Tag: imperfections in solids

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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.

Multiple choice imperfections in solids solid state the solid state chemistry

Which of the following exhibit Frenkel defect?

  1. $KBr$
  2. $AgBr$
  3. $AgCl$
  4. $ZnS$
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
Explanation

$KBr, AgBr, AgCl\ and\ ZnS$ exhibit Frenkel defect.
$AgBr$ also exhibits schottky defect.
$NaCl, KCl, CsCl$ etc, exhibits schottky defect.

Multiple choice imperfections in solids solid state the solid state chemistry

Which of the following defect is seen in $FeO ?$

  1. Metal deficiency defect

  2. Metal excess defect

  3. Displacement defect

  4. Impurity defect
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$FeO$ shows metal deficiency defect. In crystal of $FeO$ some $Fe^{2+}$ cations are missing and the loss of positive charge is made up by the presence of required number of $Fe^{3+} $ ions.

Multiple choice imperfections in solids solid state the solid state chemistry

Which kind of defect is shown by the given crystal?
${ K }^{ + }$  ${ Cl }^{ - }$   ${ K }^{ + }$   ${ Cl }^{ - }$   ${ K }^{ + }$     ${ Cl }^{ - }$
${ Cl }^{ - }$  $\Box $      ${ Cl }^{ - }$    ${ K }^{ + }$   $\Box $       ${ K }^{ + }$
${ K }^{ + }$   ${ Cl }^{ - }$   $\Box $     ${ Cl }^{ - }$     ${ K }^{ + }$    ${ Cl }^{ - }$ 
${ Cl }^{ - }$   ${ K }^{ + }$   ${ Cl }^{ - }$   ${ K }^{ + }$   $\Box $        ${ K }^{ + }$   

  1. Schottky defect

  2. Frenkel defect

  3. Schottky Frenkel defects

  4. Substitution disorder
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In the given crystal equal number of cations and anions are missing (two ${K}^{+}$ and two ${Cl}^{-}$) from their normal lattice sites and the crystal maintains electrical neutrality. Hence, this is Schottky defect.

Multiple choice imperfections in solids solid state the solid state chemistry

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

  1. schottky defect

  2. frenkel defect

  3. interstitial position

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

In F-centre defect in which an anionic vacancy in a crystal is filled by one or more unpaired electron. These electron absorb light in the visible region and emits colour. So, appearance of colour in solid alkali metal halides is generally due to F-centre.

Multiple choice imperfections in solids solid state the solid state chemistry

Select the incorrect statement :

  1. Stoichiometry of crystal remains unaffected due to Schottky defect

  2. Frenkel defect usually shown by ionic compounds having low coordination number

  3. F-centres generation is responsible factor for imparting the colour to the crystal

  4. Density of crystal always increases due to substitutional impurity defect
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

(4) Density of crystal not $\uparrow$ es always it may remain constant sometimes.

Multiple choice imperfections in solids solid state the solid state chemistry

Which of the following defect is seen in $FeO$? 

  1. Metal excess defect

  2. Metal deficiency defect

  3. Displacement defect

  4. Impurity defect
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$FeO$ has metal deficiency defect. Metal deficiency defect is supposed to arise when there are lesser number of positive ions than negative ions. In case of $FeO$, the positive ions are missing from their lattice sites. 

The additional negative charge is balanced by some nearby metal ion by acquiring one more positive charge. It happens in $FeO$ because $Fe$ has capacity of showing variable oxidation states.