Tag: the solid state

Questions Related to the solid state

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

imperfections in solids solid state the solid state chemistry

  1. True

  2. False

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Correct Option: B
Explanation:

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

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 :

imperfections in solids solid state the solid state chemistry

  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. $\left (\dfrac {N _1}{N}\right )^{\dfrac{1}{2}} exp^{(E _i/2KT)}$

Show answer
Correct Option: A
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 $\left (\dfrac{N}{N _1} \right )^{\dfrac{1}{2}} exp^{(-E _i/2KT)}$

Statement: Solids with Schottky defects are electrical insulators.

State whether the given statement is true or false.
imperfections in solids solid state the solid state chemistry

  1. True

  2. False

Show answer
Correct Option: B
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 $\text{false}$

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

imperfections in solids solid state the solid state chemistry

  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.

Show answer
Correct Option: B,C
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).

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.
imperfections in solids solid state the solid state chemistry

  1. True

  2. False

Show answer
Correct Option: A
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.

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.

imperfections in solids solid state the solid state chemistry

  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

Show answer
Correct Option: A
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.

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.

imperfections in solids solid state the solid state chemistry

  1. TFFF

  2. FTTF

  3. TFFT

  4. TFTF

Show answer
Correct Option: D
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 $\text{D}$

Frenkel defect is generally observed in___________.

imperfections in solids solid state the solid state chemistry

  1. AgBr

  2. AgI

  3. ZnS

  4. all of the above

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Correct Option: D
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.

Select the correct statement regarding F-centre.

imperfections in solids solid state the solid state chemistry

  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.

Show answer
Correct Option: D
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.

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

imperfections in solids solid state the solid state chemistry

  1. low

  2. $1.3$

  3. $1.5$

  4. slightly less than unity

Show answer
Correct Option: A
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 $\text{A}$