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Chemistry Papers with Solution for STD. XII

• The Book contains:
  • Quick revision of the chapters
  • Papers with solutions
  • Summary of previous board questions
• The price is Rs 320
• Questions are framed in a manner that they can be asked in the upcoming exams. Hence, these are most likely questions for the examination of 2025.
• Students are advised to read this book only after finishing the text book.

Chapter-wise Distribution of Marks

• Topic Number 1: Solid State
  • Without option weightage : 3
  • With option weightage: 5
• Topic Number 2: Solutions
  • Without option weightage: 4
  • With option weightage: 6
• Topic Number 3: Ionic Equilibria
  • Without option weightage: 6
  • With option weightage: 8
• Topic Number 4: Chemical Thermodynamics
  • Without option weightage: 2
  • With option weightage: 3
• Topic Number 5: Electrochemistry
  • Without option weightage: 5
  • With option weightage: 7
• Topic Number 6: Chemical Kinetics
  • Without option weightage: 6
  • With option weightage: 9
• Topic Number 7: The Elements of Group 16, 17, and 18
  • Without option weightage: 6
  • With option weightage: 8
• Topic Number 8: Transition & Inner Transition Elements
  • Without option weightage: 6
  • With option weightage: 8
• Topic Number 9: Coordination compounds
  • Without option weightage: 5
  • With option weightage: 7
• Topic Number 10: Halogen Derivatives
  • Without option weightage: 5
  • With option weightage: 7
• Topic Number 11: Alcohols, Phenols, and Ethers
  • Without option weightage: 4
  • With option weightage: 6
• Topic Number 12: Aldehydes, Ketones and Carboxylic acids
  • Without option weightage: 6
  • With option weightage: 8
• Topic Number 13: Amines
  • Without option weightage: 3
  • With option weightage: 4
• Topic Number 14: Biomolecules
  • Without option weightage: 3
  • With option weightage: 4
• Topic Number 15: Introduction to Polymer Chemistry
  • Without option weightage: 3
  • With option weightage: 4
• Topic Number 16: Green Chemistry and Nano Chemistry
  • Without option weightage: 3
  • With option weightage: 4
• Knowledge Percentage: 30 %; Understanding Percentage: 42 %; Application and Skill Percentage: 28 %
• Easy Questions Percentage: 30 %; Average Questions Percentage: 50 % ; Difficult Questions Percentage: 20 %

Weightage as per type of questions

• Multiple Choice Questions, Number of questions: (Ten), Marks for each questions: 1 Mark each , Total Marks: 10 Marks
• Very Short Answers, Number of questions: (Eight), Marks for each questions: 1 Mark each , Total Marks: 08 Marks
• Short Answers - I, Number of questions: (Twelve), Marks for each questions: 2 Marks each , Total Marks: 24 Marks
• Short Answers - II, Number of questions: (Twelve),Marks for each questions: 3 Marks each , Total Marks: 36 Marks
• Long Answers, Number of questions: (Twelve), Marks for each questions: 4 Marks each , Total Marks: 20 Marks

SOLID STATE : Quick Revision of the Chapter

• Solids' constituent particles (atoms/ions/molecules) have a fixed arrangement and stationary position due to strong intermolecular or interatomic forces.
• Solids possess specific shape, density, volume, melting point, and boiling point.
• Solids are categorized into crystalline and amorphous based on constituent particles' orderly arrangement.

Crystalline solids

• Arrangement: particles in a repeating pattern (long range).
• Examples: NaCl, diamond, K2SO4
• Intermolecular attractions are strong.
• Melting Point: sharp.
• Anisotropy is exhibited: physical properties change when measured in different directions (e.g., refractive index, thermal/electrical conductance).

Amorphous solid

• Arrangement: constituent particles are not regularly arranged.
• Melting Point: gradually melt over a temperature range.
• Supercooled liquids: another name for amorphous solids.
• Isotropy: property where physical properties remain the same regardless of direction. When cut with a sharp-edged tool, they split irregularly (e.g., glass, tar, metallic glass).
• Isomorphism: crystalline substances with the same crystal structure (e.g., NaF/MgO, NaNO3/CaCO3, Cr2O3/Fe2O3).
• Polymorphism: a substance crystallizes in multiple forms under different conditions (e.g., calcite, aragonite; both are CaCO3 forms).
• Isotropy: amorphous solids' physical properties are identical even when measured in different directions.

Classification of Crystalline Solids

• Classified into: ionic, covalent network, molecular, and metallic.

Ionic crystals

• Made of charged ions (cations and anions) in a specific formation throughout. Held by strong electrostatic attraction (coulombic forces).
• Hard, brittle solids with high melting points.
• Non-conductive with positive and negative charges compensated; molten/aqueous states allow charge separation and conductivity.
• Distortion/fracture happen upon shearing force application examples are NaCl, K2SO4, CaF2, and KCl.

Covalent network crystals/solids

• Constituent particles are atoms.
• Atoms join by covalent bonds.
• They form a rigid, giant molecule.
• Hard and incompressible.
• High melting/boiling points.
• Poor conductors of heat/electricity due to localized, immobile electrons in covalent bonds.
• Examples include diamond, quartz (SiO2), carborundum, and boron nitride.

Molecular crystals/solids

• Formed when substances like Cl2, CH4, H2, CO2, and O2 solidify. molecules are the constituent particles.
• Intermolecular forces, such as dipole-dipole interactions, hold these molecules.
• They are soft solids with low melting points due to weak intermolecular forces.
• Poor conductors and good insulators. Examples are: H2O, HCl, SO2

Metallic crystals/solids

• Composed of atoms of the same metallic element held by metallic bonds.
• Metallic bond: attraction between metal cations and mobile electrons.
• Malleable and ductile.
• Good thermal and electrical conductivity.
• High melting and boiling points.

Crystal Structure

• Unit Cell is the smallest repeating structural unit of a crystalline solid.
• Crystal = unit cells repeated in all directions.

Lattice point

• The location at the intersection of grid lines (ions, atoms or molecules) represents constituent particles.
• Crystal lattice: the structure obtained by joining lattice points.

Types of Unit Cell

• Primitive/Simple: particles are present at the comers only.
• Body-centered: one particle at the body's center, in addition to comers particles.
• Face-centered: one particle at the center of each face, in addition to comer particles. Base-centered: particles at the center of any two opposite faces, besides comer particles.
• Unit cells have six parameters: three edges (a, b, c) and three angles (α, β, γ).
• Only 14 ways in which similar points can be arranged three dimensionally in space—Bravais lattices.

Bravais lattices

• Seven crystal structures: cubic, tetragonal, orthorhombic, rhombohedral, monoclinic, triclinic and hexagonal.

Cubic System

Simple or primitive unit

• Particles are present at the corners of the cube and each corner contributes ⅛ of constituent particles.
• One particle per unit cell.

Body-centered unit

• One particle at the cube's center, in addition to the 8 corners
• Particles per unit cell two

Face-centered unit

• 8 corners atoms + 6 face centers
• Corner atoms: contribute ⅛ to each unit cell Contribution of each atom at the face per unit cell is ½
• Four atoms make-up each unit cell

Correlation of molar mass, density, substance, and unit cell edge length.

• Volume of unit cell = a3 given 'a' as edge length.
• Mass of one particle be 'm' w/ 'n' particles per unit cell: unit cell mass = mxn.
• Density (p) of unit cell = (mxn) / a3.
• Molar mass (M) = (mxNA) / (Na) with 'm' as one particle mass, NA as Avogadro's number.

Crystal Lattice Particle Packing

• Coordination numbers: neighbor spheres that touch any given sphere.
• The number of the closest neighboring constituent particles(atoms,ions,or molecules) which are in contact with particular particle or atoms in the crystal lattice.

Close Packed Structures

• One-dimensional/linear packing: spheres placed together in a line (coordination number is 2).
• Two-dimensional close packing: generates by layering one arrangement on another.
• AAA type: spheres vertically and horizontally aligned (coordination number is 4); simple cubic structure when 3D assembled.
• ABAB type: second-row spheres placed in the depression of the first (coordination number=6); planar hexagonal packing.

3D packing

• The arrangement means that each sphere in the layer is in contact with six neighboring spheres + three spheres above and three spheres below the layer.
• Tetrahedral void forms when a triangular void of the first layer is covered by a sphere of the second layer. The coordination number is 4.
• Octahedral hole is formed when triangular voids of both layers combine. The coordination number is 6.

Packing Efficiency

• Total space percentage occupied is called packing efficiency due to the number constituent particles (cations, ions or molecules of the crystal).
• Packing efficiency = (Volume occupied by particles / Volume of unit cell) x 100

Packing in simple cubic crystals:

• Atoms are present only at the corners in simple cubic crystal
• Two atoms are in contact along the edge of unit cell
• If 'r' is the radius of an atom, a=2r
• Number of atoms per unit cell = 1
• Volume of unit cell: a3 = (2r)3 = 8r3
• Volume of one particle: (4/3)πr3
• Packing efficiency: (Volume of one atom / Volume of unit cell)* 100= 52.36%
• Empty space (voids): 100 − 52.36 = 47.64%.

Packing efficiency in body-centered cubic lattices:

• Eight atoms at eight corners and one atom at the body center.
• Total number of atoms: 2
• The atoms touch each other along the cube diagonal
• FD2 = FE2 + ED2 = a2 + a2 = 2a2 with FED = 90° (E, A, and D present in triangle FED), 'a' as edge length
• In triangle FD, FD2 + AD2 = AF2 which equals a2 + 2a2 = 3a2 where ADF = 90°
• AF = √3 a = 4r
• r = (√3/4)a Volume of sphere: (4/3)πr3
• Two spheres per unit cell:volume = (8/3)πr3 Packing efficiency: [volume by particles / total volume] * 100=68% , void = 32%

Packing of face-centered cubic lattice: Atoms in the unit cell:8 corners atoms, 6 faces atoms Number of atoms = 4 (1 from corners, 3 from faces) Atoms touch each other alongside the face diagonal: a 2√ = 4r Volume of unit cell: a3 = (2√2r )3 = 16√2 r 3 Volume occupied by the sphere =4 * (4/3)πr3 =(16/3) πr3 Packing efficiency = (Volume occupied by unit cell / Volume of unit cell) *( 100):74%,vo