Chemistry Test - 25

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.

Quartz glass does not have a perfectly ordered structure, hence it is classified as an amorphous solid. The rest are crystalline solids due to ordered structures.

Simple cubic lattice results from 3D close packing from 2D square-packed layers. When one 2D layer is placed on top of the other, the corresponding spheres of the second layer are exactly on top of the first one. Since both have the same, exact arrangement it is AAA type.

In face-centered cubic unit cell, atoms are present at each of the corners and at the centre of the face of the cube.

Thus, the total number of atoms in face-centered cubic unit cell: 1+3=4 atoms.

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.

Non-Ideal solutions do not obey Raoult’s law. For Non-Ideal solutions, ΔV_mixing ≠ 0, ΔH_mixing ≠ 0. Non-ideal solutions form azeotropes or constant boiling mixtures, i.e., they have the same concentration in the vapour phase and the liquid phase.

For a crystal lattice, if there are N close-packed spheres the number of tetrahedral voids are 2N and number octahedral voids are N. For N=6, number of tetrahedral voids = 2 × 6 = 12.

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.

Chlorobenzene + Bromobenzene is an example of an ideal solution. Chloroform + Benzene and Acetone + Aniline are examples of non-ideal solutions but they show negative deviations. Acetone + Carbon disulphide is an example of a non-ideal solution showing positive deviation.

Crystalline solids possess anisotropic nature within their structure. Anisotropy is the directional dependence of a property. Meaning, a property within the crystal structure will have different values when measured in different directions. Snowflake is a crystalline solid whereas the rest are amorphous solids.