Chemistry Mid-Term Paper 2025 Class 11

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Chemistry Mid-Term Paper 2025 Class 11

Chemistry Mid-Term Paper 2025 Class 11 PDF

MID-TERM EXAMINATION 2025-26 [ Chemistry ] PAPERDownload
Chemistry Mid-Term Paper 2025 Class 11

Chemistry Mid-Term Paper 2025 Class 11

1. Importance of Chemistry

  • Chemistry is the branch of science that studies the composition, structure, properties, and transformation of matter.
  • It helps in understanding:
    • Composition of substances and their changes during chemical reactions.
    • The role of chemicals in daily life — medicines, fertilizers, food preservatives, detergents, etc.
    • Industrial processes like petrochemicals, metallurgy, and polymers.
    • Environmental studies — ozone depletion, greenhouse effect, etc.

2. Laws of Chemical Combination

(i) Law of Conservation of Mass

  • Mass can neither be created nor destroyed during a chemical reaction.
  • Total mass of reactants = Total mass of products.
    Example:
    H₂ + Cl₂ → 2HCl
    (Mass of H₂ + Cl₂ = Mass of 2HCl)

(ii) Law of Definite Proportions

  • A chemical compound always contains the same elements in the same fixed ratio by mass.
    Example:
    Water (H₂O) → H:O = 1:8 by mass.

(iii) Law of Multiple Proportions

  • When two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in simple whole-number ratios.
    Example:
    CO and CO₂ → Oxygen masses ratio = 1:2.

(iv) Law of Gaseous Volumes (Gay-Lussac’s Law)

  • Gases react together in simple whole-number ratios by volume under similar conditions of temperature and pressure.
    Example:
    H₂ + Cl₂ → 2HCl
    (1 volume + 1 volume → 2 volumes)

(v) Avogadro’s Law

  • Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

3. Dalton’s Atomic Theory

  • All matter is made up of indivisible particles called atoms.
  • Atoms of the same element are identical in mass and properties.
  • Atoms cannot be created or destroyed.
  • Compounds are formed by the chemical combination of atoms in fixed ratios.
  • Chemical reactions involve rearrangement of atoms.

4. Mole Concept and Molar Mass

Mole

  • 1 mole = 6.022 × 10²³ particles (Avogadro’s number).
  • It represents atoms, molecules, ions, or electrons.

Molar Mass

  • The mass of one mole of a substance.
  • Units: g/mol
    Example:
    • 1 mole H₂O = 18 g
    • 1 mole O₂ = 32 g

Number of moles (n):

n=Given mass (g)/ Molar mass (g/mol)

Chemistry Mid-Term Paper 2025 Class 11

5. Empirical and Molecular Formula

  • Empirical formula: Shows the simplest whole-number ratio of atoms in a compound.
  • Molecular formula: Shows the actual number of atoms in one molecule.

Relationship: Molecular formula=(Empirical formula)n\text{Molecular formula} = (\text{Empirical formula})_nMolecular formula=(Empirical formula)n​

where n=Molar mass/Empirical formula mass

Example:
Empirical formula = CH₂
Molar mass = 56
Empirical formula mass = 14
⇒ n = 4
⇒ Molecular formula = C₄H₈

6. Stoichiometry and Limiting Reagent

Stoichiometry

  • It deals with quantitative relationships between reactants and products in a chemical reaction.

Example: 2H2+O2→2H2O

  • 2 moles of H₂ react with 1 mole of O₂ to form 2 moles of H₂O.

Limiting Reagent

  • The reactant that is completely consumed first and limits the amount of product formed.

Example:
If 5 mol H₂ react with 2 mol O₂:
According to reaction, 2 mol H₂ needs 1 mol O₂.
For 5 mol H₂, O₂ required = 2.5 mol.
Available O₂ = 2 mol → Limiting reagent = O₂.

7. Percentage Composition

Percentage of element=Mass of element in 1 mol compound/Molar mass of compound×100

Example:
Find % of H and O in H₂O.
Molar mass = 18 g
H = 2 g, O = 16 g
%H = (2/18) × 100 = 11.11%
%O = (16/18) × 100 = 88.89%

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