Important Definitions of Chemistry Class 12

 

Important Definitions (PART-2)

This article has all the important definition terms of NCERT Chemistry Class 12 (Unit 6 to 14) which are commonly asked in Boards as well as various competitive examination. It certainly help you to score full marks.

Unit 6: General Principles and Processes of Isolation of Elements (Excluded in AISSCE 2021)

Minerals: The naturally occurring chemical substances in which metals occur in the earth’s crust are called minerals.

Ores: The mineral. From which the metal can be economically and conveniently extracted is called as ore.

Metallurgy: The process of extracting metals from their ores is called metallurgy.

Concentration of ore: the process of removing unwanted impurities (gangue) from the ore is called ore concentration or ore dressing or ore benefaction.

Calcination: The process of heating the ore strongly either in a limited supply of air or in the absence of air is known as calcination.

Froth floatation method: This is method of concentration of ore which is based on the principle of difference in the wetting properties of the ore and gangue particles with water and oil. It is used for the extraction of those metals in which the ore particles are preferentially wetted by oil and gangue by water.

Roasting: The process of heating the ore strongly  presence of excess of air at temperature below the melting point of the metal is known as roasting.

Hydrometallurgy: The process of extraction of metals by dissolving the ore in a suitable chemical reagent and the precipitation or displacement of the metal by more reactive or electropositive metal is called hydrometallurgy.

Refining: the process of purifying the crude metal is called refining.

Electrolytic refining: In this refining, the impure metal is made to act as anode and a strip of same metal in pure form is used as cathode and both are placed in suitable electrolytic solution of salt of same metal. On passing electric current, the metal ions from the electrolyte are deposited at the cathode in the pure form while the equivalent amount of metal dissolves from the anode into electrolyte. The impurities fall down as anode mud.

For eg: The electrolytic refining  of Cu.

At Cathode:  Cu²⁺ + 2 e^- ----à Cu

At Anode:  Cu --àCu²⁺ + 2 e^-

Zone refining: The principle of this method is that the impurities are more soluble in the melt than in the solid state of the metal. A circular mobile heater is fixed at the end the impure metal bar. As the heater moves slowly, the impurities also move into the adjacent molten part. In this way impurities are made to move into one end which is finally cut off and discarded.

This method is very useful forproducing semiconductor and other metals ofvery high purity, e.g., germanium, silicon,boron, gallium and indium.

Vapour phase refining: In this method the following requirements are needed

a)  The metal should form a volatile compound with an available reagent.

b)  The volatile compound should be easily decomposable so that metal can be easily recovered.

Mond process: In this process Ni is heated in a stream of CO to form a volatile nickel carbonyl Ni(CO)₄.

The carbonyl vapours when subjected to higher temperature (450-700K) undergoes thermal decomposition giving pure nickel.

Van Arkel Method: In this method Ti or Zr are heated with Iodine to form metal iodide.

The metal iodide is decomposed on a tungsten filament, electricallyheated to about 1800K. The pure metal deposits on the filament.

For more detailed notes click here.

 

Unit 8: d- & f- block elements

Lanthanoid contraction: The steady decrease in atomic and ionic sizes of lanthanoid elements with increasing atomic number is called lanthanoid contraction.

Mischmetal: The alloy which consist of a lanthanoid metal (about 95%). Iron (about 5%) and traces of S, C, Ca, Al etc is known as mischmetal.

 For more detailed notes click here.

Unit 9: Coordination compounds

Coordination entity: A coordination entity constitutes a central atom or ion bonded to fixed number of oppositely charged ions or neutral molecules.

Central atom: The atom or ion to which a fixed number of neutral molecules or ions are attached in the coordination entity is called central atom or ion.

Ligands: The ligand is an atom or molecule or ion which is capable of donating a pair of electrons to the central metal or ion and forms a coordinate bond with it.

Denticity: The number of coordinating or ligating groups present in a ligand is called the denticity of the ligand.

Chelation: When a di- or a polydentate ligand uses its two or more donor atoms to bind to the same central metal atom or ion, it is called chelation. The complex formed is known as chelate and the ligand is known as cheating ligand.

Ambidentate ligand: The monodentate ligand which can coordinate with the central atom through more than one site are called ambidentate ligand.

Coordination number: The total number of ligands attached to a central atom or ion is called the coordination number of that ion.

Coordination polyhedral: The spatial arrangement of ligand atoms which are directly attached to the central atom is known as coordination polyhedral.

Homoleptic and Heteroleptic complexes: the complexes in which the metal is bound to only one kind of donor groups are called homoleptic complexes and the complexes in which the metal is bound to more than one kind of donor groups are called heteroleptic complexes.

Crystal field splitting: The conversion of five degenerate d-orbitals of the metal ion into different sets of orbitals having different energies in the presence of electrical field of ligands is called crystal field splitting.

Crystal field splitting energy: The energy difference between the two ets of energy levels is called crystal field splitting energy.

For more detailed notes click here.

 

Unit 10: Haloalkanes & Haloarenes

All Name reactions: Click here

SN1 and SN2 Reactions: Click here

Chirality: The molecules which are not superimposable on their mirror images are called chiral molecules. And the property of non-superimposability of structure on its mirror image is called chirality.

Enantiomers: The Non-superimposable mirror images are known as enantiomers.

Racemisation: The equimolar mixture of the enantiomers (dextro and laevo froms) is called racemic mixture. And the phenomenon of converting d- or l- form of compound into racemic form (dl) is called racemization.

For more detailed notes click here.

Unit 11: Alcohols, Phenols & Ethers

All Name reactions: Click here

Reaction mechanisms

(i)                Ethene to ethanol. Click here

(ii)              Ethanol to ethane. Click here

(iii)           Ethanol to ethoxy ethane. Click here

(iv)             Esterification. Click here

(v)               Reaction of Ethanol with excess HI. Click here

For more detailed notes click here.

Unit 12: Aldehydes, Ketones & Carboxylic acid

All Name reactions: Click here

For more detailed notes click here.

Unit 13: Amines

All Name reactions: Click here

Zwitter Ion: The dipolar ion which has both charges (positive and negative) due to presence of both acidic and basic groups is known as zwitter ion. For eg. Sulphanilic acid & Amino acids.

For more detailed notes click here.

Unit 14: Biomolecules

Carbohydrates: The optically active polyhydroxy aldehydes oy polyhydroxy ketones or the compounds which produce such compounds on hydrolysis are called carbohydrates.

Anomers: The pairs of optical isomers which differ in the configuration only around C₁ atom are called anomers. For eg. α-D-glucose and β-D-glucose.

Glycosidic Linkage: The linkage between two monosaccharide units through oxygen atom is called glycosidic linkage.

Invert sugar: There is change in the sign of rotation from dextro before hydrolysis to laevo after hydrolysis of sucrose, the reaction is called inversion reaction and the mixture (glucose and fructose) is called invert sugar.

Proteins: The proteins are condensation polymers of α-amino acids. They are also called as polypeptides.

Amino acids: The compounds which contain both amino and carboxyl group are called amino acids.

Essential & non-essential amino acids: The amino acids which can not be made or synthesize by our body, and we require them in our diet are called essential amino acids. The amino acids which can be made or synthesize by our body, and we do not require them in our diet are called non-essential amino acids.

Peptide linkage: The linkage between two amino acids through –CO-NH- bond is called peptide linkage.

Denaturation of Proteins: The process which changes the physical and biological properties of proteins without affecting the chemical composition of a protein is called denaturation of protein.

Vitamins: These are the organic compounds which cannot be produced by the body and must be supplied in small amounts in diet to perform specific biological functions for the normal health, growth and maintenance of body.

Nucleic acids: These are biologically important polymers of nucleotides which are present in all living cells.

Phospho-diester linkage: The linkage between two nucleotide units is called Phospho-diester linkage.

For more detailed notes click here.

Unit 15: Polymers (Excluded in AISSCE 2021)

Unit 16: Chemistry in everyday Life (Excluded in AISSCE 2021)

 

By: Satyam Kumar Nigam

PGT Chemistry