


Schottky Defect: It is basically a vacancy defect in ionic solids. In order to maintain electrical neutrality, the number of missing cations and anions are equal. Schottky defect is shown by ionic substances in which the cation and anion are of almost similar sizes.

The radius ratio for CdBr2 and AgBr is intermediate. Thus, it shows both frenkel and schottky defects.