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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.

Multiple choice imperfections in solids solid state the solid state chemistry

In a crystal, at $827^{\circ}C$, one out of $10^{10}$ lattice site is found to be vacant, while in the same solid, one out of $2 \times 10^9$ lattice site is found to be vacant at $927^{\circ}C$. What is the enthalpy of vacancy formation in kJ/mol unit?

  1. $76.8$
  2. $176.8$
  3. $33$
  4. $23$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\cfrac {^nV}{N}=Ae^{-\Delta H _V/RT} \longrightarrow (x)$

$\left(\cfrac {^nV}{N}\right) _{827^oC}=\cfrac {1}{10^{10}} \longrightarrow (1)$
$\left(\cfrac {^nV}{N}\right) _{927^oC}= \cfrac {1}{2 \times 10^9} \longrightarrow (2)$                                   $\therefore T _1= 827+273=1100K ; T _2=927+273=1200K$

$\Rightarrow \cfrac {(2)}{(1)}= \cfrac {1/2\times 10^9}{1/10^{10}}= \cfrac {10^ {10}}{2 \times 10^9}= 0.5 \times 10=5$
$x \Rightarrow 2.303 \log 5= - \cfrac {\Delta H _V}{R} \left(\cfrac {1}{T _1}-\cfrac {1}{T _2}\right)$
$\therefore \Delta H _V= 2.303 \times \log 5 \times 8.314 \times \left(\cfrac {1100\times 1200}{100}\right)$
               $=1.766 \times 10^5 J$
               $=176.6kJ/mol$ $unit$ .

Multiple choice imperfections in solids solid state the solid state chemistry

Calcium crystallizes in a face centred cubic unit cell with a $=0.556$ nm. Calculate the density if it contains:

(i) $0.1\%$ Frenkel defect
(ii) $0.1\%$ Schottky defect

  1. $1.546, 1.546$
  2. $1.546, 1.544$
  3. $15.46, 15.46$
  4. $21.76, 41.66$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$1.$ In frenkel defect there is no change in original density

$\rho=\cfrac{Z\times M _A}{N _A\times a^3}$
$\implies \rho=\cfrac{4\times 40}{6.023\times 10^{23}\times 171.8\times 10^{-24}}$
$\implies \rho=1.546$ $g/cm^3$

$2.$ In schottky defect $Z _{eff}$ changes so density changes
$Z _{new}=4-\cfrac{4\times 0.1}{100}=3.996$
$\rho =\cfrac { Z\times M _{ A } }{ N _{ A }\times a^{ 3 } } $
$\implies \rho =\cfrac { 3.996\times 40 }{ 6.023\times 10^{ 23 }\times 171.8\times 10^{ -24 } } $
$\implies \rho =1.544$$g/cm^{ 3 }$

Multiple choice imperfections in solids solid state the solid state chemistry

Statement 1: KCl is more likely to show schottky defect while Lil is more likely to show Frenkel defect.
Statement 2: Schottky defect is more likely in ionic solids in which cations and anions are of comparable size while Frenkel defect is more likely is which cations and anions have large differences in their ionic sizes.

  1. Statement-1 is true, Statement-2 is true and Statement-2 is correct explanation for Statement-1

  2. Statement-1 is true, Statement-2 is true and Statement-2 is not the correct explanation for Statement-1

  3. Statement-1 is true but Statement-2 is false

  4. Statement-1 is false but Statement-2 is true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In case of KCl, the cation and the anion are of comparable size while in case of LiI, the cation Li+ is very small as compared to the iodide ion, I-. Hence, KCl is more likely to show Schottky defect while LiI tends to show Frenkel defect. Thus, the statements 1 and 2 are true and 2 is correct explanation of 1.