Tag: imperfections in solids

Questions Related to imperfections in solids

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 $\text{A}$

An ionic solid has some point defect but its experimental density is equal to its theoretical density. The type of defect is:

imperfections in solids solid state the solid state chemistry

  1. Schottky defect

  2. Frenkel effect

  3. Metal excess defect

  4. Metal deficient defect

Show answer
Correct Option: B
Explanation:
An ionic solid has some point defect but its experimental density is equal to its theoretical density. The type of defect is Frenkel effect.

When an ion leaves its correct lattice site and occupies an interstitial site, Frenkel defect is observed. Hence, the density of crystal is not affected.

In Schottky defect, the density of the crystal decreases.

Ionic solids with Schottky defects contain in their structure

imperfections in solids solid state the solid state chemistry

  1. equal number of cations and anions vacancies

  2. interstitial anions and anion vacancies

  3. cation vacancies only

  4. cation vacancies and interstitial cations

Show answer
Correct Option: A
Explanation:

Schottky defect is the defect which is produced when one cation and anion is 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.

In a solid lattice, the cation has left a lattice site and is located at an interstitial position. The lattice defect is known as____________.

imperfections in solids solid state the solid state chemistry

  1. Interstitial defect

  2. Valency defect

  3. Frenkel defect

  4. Schottky defect

Show answer
Correct Option: C
Explanation:

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.
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.

Schottky defect defines imperfection in the lattice structure of :

imperfections in solids solid state the solid state chemistry

  1. solid

  2. gas

  3. liquid

  4. plasma

Show answer
Correct Option: A
Explanation:

A Schottky defect is a type of point defect in a solid crystal lattice. 

Schottky defect is noticed in:

imperfections in solids solid state the solid state chemistry

  1. $NaCl$

  2. $KCl$

  3. $BeCl _2$

  4. both $A$ and $B$

Show answer
Correct Option: D
Explanation:

All alkali metal halides show the Schottky defect due to the formation of excess cations.
Thus Schottky defect will be noticed in $NaCl \; & \; KCl$.
Thus, option $(D)$ is right answer.