Tag: imperfections in solids

Questions Related to imperfections in solids

Scotty defect is observed in____________.

imperfections in solids solid state the solid state chemistry

  1. $NaCl$

  2. $KCl$

  3. $CsCl$

  4. $BaCl _2$

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Correct Option: A,B,C
Explanation:

Schottky defect is the 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.
For Schottky defect, co-ordination numbers of the ions should be high., Examples of ionic solids showing this defect are NaCl, CsCl, KCI, KBr etc.
Consequences of Schottky defect are as follows:
1. Density of the crystal decreases.
2. The crystal begins to conduct electricity to small extent by ionic mechanism.
3. The presence of too many voids lowers lattice energy or the stability of the crystal.

Statement: The imperfectness in crystal increases with increase in temperature.

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

  1. True

  2. False

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Correct Option: A
Explanation:
The imperfectness in crystal increases with increase in temperature. Hence, these imperfections are called thermodynamic defects. When the temperature is high, imperfections are high and when the temperature is low, imperfections are low.
Statement: Imperfection in solids give rise to new properties in it.

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

  1. True

  2. False

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Correct Option: A
Explanation:
Imperfection in solids changes the properties of crystals and gives rise to new properties in it. These include electrical and thermal conductivity and density.

Non-stoichiometric compounds is/are :

imperfections in solids solid state the solid state chemistry

  1. $Cu _2O$

  2. $Cu _2S$

  3. FeO

  4. $Hg _2Ba _2YCaCu _2O _ 7$

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Correct Option: A,B,C,D
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.

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

imperfections in solids solid state the solid state chemistry

  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

Show answer
Correct Option: A
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 $ZnS, AgBr, AgI, AgCl$.

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.