Tag: imperfections in solids

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Multiple choice imperfections in solids solid state the solid state chemistry

The type of defect in $Nacl$ crystal will be -

  1. point defect

  2. interstitial will be

  3. vacancy defect

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

NaCl is an ionic crystal that typically exhibits Schottky defects, which are a type of vacancy defect where ions are missing from their lattice sites.

Multiple choice imperfections in solids solid state the solid state chemistry

If 1 mole of NaCl is doped with $10^{-3}$ mole of $SrCl _2$. What is the number of cationic  vacancies per mole of NaCl ?

  1. $10^{-3}\, mole ^{-1}$
  2. $6.02\times 10^{18}\, mole ^{-1}$
  3. $10^{50}\, mole ^{-1}$
  4. $6.02\times 10^{20}\, mole ^{-1}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When NaCl is doped with SrCl2, each Sr2+ ion replaces two Na+ ions to maintain electrical neutrality, creating one cationic vacancy per Sr2+ ion added. Thus, 10^-3 mole of SrCl2 introduces 10^-3 moles of cationic vacancies, which when multiplied by Avogadro's number gives 6.02 x 10^20 per mole.

Multiple choice imperfections in solids solid state the solid state chemistry

An excess of potassium ions makes KCl crystals appear violet or Lilac in colour since

  1. some of the anionic sites are occupied by an unpaired electron

  2. some of the anionic sites are occupied by a pair of electrons

  3. there are vacancies at someanionic sites

  4. F-centres are created which impart colour to the crystals
Reveal answer Fill a bubble to check yourself
A,D Correct answer
Explanation

When KC1 is heated in vapour of K, some of the Cl leave their lattice site and create anion vacancies. This chloride ion wants to combine with K vapour to form potassium chloride. For doing so K atom loses electrons form K ions. This released electron diffuses into the crystal to get entrapped in the anion vacancy called F-centre. When visible light falls on the crystal, this entrapped electron gains energy, goes to the higher level when it comes back to the ground state, energy is released in the form of light.

Multiple choice imperfections in solids solid state the solid state chemistry

If $NaCl$ is doped with $10^{-3}$ mol$\%$ of $SrCl _2$, the concentration of cation vacancies will be: 

$(N _A=6.02\times 10^{23}mol^{-1}$)

  1. $6.02\times 10^{15} mol^{-1}$
  2. $6.02\times 10^{16} mol^{-1}$
  3. $6.02\times 10^{18} mol^{-1}$
  4. $6.02\times 10^{14} mol^{-1}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given that $1$ $mol$ of $NaCl$ is doped with $\cfrac{10^{-3}}{100}$ $mol$ of $Sr^{+2}=10^{-5}$ $mol$


Cation vacancies produced by $Sr^{2+}$ ion $=1$               [$\because$ 1 $Sr^{+2}$ can replace 2 $Na^+$]


So, concentration of cation vacancies produced by $10^{-5}$ mole of $SrCl _2$

$=6.023\times 10^{23}\times 10^{-5}$

$=6.023\times 10^{18}$ per mole

Multiple choice imperfections in solids solid state the solid state chemistry

$KBr$ shows, which of the following defects?

  1. Frenkel defect

  2. Schottky defect

  3. Metal excess defect

  4. Metal deficiency
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Schottky defect is shown in highly ionic compound, highly coordinated compounds, and where there is only a small difference in sizes of cations and anions of which the compound lattice is composed.

Examples:- $NaCl, KCl, KBr, CsCl, AgBr$

Multiple choice imperfections in solids solid state the solid state chemistry

In a non-stochiometric sample of cuprons sulphide, with the composition $Cu _{1.8}$, cupric ions are also present in the lattice. The mole % of $Cu^{2+}$ present in the copper content of the crystal is:

  1. $99.9$%
  2. $11.11$%
  3. $88.88$%
  4. $18$%
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$180 \ Cu$ atoms are associated with $100 \ S$ atoms.

Let $x$ atoms be present as $Cu^{+}$
Total charge on $xCu^+$ and $(180-x)Cu^{2+}$ must be equal to total charge on $100 \ S^{2-}$ ions.
So, $x+2(180-x)=2 \times 100$
$x+360-2x=200$
$x=160$
% of $Cu^{+}$ ions $= \cfrac {160}{180} \times 100=88.9$%

Multiple choice imperfections in solids solid state the solid state chemistry

If $NaCl$ is doped with ${ 10 }^{ -4 }mol$% of ${ SrCl } _{ 2 }$, the concentration of cation vacancies will be: $\left( { N } _{ A }=6.02\times { 10 }^{ 23 }{ mol }^{ -1 } \right) $:

  1. $6.02\times { 10 }^{ 15 }{ mol }^{ -1 }$
  2. $6.02\times { 10 }^{ 16 }{ mol }^{ -1 }$
  3. $6.02\times { 10 }^{ 17 }{ mol }^{ -1 }$
  4. $6.02\times { 10 }^{ 14 }{ mol }^{ -1 }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$NaCl$ is doped with $10^{-4}$ $mol\%$ of $SrCl _2$, i.e., one mole of $NaCl$ will have $10^{-6}$ mol of $SrCl _2$

$\rightarrow Sr^{+2}$ will replace one cation.
Therefore, concentration of cation vacancy $=10^{-6}\times 6.022\times 10^{23}=6.022\times 10^{17}$ $mol^{-1}$

Multiple choice imperfections in solids solid state the solid state chemistry

The mineral hawleyite, one form of $CdS$, crystallizes in one of the cubic lattices , with edge length 5.87 A The density of hawleyite is $ 4.63 g cm^{-3} $
In which cubic lattice does hawleyite crystallizes?

  1. end centred cubic

  2. body centered cubic

  3. face centred cubic

  4. edge centred cubic
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Density of Howlegite $=4.63g/{ cm }^{ 3 }$  $(P)$

Edge length $={ 5.87A }^{ 0 }=5.87\times { 10 }^{ -8 }cm$ $(a)$
Density $\left( P \right) =\dfrac { z\times { a }^{ 3 }\times { N } _{ 0 } }{ M } $                                 $M=$ Molar mass of $cds=144g/mol$
$z=\dfrac { 4.63\times { \left( 5.87\times { 10 }^{ -8 } \right)  }^{ 3 }\times 6.02\times { 10 }^{ 23 } }{ 144 } $        $N=$ Avagadro Number $=6.023\times { 10 }^{ 23 }$
$=3.9\cong 4\quad \quad z=4$
$\therefore$   There are four formula units of cds present in on unit cell.
$\Rightarrow $  Face entered cubic lattice.

Multiple choice imperfections in solids solid state the solid state chemistry

Which is correct statement?

  1. Schottky defect occurs when radius of cation is smaller

  2. When temperature increases then number of defects decreases

  3. Frenkel defect occurs when radius of cation is smaller

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As temperature and number of defects are inversely propotional, with increase in temperature number of defects decreases. 

In schottky effect, size of ions are almost same while in frenkel defect, size of cation is small .