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Laws & Definition HSC Chemistry

Table of Content (toc)

Chapter 1. Solid State
  (1) Unit cell. 
 Ans. It is the smallest repeating structural unit of a crystalline. solid (or crystal lattice) which when repeated in different directions produces the crystalline solid (lattice). 

 (2) Isomorphism.
 Ans. A phenomenon in which two or more crystalline substances show same crystalline structure is called isomorphism and the crystals are said to be isomorphous. For example, K.SO, and K,SCO,. 

 (3) Anisotropy.
 Ans. The ability of crystalline solids to change their physical. properties when measured different directions is called anisotropy. 

 (4) Polymorphism.
 Ans. A phenomenon in which when a single substance crystallises in two or more forms under different conditions of solidification is called polymorphism and the substance is called polymorphous.

(3) Packing efficiency.. 
 Ans. It is the percentage of total space in the unit cell occupied by the constituent particles like atoms, ions or molecules of the crystal. 

 (6) Isotropy. 
 Ans. The ability of amorphous solids to exhibit identical physical properties even though measured in different directions is called isotropy. 

 (7) Coordination number. 
 Ans. The number of the closest neighbouring constituent particles like atoms, ions or molecules which are in contact with a particular particle or an atom in the crystal lattice is called coordination number of that particle. In the crystal lattice all atoms may have same or different coordination numbers. 

(8) Schottky defect. 
 Ans. In case of ionic solids, the vacancies are produced due to absence of cations and anions and these defects are called Schottky defects. 

(9) Frenkel defect. 
 Ans. This defect arises when an ion of an ionic compound is missing from its regular site and occupies interstitial vacant position between the lattice points.
(10) Colligative property. 
 Ans. The property of a solution which depends on the total number of particles of the solute (molecules, lons) present in the solution and does not depend on the nature or chemical composition of solute particles is called colligative property of the solution.

 (11) Vapour pressure. 
 Ans. The pressure exerted by the vapour of a liquid (or solid) when it is in equilibrium with the liquid (or solid) phase at a constant temperature is called the vapour pressure of the liquid (or solid). Ans. It is defined as the elevation in boiling point, produced by 

 (12) Molal elevation constant. dissolving one mole of a solute in 1 kg (or 1000 g) of a solvent (Le. 1 molal solution). 1 

 (13) Osmosis. 
 Ans. It is defined as a pontaneous unidirectional flow of thei solvent molecules from a pure solvent or a dilute solution to the more concentrated solution through a semipermeable membrane.

 (14) Osmotic pressure.
 Ans. The osmotic pressure is defined as the excess mechanical pressure required to be applied to a solution separated by a semipermeable membrane from pure solvent or a dilute solution to prevent the osmosis or free passage of the solvent molecules at a given temperature.

 (15) Isotonic solutions. 
 Ans. The solutions having the same osmotic pressure at a given temperature are called isotonic solutions.

 (16) Freezing point. 
 Ans. The freezing point of a liquid is defined as the temperature at which the solid coexists in the equilibrium with the liquid and the vapour pressures of the liquid and the solid are equal. 

 (17) Boiling point. 
 Ans. The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid becomes equal to the external pressure, i.e. the atmospheric pressure (1 atm), e.g. the boiling point of water at 1 atm is 373 K.
(18) Lewis acid. 
Ans. According to Lewis theory, an acid is a substance which can accept a pair of electrons. For example, BF,. 

 (19) pH. 
 Ans. The negative logarithm, to the base 10, of the molar concentration of hydrogen ions, H is known as the pH of a solution. pH logolH*]

 (20) Ionic product of water. 
 Ans. It is defined as the product of molar concentrations of hydronium ions (or hydrogen ions) and hydroxyl ions at equilibrium in pure water at constant temperature. It is represented as, K[H₂O'] x [OH ] At 25°C, K=1x 10-¹4. 

 (21) Hydrolysis. 
 Ans. A reaction in which the cations or anions or both the ions of a salt react with water to produce acidity or basicity or sometimes neutrality is called hydrolysis. 

 (22) Buffer solution. 
 Ans. It is defined as a solution which resists the change in pH even after the addition of a small amount of a strong acid or a strong base or on dilution or on addition of water. 

 (23) Solubility product. 
 Ans. The product of equilibrium concentrations of the constituent ions raised to the power equal to their respective coefficients in the balanced equilibrium expression for the saturated solution of sparingly soluble electrolyte (like salt) at a given temperature is called solubility product. 

 (24) Common ion effect.
 Ans. The suppression of the degree of dissociation of a weak electrolyte by the addition of a strong electrolyte having an ion in common with the weak electrolyte is called common ion effect. For example, CH,COOH and CH,COONa have common ion CH,COO™

. (25) POH. 
 Ans. The negative logarithm, to the base 10, of the molar concentration of hydroxyl ions, OH is known as the pOH of a solution. pOH = -log[OH-].
(26) Closed system.. 
 Ans. It is defined as a system which can exchange only energy but not the matter with its surroundings, e.g. a closed vessel containing hot water so that only heat is lost to the surroundings and not the matter.

 (27) Extensive property.
 Ans. It is defined as a property of a system whose magnitude depends on the amount of matter present in the system, e.g. mass, volume

.. (28) Isothermal process.
 Ans. It is defined as a process in which the temperature of the system remains constant throughout the change of a state of the system. In this, AT=0.

 (29) Enthalpy (H). 
 Ans. It is defined as the total energy of a system consisting of internal energy (U) and pressure-volume (P x V) type of energy, i.e. enthalpy represents the sum of internal energy U and product PV energy. It is denoted by H and is represented as H U enthalpy internal energy + PV P-V energy

  (30) Enthalpy of fusion. 
Ans. The enthalpy change that accompanies the fusion of one mole of a solid into a liquid at constant temperature and pressure is called enthalpy of fusion. For example, H₂O(s) 1 atm, 273 K H₂O) AusH-6.01 kJ mol-¹ 

 (31) Thermodynamic standard state of a substance. 
Ans. The thermodynamic standard state of a substance. (compound) is the most stable physical state of it at 298 K and 1 atmosphere (or 1 bar). The enthalpy of the substance in the standard state is represented as AH".

 (32) Bond enthalpy (or Bond energy). 
Ans. The enthalpy change or amount of heat energy required to break one mole of particular covalent bonds of gaseous molecules forming free gaseous atoms or radicals at constant temperature (298 K) and pressure (1 atmosphere) is called bond enthalpy or bond energy. For example, bond enthalpy of H, is 436.4 kJ mol ¹.

 (33) Entropy. 
 Ans. Being a state function and thermodynamic function it is defined as entropy change (AS) of a system in a process which is equal to the amount of heat transferred in a reversible manner (Qrey) divided by the absolute temperature (T), at which the heat is absorbed. Thus, Entropy change= Heat transferred reversibly Absolute temperature of heat transfer AS= Qrev T
(34) Cell constant. 
 Ans. Cell constant of a conductivity cell is defined as the ratio of the distance between the electrodes divided by the area of cross section of the electrodes.

 (35) Specific conductance or conductivity. 
Ans. It is the conductance of a conductor that is 1 m in length and 1 m² in cross section area in SI units. (In C.G.S. units, it is the resistance of a conductor that is 1 cm in length and 1 cm² in cross section area.) It is the conductance of a conductor of volume 1 m³ (or in C.G.S. units, the volume of 1 cm³).

 (36) Molar conductivity. 
 Ans. It is defined as a conductance of a volume of the solution containing ions from one mole of an electrolyte when placed between two parallel plate electrodes 1 cm apart and of large area, sufficient to accommodate the whole solution between them, at constant tempera ture. It is denoted by Am

  (37) Faraday. 
 Ans. It is defined as the quantity of the electric charge on one mole of electrons. It has value, 1F-96500 C/mol. 

 (38) Electrode potential. 
 Ans. It is defined as the difference of electrical potential established due to electrode half reaction between metal electrode and the solution around it at equilibrium at constant temperature. 

 (39) Standard electrode potential. 
 Ans. It is defined as the difference of electrical potential between metal electrode and the solution around it at equilibrium when all the substances involved in the electrode reaction are in their standard states of unit activity or concentration at constant temperature.

 (40) Electrochemical series or electromotive series. 
Ans. It is defined as the arrangement in a series of electrodes of elements (metal or non-metal in contact with their ions) with the electrode half reactions in the decreasing order of their standard. reduction potentials.
(41) Rate law (or differential rate law).
 Ans. It is defined as an experimentally determined mathematical equation which expresses the rate of a chemical reaction in terms of molar concentrations of the reactants which influence the rate of the reaction. For example, for a reaction, A + B→ Products By rate law, Rate=R=k[A] x [B] where k is a rate constant and [A] and [B] are molar concentrations of the reactants A and B respectively. 

 (42) Rate constant. 
 Ans. The rate constant of a chemical reaction is defined as the rate of the chemical reaction when the concentration (or active masses) of each reactant has unit value, i.e. 1 mol dm in the case of solution and the pressure is 1 atm in case of gases, e.g. for a reaction, A→ products, Rate R=k[A]. If [A] = 1 mol dm, then k=R

. (43) Order of a chemical reaction.
 Ans. The order of a chemical reaction is defined as the number of molecules (or atoms) whose concentrations influence the rate of the chemical reaction. 
 The order of a chemical reaction is defined as the sum of the powers (or exponents) to which the concentration terms of the reactants are raised in the rate law expression for the given reaction.
(44) p-Block elements.
 Ans. The elements in which the differentiating electron (last filling electron) enters the p-orbital of the outermost shell of the atoms are called p-block elements. The elements of groups 16, 17 and 18 are p-block elements.

 (45) Interhalogen compounds.
 Ans. The compounds obtained from two different halogens are called interhalogen compounds. For example, CIF3, BrF3, ICI, etc.

 (46) Ozone umbrella. 
 Ans. The stratopheric pool of ozone which is a layer above earth's surface and protects from harmful high energetic ultraviolet (UV) rays is called ozone umbrella or ozonosphere.
(47) d-Block elements. 
 Ans. d-block elements are defined as the elements in which the differentiating electron enters d-orbital of the penultimate shell i.e. (n-1) d-orbital where 'n' is the last shell. The general electronic configuration can be represented as, (n-1)d¹-10, ns¹-2

 (48) Leaching. 
 Ans. It is a (chemical) process used in the concentration of an ore by extracting soluble material from an insoluble solid by dissolving in a suitable solvent. This method is used in the concentration process of ores of Al, Ag, Au, etc.

 (49) f-Block elements.
 Ans. Elements in which the differentiating electron enters into. the pre-penultimate shell, the (n-2) f-orbital are known as f-block elements. 0-1 1-14 The general electronic configuration is (n-2)(n-1)d ns².

 (50) Lanthanoids. 
 Ans. The series of fourteen elements from Ce to ,,Lu in which a differentiating electron enters 4f sub-shell and follows lanthanum is called lanthanoid series and the elements are called lanthanoids. 1-14 0-1 Their general electronic configuration is [Xe] 4f 5d

 (51) Actinoids. 
 Ans. The series of fourteen elements from ,,Th to 103Lr which follow actinium (9 Ac) and in which differentiating electrons are progressively filled in 5f-orbitals in prepenultimate shell are called actinoids. 1-14 0-1 Their general electronic configuration is, [Rn]86 5f 6d 7s²³.
(52) Coordination compound. 
 Ans. It consists of a central metal ion or atom surrounded by atoms, molecules or anions called ligands by coordinate bonds, e.g. cisplatin Pt(NH3)₂Cl₂, [Cu(NH3)4 JSO4.

 (53) Coordination sphere. 
 Ans. A coordination entity consisting of a central metal atom or ion and the coordinating groups like neutral molecules or anions (ligands) written inside a square bracket is together called coordination sphere. This is a discrete structural unit. The ionisable groups (generally ions) called counter ions are written outside the bracket. For example, in the coordination compound K₁[Fe(CN),1, the coordination sphere is [Fe(CN), while K represents counter ion. 

 (54) Ligands. 
 Ans. The neutral molecules or negatively charged anions (or rarely positive ions) which are bonded by coordinate bonds to the central metal atom or metal ion in a coordination compound are called ligands or donor groups. For example, in [Cu(CN), ], four CN ions are ligands coordinated to central metal ion Cu²+. 

 (55) Homoleptic complex.
 Ans. The complexes in which the central metal atom or ion is attached to one kind of donor groups (ligands) are called homoleptic complexes. E.g. [Co(NH3), 1³. In this complex, Co³ ion is attached to six identical donor groups like NH,. 

 (56) Heteroleptic complex. 
 Ans. The complexes in which central metal atom or ion is attached to more than one kind of donor groups (ligands) are called heteroleptic complexes. E.g. [Co(NH3),Cl₂]. In this complex, Co³ ion is attached to two kinds of ligands, namely four NH, and two Cl-. 

 (57) Linkage isomerism. 
 Ans. The phenomenon of isomerism in which the coordination compounds have the same metal atom or ion and same ligand but bonded through different donor atoms or linkages is known as linkage isomerism. 

 (58) Coordination number. 
 Ans. The number of (monodentate) ligands which are directly bonded by coordinate bonds to central metal atom or ion in a coordi nation compound is called coordination number (CN) of the metal atom or ion. 

 (59) Coordination isomerism. 
 Ans. The phenomenon of isomerism in the ionic coordination compounds having the same molecular formula but different complex ions involving the interchange of ligands between cationic and anionic entities of different metal ions is called coordination isomerism. 

 (60) Hydrate isomerism.
 Ans. The phenomenon of isomerism in the coordination compounds arising due to the exchange of H₂O molecules inside the coordination sphere and outer sphere of the complex is known as hydrate isomerism.
(61) Plane polarized light.
 Ans. A light having oscillations only in one plane perpendicular to direction of propagation of light is known as plane polirized light. 

 (62) Chiral carbon atom. 
 Ans. A carbon which is attached to four different atoms or groups is called chiral carbon ato 

 (63) Racemic mixture or Racemate. 
 Ans. A mixture containing equimolar quantities of dextro (d) and laevo (1) optical isomers which is optically inactive due to external compensation is called a racemic mixture or racemate. It is represented as (dl) or (±). 

 (64) Dextrorotatory substance or d-Isomer. 
Ans. An optically active substance (or isomer) which rotates the plane of a plane polarized light to the right hand side (RHS) is called dextrorotatory substance (or isomer) and denoted by d or (+) sign. 

 (65) Laevorotatory substance or l-Isomer. Ans. An optically active substance (or isomer) which rotates the plane of a plane polarized light to the left hand side (LHS) is called laevorotatory substance (or isomer) and denoted by / or (-) sign.
(66) Alcohols. 
 Ans. Alcohols are the hydroxy derivatives of hydrocarbons in which one or more hydrogen atoms are replaced by hydroxyl group. Examples: CH, OH methyl alcohol, CH₂-CH₂-OH ethyl alcohol. 

 (67) Phenols. 
 Ans. The hydroxy derivative of benzene in which the OH group is directly attached to benzene ring is called phenol.
(68) Aliphatic aldehydes. 
 Ans. The compounds in which the -CHO group (formyl group or aldehyde group) is attached directly to sp³ hybridized carbon atom that is saturated carbon atom are called aliphatic aldehydes. (Exception: Formaldehyde, H-CHO is also classified as aliphatic aldehyde though -CHO group is not attached to any carbon). For example: CH, – CHO CH,–CH, – CHO (Propionaldehyde) (Acetaldehyde) 

 (69) Aliphatic ketones.
 Ans. The compounds in which C=0 group is attached to two alkyl groups are called aliphatic ketones. Examples: CH₂-C-CH₁, CH₂-C-CH₂-CH₂ Acetone Ethyl methyl ketone

  (70) Aliphatic carboxylic acids. 
Ans. The organic compounds in which carboxyl (-COOH) group is bonded to an alkyl group are called aliphatic carboxylic acids or fat acids. (Exception : Formic acid, H-COOH is also classified as aliphat carboxylic acid though-COOH group is not attached to any carbon). (Acetic acid) For example: H₂C-COOH H₂C-CH₂-COOH (Propionic acid) 

 (71) Aldol condensation. 
 Ans. When aldehydes or ketones containing x-H atoms a warmed with a dilute base or dilute acid, two molecules of the undergo self condensation to give -hydroxy aldehyde (aldol) B-hydroxy ketone (ketol) respectively.
Ans. The alkyl or aryl derivatives of ammonia in which one, tv or all the three hydrogen atoms attached to nitrogen are replaced same or different alkyl or aryl groups are called amines. OR Amin are nitrogen containing organic compounds having basic character Example: methyl amine: CH, -NH₂
(73) Biomolecules. 
 Ans. The lifeless, complex organic molecules which combine in specific manner to produce life or control biological reactions a called biomolecules. Examples: Carbohydrates, lipids (fats and oils), nucleic acid enzymes. 

 (74) Carbohydrates. 
 Ans. Carbohydrates are optically active polyhydroxy aldehydes polyhydroxy ketones, or the compounds which on hydrolysis produ polyhydroxy aldehydes or polyhydroxy ketones. Examples: Glucose, sucrose, fructose.

 (75) Oligosaccharides. 
 Ans. An oligosaccharide is a carbohydrate (sugar) which hydrolysis gives two or more monosaccharide units. 

 (76) Proteins. 
 Ans. Chemically proteins are polyamides which are high molecular weight polymers of the monomer units i.e. a-amino acids. OR It can also be defined as Proteins are the biopolymers of a large number of -amino acids and they are naturally occurring polymeric nitro genous organic compounds containing 16% nitrogen and peptide linkages (-CO-NH-). 

 (77) -Amino acids. 
 Ans. -Amino acids are carboxylic acids having an amino (-NH₂) group bonded to the x-carbon i.e. the carbon next to carboxyl (-COOH) group. OR x-Amino acids are derivatives of carboxylic acids, obtained by replacing -H atom by amino group. They are bifunctional compounds containing acidic 0 and basic - NH₂ groups. OH Example: H₂N-CH-COOH R a-amino acid (z-carbon chiral) 

 (78) Peptide bond.
 Ans. Proteins are the polymers of amino acids and they are connected to each other. The bond that connects -amino acids to each other is called peptide bond (peptide linkage, - CONH- ). 

 (79) Nucleic acids. 
 Ans. Nucleic acids are unbranched polymers of repeating monomers i.e. nucleotides. In other words, nucleic acids have a polynucleotide structure which in turn consists of a base, a pentose sugar and phosphate moiety. OR Nucleic acids are bimolecules which are found in the nuclei of all living cells in the form of nucleo proteins or chromosomes. (Nucleoproteins - Proteins + Nucleic acid) (prosthetic group)
(80) Polymers. 
 Ans. Polymers are high molecular mass macromolecules (10³-107 u) and consists of repeating units of monomers.
(88) Green chemistry.
 Ans. Green chemistry is the use of chemistry for pollution prevention and it designs the use of chemical products and processes that reduce or eliminate the use or generation of hazardous substances. 

(89) Sustainable development. 
 Ans. Sustainable development is the development that meets the needs of the present, without compromising the ability of future generations to meet their own needs. 

 (90) Nanoscience. 
 Ans. The study of phenomena and manipulation of materials at atomic, molecular and macromolecular scales where properties differ significantly from those at a larger scale is called nanoscience. 

 (91) Nanotechnology. 
 Ans. The design, characterization, production and application of structures, device and system by controlling shape and size at nanometer scale is called nanotechnology.

 (92) Nanomaterial. 
 Ans. A material having structural components with at least one dimension in the nanometer scale that is 1-100 nm is called the nanomaterial. Nanomaterials are larger than single atoms but smaller than bacteria and cells. 

 (93) Nanochemistry. 
 Ans. It is the combination of chemistry and nanoscience. It deals with designing and synthesis of materials of nanoscale with different size and shape, structure and composition and their organization into functional architectures.

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