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Multiple choice imperfections in solids solid state the solid state chemistry

Non-stoichiometric compounds is/are :

  1. $Cu _2O$
  2. $Cu _2S$

  3. FeO
  4. $Hg _2Ba _2YCaCu _2O _ 7$
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
Explanation
Non-stoichiometric compounds are chemical compounds with an elemental composition that cannot be represented by usual integral numbers. They are almost always inorganic compounds and almost invariably solids. In such materials, some small percentage of atoms are missing or too many atoms are packed into an otherwise perfect lattice work. They exhibit special electrical or chemical properties because of these flaws or defects. For example, when atoms are missing, the other atoms can move through the solid more rapidly. Non-stoichiometry is represented by many metal oxides and sulfides. For example, stoichiometric iron(II) oxide, which is rare, has the formula FeO whereas the more common nonstoichiometric material has the formula $Fe _{0.95}O$. Non-stoichiometric compounds are homogeneous, they are not mixtures. Batteries often rely on materials that can exist in a range of non-stoichiometric states.
Therefore, all given compounds are non-stoichiometric.
Multiple choice imperfections in solids solid state the solid state chemistry

Assertion: Frenkel defects are shown by $AgX$.
Reason: $Ag^+$ ions have small size.

  1. Both Assertion and Reason are correct and Reason is the correct explanation of Assertion

  2. Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

  3. Assertion is correct but Reason is not correct

  4. Assertion is not correct but Reason is correct

  5. Both Assertion and Reason are not correct
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Frenkel defect is the 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.
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. Examples are $ZnS, AgBr, AgI, AgCl$.

Multiple choice imperfections in solids solid state the solid state chemistry

The compounds having the general molecular formula $A^{2+ }Fe _{2.047}$are called Ferrites.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$General\; formula\; of\; Ferrites\; is\; { m }^{ 2+({ Fe } _{ 2 }{ O } _{ 4 }) }\ \; \; \; eg.\; \; ZnF{ e } _{ 2 }{ O } _{ 4 }\ Hence\; the\; above\; statement\; is\; false.$

Multiple choice imperfections in solids solid state the solid state chemistry

There are N atoms in a crystal with $N _1$ interstitial positions in its structure. If there are n Frenkel defects in the crystal, then n is equal to :

  1. $\left (\dfrac{N}{N _1} \right )^{\dfrac{1}{2}} exp^{(-E _i/2KT)}$
  2. $\left (\dfrac{N _1}{N}\right )^{\dfrac{1}{2}} exp^{(-E _i/2KT)}$
  3. $\left (\dfrac{N}{N _1}\right )^{\dfrac{1}{2}} exp^{(E _i/2KT)}$
  4. $\left (\dfrac {N _1}{N}\right )^{\dfrac{1}{2}} exp^{(E _i/2KT)}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

There are N atoms in a crystal with $N _1$ interstitial positions in its structure. If there are n Frenkel defects in the crystal, then n is equal to $\left (\dfrac{N}{N _1} \right )^{\dfrac{1}{2}} exp^{(-E _i/2KT)}$

Multiple choice imperfections in solids solid state the solid state chemistry
Statement: Solids with Schottky defects are electrical insulators.

State whether the given statement is true or false.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Solids with Schottky defects conducts electricity to a small extent by the ionic mechanism. The defect is due to an unequal number of cation and anion vacancies because in it some cations leave vacant spaces


Hence, the given statement is $\text{false}$

Multiple choice imperfections in solids solid state the solid state chemistry

Which of the following statements regarding defects in solids is/are correct?

  1. Frenkel defect is usually favoured by a very small difference in the sizes of cation and anion.

  2. Frenkel defect is a dislocation defect.

  3. Trapping of an electron in the lattice leads to the formation of F-center.

  4. Schottky defects have no effect on the physical properties of solids.
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation

Frenkel defect is a defect 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.
Consequences of Frenkel defect:
1. The closeness of like charges tends to increase the dielectric constant of the crystal.
2. The crystal showing a Frenkel defect conducts electricity to a small extent by ionic mechanism.
3. The density of the crystal remains the same.
In metal excess defects caused by anion vacancies, one or more anions are missing from the lattice points which are occupied by electrons.
The overall electrical neutrality is maintained. When NaCl crystal is heated with Na vapours, this kind of defect is observed.
The electrons impart colour to the crystal (yellow colour to NaCl). These are known as F-centers (Farbe's centres).

Multiple choice imperfections in solids solid state the solid state chemistry
Statement: The addition of $\text{CaCl} _2$ to $\text{KCl}$ crystal lowers the density of the $\text{KCl}$ crystal. 

State whether the given statement is true or false.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Doping with $Ca^{2+}$ ions will create two vacant sites occupied by $K^+$ ions. One site will be occupied by $Ca^{2+}$ ions leaving one site. So, the density is lowered.

Multiple choice imperfections in solids solid state the solid state chemistry

Assertion: In any ionic solid (MX) with Schottky defect, the number of positive and negative ions are same.
Reason: An equal number of cation and anion vacancies is present.

  1. Assertion and Reason are correct and Reason is the correct explanation of Assertion

  2. Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

  3. Assertion is correct but Reason is not correct

  4. Assertion is not correct but Reason is correct
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Schottky defect is a defect which is produced when one cation and anion are 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

Give the correct order of initials T (true) or F (False) for following statements:
I. In an anti-fluorite structure, anions form FCC lattice and cations occupy all tetrahedral voids.
II. If the radius of cations and anions are $0.2\ \mathring A$ and $0.95\ \mathring A$, then co-ordination number of cation in the crystal is $4$.
III. An ion is transferred from a lattice site to an interstitial position in Frenkel defect.
IV. Density of crystal always increases due to substitutional impurity defect.

  1. TFFF

  2. FTTF

  3. TFFT

  4. TFTF
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

I. In an anti-flourite structure, anions form FCC lattice and cations occupy all tetrahedral voids.


II. Ratio of radius $= \dfrac{0.2}{0.95} = 0.21$ which lies between $0.155-0.225$ and so, it has co-ordination number of $3$.


III. 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.

IV. The density of crystal may increase/decrease due to substitutional impurity defect.


Hence, the correct option is $\text{D}$

Multiple choice imperfections in solids solid state the solid state chemistry

Frenkel defect is generally observed in___________.

  1. AgBr

  2. AgI

  3. ZnS

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

Schottky defect is observed in the crystals of NaCl, CsCl, AgBr etc.

Frenkel defect is observed in the crystals of ZnS, AgBr, AgI, AgCl etc.