Chemistry Solved Questions and Fundamental Concepts
Solid State Chemistry
Question: Explain Schottky defect and Frenkel defect with examples.
Answer: Schottky defect is a type of point defect in which an equal number of cations and anions are missing from their lattice sites. Due to this defect, the density of the crystal decreases. Example: NaCl, KCl. Frenkel defect is a type of defect in which an ion leaves its lattice site and occupies an interstitial position. In this defect, the density of the crystal remains unchanged. Example: AgCl, ZnS.
Question: Calculate the number of atoms in FCC and BCC unit cells.
Answer: In an FCC (Face-Centered Cubic) unit cell, atoms at corners = 8 × 1/8 = 1 and atoms at face centers = 6 × 1/2 = 3. Total atoms in FCC = 4. In a BCC (Body-Centered Cubic) unit cell, atoms at corners = 8 × 1/8 = 1 and the atom at the body center = 1. Total atoms in BCC = 2.
Question: Derive the density formula of a unit cell.
Answer: Density (d) = Mass of unit cell / Volume of unit cell. Mass of unit cell = (Z × M) / NA, where Z is the number of atoms in the unit cell, M is the molar mass, and NA is Avogadro’s number. Volume of unit cell = a³. Therefore, the density formula becomes: d = (Z × M) / (a³ × NA).
Question: What are n-type and p-type semiconductors?
Answer: An n-type semiconductor is formed by doping a pure semiconductor with a pentavalent impurity such as phosphorus or arsenic. In this type, electrons are the majority charge carriers. A p-type semiconductor is formed by doping a pure semiconductor with a trivalent impurity such as boron or aluminium. In this type, holes are the majority charge carriers.
Solutions
Question: State and explain Raoult’s Law.
Answer: Raoult’s law states that the partial vapour pressure of each component of an ideal solution is directly proportional to its mole fraction in the solution. Mathematically: P₁ = X₁P₁°, where P₁ is the partial vapour pressure, X₁ is the mole fraction, and P₁° is the vapour pressure of the pure component.
Question: What are ideal and non-ideal solutions?
Answer: An ideal solution is a solution which obeys Raoult’s law at all concentrations, and no heat is absorbed or evolved during mixing. Example: Benzene and Toluene. A non-ideal solution is a solution which does not obey Raoult’s law.
Question: Explain positive and negative deviation from Raoult’s law.
Answer: Positive deviation occurs when the vapour pressure of the solution is greater than expected from Raoult’s law due to weaker intermolecular forces. Example: Ethanol and Acetone. Negative deviation occurs when the vapour pressure of the solution is lower than expected due to stronger intermolecular forces. Example: Chloroform and Acetone.
Question: Define molarity, molality, and mole fraction.
Answer: Molarity is defined as the number of moles of solute present in one litre of solution. Molality is defined as the number of moles of solute present in one kilogram of solvent. Mole fraction is defined as the ratio of moles of a component to the total moles of the solution.
Electrochemistry
Question: Write and explain the Nernst equation.
Answer: The Nernst equation gives the relationship between cell potential and the concentration of ions in a solution. It is written as: E = E° − (0.0591/n) log Q, where E is the cell potential, E° is the standard electrode potential, n is the number of electrons transferred, and Q is the reaction quotient.
Question: What is an electrochemical cell?
Answer: An electrochemical cell is a device which converts the chemical energy of a spontaneous redox reaction into electrical energy.
Question: Explain Kohlrausch’s Law of independent migration of ions.
Answer: Kohlrausch’s law states that at infinite dilution, the molar conductivity of an electrolyte is equal to the sum of the molar conductivities of the individual ions. Mathematically: Λ° = λ°₊ + λ°₋.
Question: What is corrosion? Explain the rusting of iron.
Answer: Corrosion is the slow destruction of metals due to chemical reactions with the environment. Rusting of iron occurs when iron reacts with oxygen and moisture, forming hydrated iron oxide. Reaction: 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O.
Chemical Kinetics
Question: Define order of reaction and molecularity.
Answer: Order of reaction is the sum of the powers of the concentration terms in the rate equation. Molecularity is the number of reacting molecules participating in an elementary reaction.
Question: Derive the integrated rate equation for a first-order reaction.
Answer: For a first-order reaction A → Products, the integrated rate equation is: k = (2.303/t) log (a/(a−x)), where a is the initial concentration and x is the concentration reacted at time t.
Question: What is the half-life of a first-order reaction?
Answer: The half-life of a first-order reaction is the time required for the concentration of the reactant to become half of its initial value. Formula: t½ = 0.693/k.
Question: Explain the Arrhenius equation.
Answer: The Arrhenius equation shows the effect of temperature on the rate constant. It is given by: k = A e(−Ea/RT), where k is the rate constant, A is the frequency factor, Ea is the activation energy, R is the gas constant, and T is the temperature.
Surface Chemistry
Question: What is an adsorption isotherm? Explain the Freundlich isotherm.
Answer: An adsorption isotherm is the relationship between the amount of gas adsorbed on the surface of an adsorbent and the pressure of the gas at a constant temperature. The Freundlich adsorption isotherm is an empirical relation which states that the amount of gas adsorbed per unit mass of adsorbent is proportional to the pressure of the gas raised to the power 1/n. Mathematically: x/m = kP1/n, where x is the mass of gas adsorbed, m is the mass of adsorbent, P is the pressure, and k and n are constants.
Question: Explain types of catalysis (homogeneous and heterogeneous).
Answer: Homogeneous catalysis is the type of catalysis in which the catalyst and reactants are present in the same phase. Example: Oxidation of SO₂ to SO₃ in the presence of NO gas. Heterogeneous catalysis is the type of catalysis in which the catalyst and reactants are present in different phases. Example: Hydrogenation of vegetable oil using a nickel catalyst.
Question: What are emulsions? Give examples.
Answer: Emulsions are colloidal systems in which both the dispersed phase and the dispersion medium are liquids. Example: Milk (liquid in liquid) and butter.
Electrochemistry (Extra)
Question: Define electrode potential and standard electrode potential.
Answer: Electrode potential is the tendency of an electrode to gain or lose electrons when it is in contact with its electrolyte. Standard electrode potential is the electrode potential measured under standard conditions (1 M concentration, 1 atm pressure, and 298 K temperature).
Question: Relation between ΔG and EMF of a cell.
Answer: The relation between Gibbs free energy change and the EMF of a cell is given by the equation: ΔG = −nFE, where ΔG is the change in Gibbs free energy, n is the number of electrons transferred, F is the Faraday constant, and E is the EMF of the cell.
Question: Write the electrochemical series and its importance.
Answer: The electrochemical series is the arrangement of elements in order of their standard electrode potentials. Importance: It helps to predict the feasibility of redox reactions, compare the oxidizing and reducing power of elements, and determine the direction of electron flow in electrochemical cells.
Chemical Kinetics (Continued)
Question: Difference between zero-order and first-order reactions.
Answer: In a zero-order reaction, the rate of reaction is independent of the concentration of the reactant (Rate = k). In a first-order reaction, the rate depends on the concentration of one reactant (Rate = k[A]).
Question: Graph of a first-order reaction.
Answer: In a first-order reaction, the plot of log[A] versus time gives a straight line with a negative slope equal to −k/2.303.
Question: Factors affecting the rate of reaction.
Answer: The rate of reaction depends on:
- Concentration of reactants
- Temperature
- Catalyst
- Surface area of reactants
- Nature of reactants
Coordination Compounds
Question: Define ligand and types of ligands (monodentate, bidentate).
Answer: A ligand is an atom, ion, or molecule which donates a pair of electrons to a central metal atom to form a coordinate bond. A monodentate ligand has only one donor atom. Example: NH₃, Cl⁻. A bidentate ligand has two donor atoms which can bind to the metal ion. Example: Ethylenediamine.
Question: What are double salts and coordination compounds?
Answer: Double salts are salts which dissociate completely into simple ions in solution. Example: Mohr’s salt. Coordination compounds are compounds in which a central metal atom is bonded to ligands and they do not dissociate completely in solution. Example: [Co(NH₃)₆]Cl₃.
Question: Write formulas from IUPAC names.
Answer:
- Potassium hexacyanoferrate(II) → K₄[Fe(CN)₆]
- Tetraammine copper(II) sulphate → [Cu(NH₃)₄]SO₄
Haloalkanes and Haloarenes
Question: Preparation of alkyl halides from alcohol.
Answer: Alkyl halides are prepared from alcohol by reaction with hydrogen halides (HX) such as HCl, HBr, or HI. Reaction: R–OH + HX → R–X + H₂O.
Question: Explain the Wurtz reaction.
Answer: The Wurtz reaction is the reaction in which two molecules of alkyl halides react with sodium metal in the presence of dry ether to form a higher alkane. Reaction: 2R–X + 2Na → R–R + 2NaX.
Question: Why aryl halides do not undergo nucleophilic substitution easily.
Answer: Aryl halides do not undergo nucleophilic substitution easily because the C–X bond has partial double bond character due to resonance, which makes the bond stronger and difficult to break.
Alcohols, Phenols, and Ethers
Question: Preparation of ether (Williamson synthesis).
Answer: In Williamson synthesis, ethers are prepared by the reaction of sodium alkoxide with an alkyl halide. Reaction: R–ONa + R–X → R–O–R + NaX.
Question: Why phenol is acidic.
Answer: Phenol is acidic because the phenoxide ion formed after the loss of H⁺ is stabilized by resonance.
Question: Reaction of phenol with bromine water.
Answer: Phenol reacts with bromine water to form a white precipitate of 2,4,6-tribromophenol. Reaction: C₆H₅OH + 3Br₂ → C₆H₂Br₃OH + 3HBr.
Aldehydes and Ketones
Question: Preparation of aldehydes and ketones.
Answer: Aldehydes and ketones can be prepared by the oxidation of alcohols. Primary alcohols give aldehydes and secondary alcohols give ketones.
Question: Explain Clemmensen reduction and Wolff–Kishner reduction.
Answer: Clemmensen reduction converts aldehydes or ketones into hydrocarbons using zinc amalgam and concentrated HCl. Wolff–Kishner reduction converts aldehydes or ketones into hydrocarbons using hydrazine (NH₂NH₂) and a strong base in the presence of heat.
Question: Difference between aldehyde and ketone tests.
Answer: Aldehydes give a positive Tollens’ test and Fehling’s test, producing a silver mirror or red precipitate respectively, while ketones generally do not give these tests.
Amines
Question: Basicity order of amines.
Answer: In aqueous solution, the basicity order is: Secondary amine > Primary amine > Tertiary amine > Ammonia.
Question: Diazotisation reaction of aniline.
Answer: Aniline reacts with nitrous acid (NaNO₂ + HCl) at 273–278 K to form benzene diazonium chloride. Reaction: C₆H₅NH₂ + NaNO₂ + 2HCl → C₆H₅N₂⁺Cl⁻ + NaCl + 2H₂O.
Question: Sandmeyer reaction.
Answer: The Sandmeyer reaction is the reaction in which benzene diazonium chloride is converted into chlorobenzene or bromobenzene using CuCl or CuBr as a catalyst. Reaction: C₆H₅N₂⁺Cl⁻ + CuCl → C₆H₅Cl + N₂.
Solid State (Additional Concepts)
Question: What are ionic, metallic, molecular, and covalent solids?
Answer: Ionic solids are solids in which particles are ions held together by strong electrostatic forces. Example: NaCl. Metallic solids are solids in which metal atoms are held together by metallic bonding and a sea of free electrons. Example: Copper, Iron. Molecular solids are solids in which molecules are held together by weak intermolecular forces like van der Waals forces. Example: Ice, Dry ice. Covalent solids are solids in which atoms are connected by a network of covalent bonds throughout the crystal. Example: Diamond, Silicon carbide.
Question: What is packing efficiency in crystal structures?
Answer: Packing efficiency is the percentage of space in a crystal structure that is occupied by particles. It is calculated as: Packing efficiency = (Volume occupied by particles / Total volume of unit cell) × 100.
Question: Explain imperfections in solids.
Answer: Imperfections in solids are defects present in crystal structures due to the irregular arrangement of atoms or ions. These defects may be point defects, such as the Schottky defect and Frenkel defect, which affect the physical properties of the solid.
Solutions (Additional Concepts)
Question: What are colligative properties? Name them.
Answer: Colligative properties are properties of dilute solutions which depend only on the number of solute particles and not on their nature. The four colligative properties are:
- Relative lowering of vapour pressure
- Elevation of boiling point
- Depression of freezing point
- Osmotic pressure
Question: Define relative lowering of vapour pressure.
Answer: Relative lowering of vapour pressure is the ratio of the lowering of vapour pressure of a solution to the vapour pressure of the pure solvent. Mathematically: (P° − P) / P°.
Question: What is the van’t Hoff factor (i)?
Answer: The van’t Hoff factor is the ratio of the actual number of particles present in solution after dissociation or association to the number of particles expected theoretically. i = Observed colligative property / Calculated colligative property.
Electrochemistry (Additional Concepts)
Question: Difference between a galvanic cell and an electrolytic cell.
Answer: In a galvanic cell, chemical energy is converted into electrical energy and the reaction is spontaneous. In an electrolytic cell, electrical energy is used to drive a non-spontaneous chemical reaction.
Question: What is molar conductivity?
Answer: Molar conductivity is the conductance of a solution containing one mole of electrolyte placed between two electrodes one centimeter apart. It is represented by Λm.
Question: Explain conductance and conductivity.
Answer: Conductance is the ability of a substance to allow the flow of electric current. Conductivity is the conductance of a solution placed between two electrodes with unit area and unit distance between them.
Chemical Kinetics (Additional Concepts)
Question: What is activation energy?
Answer: Activation energy is the minimum amount of energy required by reacting molecules to undergo a chemical reaction.
Question: Factors affecting the rate of reaction.
Answer: The rate of reaction is affected by the concentration of reactants, temperature, presence of a catalyst, surface area of reactants, and the nature of reactants.
Question: What is a pseudo first-order reaction? Give an example.
Answer: A pseudo first-order reaction is a reaction which is actually of a higher order but behaves like a first-order reaction because the concentration of one reactant remains constant. Example: Hydrolysis of an ester in the presence of excess water.
Surface Chemistry (Additional Concepts)
Question: What are lyophilic and lyophobic colloids?
Answer: Lyophilic colloids are solvent-loving colloids in which the dispersed phase has a strong affinity for the dispersion medium. Example: Starch sol. Lyophobic colloids are solvent-hating colloids in which the dispersed phase has little affinity for the dispersion medium. Example: Gold sol.
Question: What is coagulation of colloids?
Answer: Coagulation is the process of precipitation of colloidal particles by the addition of electrolytes which neutralize their charge.
Question: Explain the Hardy–Schulze rule.
Answer: The Hardy–Schulze rule states that the greater the valency of the ion added, the greater will be its power to cause coagulation of the colloidal solution.
d-Block Elements
Question: Why do transition metals form complex compounds?
Answer: Transition metals form complex compounds because they have a small size, high charge, and the availability of vacant d-orbitals which allow them to accept electron pairs from ligands.
Question: Why are Zn, Cd, and Hg not typical transition metals?
Answer: Zn, Cd, and Hg are not typical transition metals because they have completely filled d-orbitals in their atoms and ions, and therefore do not show the typical properties of transition elements.
Question: Explain the magnetic properties of transition metals.
Answer: Magnetic properties of transition metals arise due to the presence of unpaired electrons in d-orbitals. Compounds with unpaired electrons are paramagnetic, while those without unpaired electrons are diamagnetic.
Coordination Compounds (Additional Concepts)
Question: What is chelation?
Answer: Chelation is the formation of a coordination compound in which a multidentate ligand forms two or more coordinate bonds with the central metal ion, forming a ring structure.
Question: Difference between double salt and coordination compound.
Answer: Double salts dissociate completely into simple ions in solution. Example: Mohr’s salt. Coordination compounds retain their complex ions in solution and do not dissociate completely. Example: [Co(NH₃)₆]Cl₃.
Question: What is crystal field splitting?
Answer: Crystal field splitting is the splitting of degenerate d-orbitals of a metal ion into groups of different energy levels when ligands approach the metal ion.
Haloalkanes and Haloarenes (Additional Concepts)
Question: Preparation of alkyl halides from alkenes.
Answer: Alkyl halides are prepared from alkenes by the addition of hydrogen halides (HX) across the double bond. Reaction: CH₂=CH₂ + HCl → CH₃–CH₂Cl.
Question: What is an elimination reaction?
Answer: An elimination reaction is a reaction in which two atoms or groups are removed from adjacent carbon atoms, resulting in the formation of a double bond.
Question: Write uses of chloroform and iodoform.
Answer: Chloroform is used as a solvent and was formerly used as an anaesthetic. Iodoform is used as an antiseptic for dressing wounds.
Alcohols, Phenols, and Ethers (Additional Concepts)
Question: Preparation of alcohols from alkenes.
Answer: Alcohols are prepared from alkenes by a hydration reaction in the presence of an acid catalyst. Reaction: CH₂=CH₂ + H₂O → CH₃CH₂OH.
Question: Reaction of ethanol with sodium metal.
Answer: Ethanol reacts with sodium metal to form sodium ethoxide and hydrogen gas. Reaction: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂.
Question: Explain Kolbe’s reaction.
Answer: In Kolbe’s reaction, sodium phenoxide reacts with carbon dioxide under pressure and, on acidification, gives salicylic acid.
Aldehydes, Ketones, and Carboxylic Acids
Question: Preparation of carboxylic acids.
Answer: Carboxylic acids are prepared by the oxidation of primary alcohols or aldehydes using strong oxidizing agents such as KMnO₄ or K₂Cr₂O₇.
Question: Explain the decarboxylation reaction.
Answer: Decarboxylation is the reaction in which carboxylic acids lose carbon dioxide when heated with soda lime, forming hydrocarbons.
Question: What is the Hell–Volhard–Zelinsky reaction?
Answer: The Hell–Volhard–Zelinsky reaction is the halogenation of the α-hydrogen of carboxylic acids in the presence of red phosphorus and halogen, producing α-halo carboxylic acids.
Amines (Additional Concepts)
Question: Preparation of amines from nitro compounds.
Answer: Amines are prepared by the reduction of nitro compounds using hydrogen in the presence of a catalyst or by using reducing agents such as Sn/HCl or Fe/HCl. Reaction: C₆H₅NO₂ → C₆H₅NH₂.
Question: Difference between aliphatic and aromatic amines.
Answer: Aliphatic amines contain alkyl groups attached to nitrogen. Example: CH₃NH₂. Aromatic amines contain an aryl group attached to nitrogen. Example: Aniline (C₆H₅NH₂).
Question: Explain Gabriel phthalimide synthesis.
Answer: Gabriel phthalimide synthesis is a method for the preparation of primary amines by heating potassium phthalimide with an alkyl halide, followed by hydrolysis to give the primary amine.