Chemistry Multiple Choice Questions on “Imperfections in Solids”.
1. What kind of order is present in a solid for it to be a perfectly crystalline solid?
a) Long range order
b) Short range order
c) No order
d) Both, short range and long range order
Answer: d
Clarification: Only short range order is a feature of amorphous solids. Crystalline solids exhibit both short and long range order. Crystalline solids are formed by repetitive arrangement of unit cells.
2. State whether true or false: The number of defects in a crystal can be minimized by carrying out the process of crystallization at a slow rate.
a) True
b) False
Answer: a
Clarification: All big crystals have some or the other defects in the arrangement of their constituents. An ideal crystal does not exist. These defects are more if the crystallization process occurs at a faster rate. Hence, slowing down the process minimizes the defects. It is akin to starting with one crystal (unit) and adding to it from all sides to create a bigger crystal. Defects are produced due to some irregularity in this arrangement.
3. In a crystal, if a fault exists in the arrangement at a point, it is called as _________
a) space defect
b) single defect
c) point defect
d) primary defect
Answer: c
Clarification: When there is a fault in the arrangement of a constituent particle such as an atom, ion or molecule, and the fault exists at a point in the lattice structure, it is called as a point defect.
4. In which type of point defect are the cations and anions absent in stoichiometric proportions?
a) Schottky defect
b) Frenkel defect
c) Impurity defect
d) The given situation does not occur for any point defect.
Answer: a
Clarification: A vacancy defect is when an atom, ion or molecule is absent from its position in the lattice. When this occurs for ionic solids, it is called a Schottky defect. Cations and anions are found to be absent in stoichiometric proportion so that the electrical neutrality of the crystal is maintained.
5. Schottky defects are observed in solids with cations and anions of similar sizes. Which of the following compounds, therefore, is NOT likely to have a Schottky defect?
a) NaCl
b) AgCl
c) CsCl
d) KCl
Answer: b
Clarification: There is a considerable size difference between Ag cation and Cl anion. Hence a Frenkel defect is more likely to occur than a Schottky defect.
6. Impurity defect is a type of point defect. It can occur __________
a) in one way, as substitution impurity defect
b) in one way, as interstitial impurity defect
c) in two ways, as substitution impurity defect or as interstitial impurity defect
d) in two ways, as vacant impurity defect or as interstitial impurity defect
Answer: c
Clarification: An impurity defect occurs when a regular ion is replaced by some other type of ion, e.g. Na+ is replaced by K+. If the replacement occurs in the place of the regular cation, it is called a substitution impurity defect. If the replacement occurs in an interstitial position, it is called an interstitial impurity defect.
7. Stainless steel is a/an ________ alloy.
a) vacant
b) interstitial
c) substitution
d) pure
Answer: b
Clarification: Stainless steel is an interstitial alloy. Carbon atoms are introduced into interstitial spaces of iron lattice as an impurity. Further alloying sees the introduction of nickel, chromium in the interstitial spaces.
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