16 Questions
Why does the conductivity of a solution decrease on dilution?
The number of ions per cm3 decreases on dilution.
Why is AC current used instead of DC in measuring electrolytic conductance?
AC Current is used to prevent Electrolysis of the solution.
What is a Positive Catalyst? Provide an example.
A positive catalyst increases the rate of reaction. For example, Fe acts as a positive catalyst in the Haber process for manufacturing NH3.
What is a Negative Catalyst? Provide an example.
A negative catalyst decreases the rate of reaction. For example, glycerol acts as a negative catalyst in the decomposition of H2O2.
Define coordination number of a crystal.
The number of nearest neighbours that is surrounding an ion in a crystal is called as coordination number.
What is the coordination number of atoms in BCC?
For BCC it is 8.
Define molecular crystals.
The neutral molecule occupies in the lattice point of crystal. They have van der Waals forces.
What are the different types of Primitive Unit cells?
Cubic, Tetragonal, Orthorhombic, Hexagonal, Monoclinic, Triclinic, Rhombohedral.
Draw the structure of a Simple Cubic (SC) crystal and state the total number of atoms in SC.
In SC, there is 1 atom in total.
Explain the types of molecular crystals.
Non-polar molecular crystals have weak London forces (e.g., Naphthalene). Polar molecular crystals have Dipole-Dipole interactions (e.g., Solid CO2). Hydrogen bonded molecular crystals have Hydrogen bonds (e.g., Ice).
What is the definition of packing efficiency?
Packing efficiency = Total volume occupied by the spheres / Volume of the unit cell * 100
Define crystal lattice.
The regular arrangement of the ions in a crystal is called as crystal lattice.
Differentiate between crystalline and amorphous solids.
Crystalline solids have an orderly arrangement of atoms, definite shape, anisotropic properties, true solids, and a definite heat of fusion. Amorphous solids have a random arrangement of atoms, irregular shape, isotropic properties, act as super cooled liquids, and do not have a definite heat of fusion.
Explain the Frenkel defect.
Frenkel defect arises from the dislocation of ions within the crystal lattice. It does not affect the density of the crystal. E.g., AgBr
Explain the Schottky defect.
Schottky defect occurs due to the equal number of anion and cation vacancies in the crystal lattice. It reduces the density of the crystal. E.g., NaCl
What is the meaning of isotropy?
Isotropy refers to when the physical properties are identical in all directions.
Study Notes
Conductivity of Solutions
- Conductivity of a solution decreases on dilution because the number of ions per unit volume decreases, leading to a decrease in the number of charge carriers.
Measuring Electrolytic Conductance
- AC current is used instead of DC in measuring electrolytic conductance because DC can cause electrolysis, which alters the composition of the solution being measured, whereas AC does not.
Catalysts
- A Positive Catalyst is a substance that increases the rate of a chemical reaction without being consumed by the reaction. Example: Vanadium pentoxide (V2O5) in the production of sulfuric acid.
- A Negative Catalyst is a substance that decreases the rate of a chemical reaction without being consumed by the reaction. Example: Iodine in the reaction between hydrogen peroxide and potassium iodide.
Crystal Structures
- The coordination number of a crystal is the number of nearest neighbor atoms surrounding a central atom.
Body-Centered Cubic (BCC) Crystals
- In BCC crystals, each atom is surrounded by eight nearest neighbors, so the coordination number is 8.
Molecular Crystals
- Molecular crystals are solids composed of individual molecules, which are held together by intermolecular forces such as van der Waals forces, hydrogen bonds, or dipole-dipole interactions.
Primitive Unit Cells
- Primitive unit cells are the smallest three-dimensional units of a crystal lattice that can be repeated in three-dimensional space to form the entire crystal.
- The different types of primitive unit cells are Simple Cubic (SC), Body-Centered Cubic (BCC), Face-Centered Cubic (FCC), and Hexagonal Close-Packed (HCP).
Simple Cubic (SC) Crystal Structure
- A Simple Cubic (SC) crystal structure consists of atoms located at the corners of a cube, with each atom being shared by eight adjacent cubes.
- A Simple Cubic crystal has a total of 1 atom per unit cell.
Molecular Crystals
- Molecular crystals can be classified into four types: Molecular Solids, Hydrogen-Bonded Molecular Solids, Polar Molecular Solids, and Non-Polar Molecular Solids.
Packing Efficiency
- Packing efficiency is the percentage of the total volume of a unit cell occupied by the atoms or molecules that make up the crystal.
Crystal Lattice
- A crystal lattice is a three-dimensional arrangement of points in space, where each point represents an atom or group of atoms.
Crystalline and Amorphous Solids
- Crystalline solids have a regular, periodic arrangement of atoms, whereas amorphous solids have a random, non-periodic arrangement of atoms.
Frenkel Defect
- A Frenkel defect is a type of point defect in which an ion is missing from its lattice site and occupies an interstitial position.
Schottky Defect
- A Schottky defect is a type of point defect in which an equal number of cations and anions are missing from their lattice sites, resulting in no net charge.
Isotropy
- Isotropy is the property of a material having the same properties in all directions, i.e., it looks the same in every direction.
Learn about the concept of solvate and hydrate isomerism in coordination compounds by comparing [Co(H2O)5Cl] Br and [Co(H2O)5 Br] Cl. Also, explore solid state unit cell concepts and characteristics of ionic crystals such as conductivity and hardness.
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