Tag: chemistry

Quizzes (490) Questions (9892)

Questions Related to chemistry

Multiple choice imperfections in solids solid state the solid state chemistry

Formula of metal oxide with metal deficiency defect in its crystal is $A _{0.8}O$. The crystal contains $A^{2+}$ and $A^{3+}$ ions. The fraction of metal existing as $A^{2+}$ ions in the crystal is

  1. $0.96$
  2. $0.04$
  3. $0.50$
  4. $0.31$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Solution:- (C) $0.50$

Fiormula is ${A} _{0.8}O$
So the ratio of $A : O = 80 : 100$
Thus, if there are $100$ atoms of oxygen then $80$ atoms of $A$.
Let $x$ be the no. of atopms of ${A}^{+2}$.
No. of atoms of ${A}^{+3} = 80 - x$
Charge on $A \; =$ Charge on $O$
Since oxygen has charge $-2$.
Therefore,
$2x + 3 \left( 80 - x \right) = 2 \times 100$
$2x + 240 - 3x = 200$
$\Rightarrow x = 40$
Therefore,
Fraction of ${A}^{+2} = \cfrac{\text{atoms of } {A}^{+2}}{\text{Total no. of atoms}}$
$\Rightarrow$ Fraction of ${A}^{+2} = \cfrac{40}{80} = 0.50$

Multiple choice imperfections in solids solid state the solid state chemistry

The non-stoichiometric compound, titanium monoxide has a continuous range of composition from $Ti _{0.75}O$ to $TiO _{0.69}$ Which of the following is/are the correct regarding the possible composition of the compound ? $[Ti=48]$

  1. The maximum percentage by mass of oxygen in the compound is $30.8$
  2. The minimum percentage by mass of titanium in the compound is $69.2$
  3. The minimum percentage by mass of oxygen in the compound is $18.7$
  4. The minimum percentage by mass of titanium in the compound is $82.3$
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Multiple choice imperfections in solids solid state the solid state chemistry

Which of the following defect, if present, lowers the density of the crystal?

  1. Frenkel

  2. Schottky

  3. Metal excess defect due to excess cation

  4. interstitial defect
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Schottky defects involve the removal of ions from the lattice, which decreases the total mass of the crystal for the same volume, thus lowering the density.

Multiple choice imperfections in solids solid state the solid state chemistry

The only incorrect effect on density by the given defect in solids is

  1. Density must decrease by vacancy defect

  2. Density must increase by the interstitial defect

  3. Density must increase by impurity defect

  4. Density does not change by dislocation defect
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Vacancy defects decrease density because atoms leave the lattice. Interstitial defects increase density by adding atoms to voids. Impurity defects can either increase or decrease density depending on the size and mass of the impurity, but the statement that it must increase is not a universal rule, making it the most incorrect general claim.

Multiple choice imperfections in solids solid state the solid state chemistry

The intrinsic or thermodynamic defect is

  1. Schottky defect

  2. Metal excess defect due to excess cation

  3. Metal excess defect due to anion vacancy

  4. Metal-deficient defect
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Schottky defects are intrinsic or thermodynamic defects because they arise naturally in ionic crystals due to thermal vibrations, leading to the formation of vacancy pairs to maintain electrical neutrality.

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 and cations occupy all the tetrahedral voids
II. If the radius of cation and anion is $20$ and $95$ pm, then the coordination number of the cation is the crystal is $4$.
III. An atom or ion is transferred from a lattice site to an interstitial position in Frenkel defect.
IV. The density of crystal always increases due to substitutional impurity defect.

  1. TTTT

  2. FFFF

  3. FFTT

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

I is False: In anti-fluorite, anions form FCC and cations occupy all tetrahedral voids. II is True: Radius ratio 20/95 = 0.21, which falls in the range for coordination number 4. III is True: This is the definition of Frenkel defect. IV is False: Density can decrease if the impurity atom is smaller or lighter.

Multiple choice imperfections in solids solid state the solid state chemistry

Which kind of defect is introduced by doping in silicon crystal?

  1. Dislocation defect

  2. Schottky defect

  3. Frenkel defect

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

Doping silicon with elements like phosphorus or boron introduces extra electrons or holes, which are classified as electronic defects, altering the electrical conductivity of the semiconductor.