Interactive ICSE Chemistry Notes - Class IX

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Table of Contents (Class IX)

1. The Language of Chemistry
Master symbols, valencies, formulae writing, equation balancing, and basic calculations (RAM, RMM, % Composition).
Quick Links: Symbols/Valency Radicals/Formulae Equations RAM/RMM/% Comp Practice Micro Tests
1.1 Symbols and Valency
Key Points:
  • Symbol: Short-hand representation (e.g., H, O, Na). Learn common ones.
  • Valency: Combining capacity.
    • Based on H atoms combined/displaced.
    • Based on Valence Electrons (e⁻) lost/gained/shared for stable octet/duplet.
    • Metals: Lose e⁻ (Valency = +ve charge, e.g., Na⁺ valency 1).
    • Non-metals: Gain/Share e⁻ (Valency = -ve charge or 8 - valence e⁻, e.g., Cl⁻ valency 1).
  • Variable Valency: Some elements show >1 valency (e.g., Fe²⁺/Fe³⁺, Cu⁺/Cu²⁺). Use Roman numerals or -ous/-ic suffix.
  • Examples: Mono (H, Na, Cl), Di (O, Mg, Ca), Tri (Al, N), Tetra (C, Si).

Critical Concept Check: Why do elements combine? How is valency determined electronically?

A: To achieve stable noble gas electron configuration (octet/duplet). Valency = number of electrons lost, gained, or shared to attain this stability.
Q: Valency of Magnesium (Mg, At No 12)?
A: Config: 2,8,2. Loses 2 e⁻ for octet. Valency = 2 (+2).
1.2 Radicals and Chemical Formulae
Key Points:
  • Radical (Polyatomic Ion): Group of atoms acting as a unit with a charge (e.g., NH₄⁺, OH⁻, SO₄²⁻, CO₃²⁻, NO₃⁻, PO₄³⁻). Memorize common ones.
  • Chemical Formula: Symbolic representation of a molecule/formula unit.
  • Writing Formulae (Criss-Cross Method):
    1. Write symbols/radicals (positive first).
    2. Write valencies above.
    3. Interchange valencies as subscripts (simplify ratio, ignore signs).
    4. Use parentheses for radicals if subscript > 1.
    Example: Aluminium Sulphate → Al³⁺ SO₄²⁻ → Al₂(SO₄)₃

Critical Concept Check: Difference between H₂O and 2H₂O?

A: H₂O = 1 molecule (2 H atoms, 1 O atom). 2H₂O = 2 separate molecules. Subscript = atoms in molecule, Coefficient = number of molecules.
Q: Formula for Calcium Phosphate (Ca=2, PO₄=3)?
A: Ca²⁺ PO₄³⁻ → Ca₃(PO₄)₂
1.3 Chemical Equations
Key Points:
  • Chemical Equation: Symbolic representation of a reaction (Reactants → Products).
  • Balancing: Obeys Law of Conservation of Mass (atoms conserved). Adjust coefficients (numbers before formulae), NOT subscripts.
  • Method (Hit & Trial): Balance metals → non-metals → H → O. Balance polyatomic ions as units if unchanged.
  • Info Conveyed: Reactants, products, stoichiometry, states (s, l, g, aq), conditions (Δ, catalyst).

Critical Concept Check: Why balance equations?

A: To reflect Law of Conservation of Mass (atoms constant), match experiment, provide correct mole ratios for calculations.
Q: Balance: Fe + H₂O → Fe₃O₄ + H₂
A: 3Fe + 4H₂O → Fe₃O₄ + 4H₂
1.4 RAM, RMM & Percentage Composition
Key Points:
  • RAM (Relative Atomic Mass): Average mass of an atom vs 1/12th mass of C-12 atom. Ratio, no units (or amu). Value reflects isotopic abundance.
  • RMM (Relative Molecular Mass): Sum of RAMs of all atoms in a molecule/formula unit. Ratio, no units. Calc: Σ(Subscript × RAM). E.g., H₂SO₄ = (2×1) + (1×32) + (4×16) = 98.
  • Percentage Composition: % by mass of each element. Formula: % Element = (Total mass of element / RMM) × 100%. E.g., % S in H₂SO₄ = (32/98)×100 ≈ 32.65%.

Critical Concept Check: Why isn't RAM always a whole number?

A: Because most elements exist as a mixture of isotopes with different masses. RAM is the weighted average mass considering the natural abundance of these isotopes (e.g., Cl ≈ 35.5 due to ³⁵Cl and ³⁷Cl).
Q: RMM of CaCO₃? (Ca=40, C=12, O=16)
A: RMM = (1×40) + (1×12) + (3×16) = 40 + 12 + 48 = 100.
Try Yourselves - Chapter 1

1. Symbol of Potassium?

2. Valency of Sulphur in H₂S?

3. Formula of Magnesium Nitrate?

4. Balance: N₂ + H₂ → NH₃

5. RMM of NaOH? (Na=23, O=16, H=1)

6. % of Oxygen in NaOH?

7. Define Radical.

8. Define RAM.

Micro Tests - Chapter 1
Micro Test 1.1 (Symbols & Valency - 10 Marks)

Test 1.1

Time: 10 Min

Answer all questions.

  1. 1. Symbol for Copper? State its variable valencies.[2]
  2. 2. Symbol & Valency of Hydroxide radical?[2]
  3. 3. Symbol & Valency of Phosphate radical?[2]
  4. 4. Define valency based on Hydrogen combination.[2]
  5. 5. What is the valency of Nitrogen in Ammonia (NH₃)?[2]
Micro Test 1.2 (Formula Writing - 10 Marks)

Test 1.2

Time: 10 Min

Write the chemical formulae for:

  1. 1. Sodium Oxide (Na=1, O=2)[2]
  2. 2. Aluminium Hydroxide (Al=3, OH=1)[2]
  3. 3. Magnesium Nitride (Mg=2, N=3)[2]
  4. 4. Calcium Bicarbonate (Ca=2, HCO₃=1)[2]
  5. 5. Iron(III) Sulphate (Fe=3, SO₄=2)[2]
Micro Test 1.3 (Equation Balancing - 10 Marks)

Test 1.3

Time: 10 Min

Balance the following equations.

  1. 1. H₂ + Cl₂ → HCl[2]
  2. 2. Mg + O₂ → MgO[2]
  3. 3. CaCO₃ + HCl → CaCl₂ + H₂O + CO₂[2]
  4. 4. Fe₂O₃ + C → Fe + CO[2]
  5. 5. Pb(NO₃)₂ → PbO + NO₂ + O₂[2]
Micro Test 1.4 (RAM/RMM/% Comp - 10 Marks)

Test 1.4

Time: 12 Min

RAM: H=1, C=12, O=16, S=32, Na=23.

  1. 1. Define Relative Atomic Mass (RAM).[2]
  2. 2. Calculate RMM of Sodium Carbonate (Na₂CO₃).[3]
  3. 3. Calculate RMM of Sulphuric Acid (H₂SO₄).[2]
  4. 4. Calculate the percentage of Carbon in Na₂CO₃.[3]
2. Chemical Changes and Reactions
Focus on identifying the four main types of chemical reactions with balanced equations and understanding energy changes (exothermic/endothermic).
2.1 Types of Chemical Changes/Reactions
Key Points: (Learn definitions and examples with balanced equations)
  • 1. Direct Combination (Synthesis): A + B → AB (e.g., 2Mg + O₂ → 2MgO; NH₃ + HCl → NH₄Cl)
  • 2. Decomposition: AB → A + B (e.g., CaCO₃
  • 3. Displacement (Single Replacement): A + BC → AC + B (A > B reactivity) (e.g., Zn + CuSO₄ → ZnSO₄ + Cu)
  • 4. Double Decomposition (Double Replacement): AB + CD → AD + CB (Exchange ions). Often forms precipitate (AgNO₃ + NaCl → AgCl↓ + NaNO₃) or water (Neutralization: NaOH + HCl → NaCl + H₂O).

Critical Concept Check: How to predict if displacement occurs?

A: Use metal reactivity series. A higher metal displaces a lower metal from its salt solution (e.g., Zn > Cu, so Zn displaces Cu from CuSO₄).
Q: Classify: Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s)↓ + 2KNO₃(aq)
A: Double Decomposition (Precipitation).
2.2 Energy Changes in Chemical Reactions
Key Points:
  • Exothermic: Releases energy (usually heat, ΔH -ve). Surroundings get warmer. Examples: Combustion, respiration, neutralization, bond formation.
  • Endothermic: Absorbs energy (usually heat, ΔH +ve). Surroundings get cooler. Examples: Photosynthesis, CaCO₃ decomp., dissolving NH₄Cl, bond breaking.
  • Energy forms: Heat, Light (photochemical), Electricity (electrochemical).

Critical Concept Check: Bond breaking vs. bond forming: Exo or Endo?

A: Bond Breaking → requires energy → Endothermic. Bond Forming → releases energy → Exothermic. Overall reaction type depends on net energy change.
Q: Burning wood: Exo or Endo?
A: Exothermic (releases heat and light).
Try Yourselves - Chapter 2

1. Classify: H₂ + Cl₂ → 2HCl

2. Classify: 2AgBr → 2Ag + Br₂

3. Classify: Mg + 2HCl → MgCl₂ + H₂

4. Classify: BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl

5. Give example of endothermic reaction.

6. Give example of exothermic reaction.

7. What type of reaction is Neutralization?

8. Which reaction type uses reactivity series?

Micro Tests - Chapter 2
Micro Test 2.1 (Reaction Types - ID - 10 Marks)

Test 2.1

Time: 8 Min

Classify the following reactions:

  1. 1. 2H₂O₂ → 2H₂O + O₂[2]
  2. 2. CaO + H₂O → Ca(OH)₂[2]
  3. 3. Fe + CuSO₄ → FeSO₄ + Cu[2]
  4. 4. FeCl₃ + 3NaOH → Fe(OH)₃↓ + 3NaCl[2]
  5. 5. Neutralization (e.g., acid + base).[2]
Micro Test 2.2 (Reaction Types - Examples - 10 Marks)

Test 2.2

Time: 10 Min

Give one balanced equation example for each:

  1. 1. Thermal Decomposition[2.5]
  2. 2. Displacement of H₂ from water by metal[2.5]
  3. 3. Precipitation (Double Decomposition)[2.5]
  4. 4. Direct Combination of two elements[2.5]
Micro Test 2.3 (Energy Changes - Definitions & Examples - 10 Marks)

Test 2.3

Time: 8 Min

Answer the following.

  1. 1. Define Exothermic Reaction.[2]
  2. 2. Define Endothermic Reaction.[2]
  3. 3. Give one example of an exothermic reaction.[2]
  4. 4. Give one example of an endothermic reaction.[2]
  5. 5. Is bond formation generally exothermic or endothermic?[2]
Micro Test 2.4 (Energy/Reaction Types - Mixed - 10 Marks)

Test 2.4

Time: 8 Min

Answer the following.

  1. 1. Decomposition of water by electricity: Exo or Endo?[2]
  2. 2. Reaction type involving exchange of ions?[2]
  3. 3. What reaction type typically requires heat/light/electricity?[2]
  4. 4. Name the reaction type: A + B → AB.[2]
  5. 5. Is dissolving NaOH in water exothermic or endothermic?[2]
3. Water
Understand water's solvent properties, solubility, hydrated/anhydrous substances, related phenomena, and water hardness.
3.1 Water as a Universal Solvent
Key Points:
  • Universal Solvent: Due to polar nature (δ+ H, δ- O), dissolves many ionic & polar covalent substances.
  • Solution: Homogeneous mixture (Solute + Solvent).
  • Solubility: Max solute in given solvent at specific temp.
  • Saturated Solution: Max solute dissolved. Unsaturated: Can dissolve more.
  • Temp Effect on Solubility (Solids in Water): Usually increases (KNO₃), some little change (NaCl), few decrease (CaSO₄).

Critical Concept Check: Saturated NaCl solution at 20°C. Heat to 50°C? Cool to 10°C?

A: Heat: Becomes unsaturated (solubility increases slightly). Cool: Becomes supersaturated → excess NaCl crystallizes out.
Q: CaSO₄ solubility decreases with temp ↑. Is dissolving Exo or Endo?
A: Exothermic (dissolving releases heat).
3.2 Hydrated/Anhydrous Substances & Properties
Key Points:
  • Water of Crystallisation: Fixed H₂O molecules in crystal structure (e.g., CuSO₄·5H₂O).
  • Hydrated Substance: Contains W.O.C (e.g., CuSO₄·5H₂O Blue Vitriol).
  • Anhydrous Substance: W.O.C removed (e.g., CuSO₄ white powder).
  • Efflorescence: Hydrated salt loses W.O.C to air (e.g., Na₂CO₃·10H₂O → powder). Occurs if V.P. hydrate > V.P. air.
  • Deliquescence: Absorbs moisture from air & dissolves (e.g., NaOH, CaCl₂). Occurs if V.P. substance < V.P. air.
  • Hygroscopy: Absorbs moisture without dissolving (e.g., conc. H₂SO₄, CaO). Used as drying agents.

Critical Concept Check: Why keep CaCl₂ sealed?

A: It's deliquescent. Absorbs atmospheric moisture → forms solution, unusable as solid.
Q: Heating blue CuSO₄·5H₂O? Colour change? Property?
A: Turns white (forms anhydrous CuSO₄). Shows existence of hydrated/anhydrous substances.
3.3 Soft Water and Hard Water
Key Points:
  • Soft Water: Lathers easily with soap (e.g., rain water).
  • Hard Water: Forms scum (precipitate) with soap. Contains dissolved Ca²⁺/Mg²⁺ salts.
  • Causes:
    • Temporary: Bicarbonates [Ca(HCO₃)₂, Mg(HCO₃)₂].
    • Permanent: Chlorides/Sulphates (CaCl₂, MgSO₄ etc.).
  • Removal:
    • Temporary: Boiling (Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂).
    • Both Types: Add Washing Soda (Na₂CO₃) → precipitates CaCO₃/MgCO₃ (e.g., CaCl₂ + Na₂CO₃ → CaCO₃↓ + 2NaCl).
  • Pros/Cons: Soft saves soap, better for boilers. Hard tastes better, provides minerals, but forms scale, wastes soap. Detergents work in hard water.

Critical Concept Check: Why detergents better than soap in hard water?

A: Soap forms insoluble scum with Ca²⁺/Mg²⁺. Detergent's Ca/Mg salts are soluble, so no scum forms; cleaning is effective.
Q: Name a chemical causing permanent hardness.
A: Calcium Sulphate (CaSO₄) or Magnesium Chloride (MgCl₂) or similar.
3.4 Drying and Dehydrating Agents
Key Points:
  • Drying Agent (Desiccant): Absorbs moisture (H₂O vapour) without chemical reaction. Often hygroscopic (e.g., conc. H₂SO₄, anhyd. CaCl₂, CaO, P₂O₅).
  • Dehydrating Agent: Removes chemically combined water (elements H & O) from compounds (e.g., conc. H₂SO₄ chars sugar: C₁₂H₂₂O₁₁ → 12C + 11H₂O).
  • Note: Conc. H₂SO₄ is both.

Critical Concept Check: Difference between drying and dehydration?

A: Drying removes physically adsorbed/absorbed moisture (like water vapour). Dehydration removes chemically bound water molecules or the elements of water (H and O) from within a compound's structure.
Q: Can conc. H₂SO₄ dry NH₃ gas? Why?
A: No. Basic NH₃ reacts chemically with acidic H₂SO₄ (2NH₃ + H₂SO₄ → (NH₄)₂SO₄). Use basic CaO instead.
Try Yourselves - Chapter 3

1. Define Saturated Solution.

2. Formula of Blue Vitriol?

3. Give example of efflorescent salt.

4. Give example of deliquescent substance.

5. Cause of temporary hardness?

6. How to remove temporary hardness?

7. How to remove permanent hardness?

8. Name a common drying agent.

Micro Tests - Chapter 3
Micro Test 3.1 (Solubility & Solutions - 10 Marks)

Test 3.1

Time: 8 Min

Answer the following.

  1. 1. Why is water called a universal solvent?[2]
  2. 2. Define a saturated solution.[2]
  3. 3. How does temp generally affect solubility of solids like KNO₃?[2]
  4. 4. How does temp affect solubility of CaSO₄?[2]
  5. 5. Name a solute whose solubility changes little with temp.[2]
Micro Test 3.2 (Hydrates & Properties - 10 Marks)

Test 3.2

Time: 10 Min

Define/Identify:

  1. 1. Water of Crystallisation.[2]
  2. 2. Efflorescence. Give example.[3]
  3. 3. Deliquescence. Give example.[3]
  4. 4. Hygroscopy. Give example.[2]
Micro Test 3.3 (Water Hardness - ID & Causes - 10 Marks)

Test 3.3

Time: 8 Min

Answer the following.

  1. 1. How does hard water react with soap?[2]
  2. 2. Name the two main ions causing hardness.[2]
  3. 3. Name the type of salt causing temporary hardness.[2]
  4. 4. Give formula of one salt causing temporary hardness.[2]
  5. 5. Name the types of salt causing permanent hardness.[2]
Micro Test 3.4 (Water Hardness - Removal & Agents - 10 Marks)

Test 3.4

Time: 10 Min

Answer the following.

  1. 1. How is temporary hardness removed by physical means?[2]
  2. 2. Write eq for removal of temp hardness by boiling (using Mg salt).[2]
  3. 3. What chemical is added to remove permanent hardness?[2]
  4. 4. Write eq for removing CaCl₂ hardness with washing soda.[2]
  5. 5. Name one drying agent mentioned in the chapter.[1]
  6. 6. Name one dehydrating agent mentioned.[1]
4. Atomic Structure and Chemical Bonding
Understand atom structure, electron arrangement, isotopes, and electrovalent/covalent bond formation (with orbit diagrams).
4.1 Structure of the Atom & Isotopes
Key Points:
  • Atom: Smallest particle of element in reactions.
  • Subatomic Particles: Proton (p⁺, +1, mass 1, nucleus), Neutron (n⁰, 0, mass 1, nucleus), Electron (e⁻, -1, negligible mass, shells).
  • Nucleus: Central, contains p⁺ & n⁰.
  • Atomic Number (Z): No. of p⁺. Defines element. Z = p⁺ = e⁻ (neutral atom).
  • Mass Number (A): No. of p⁺ + n⁰.
  • Notation: AXZ (e.g., 23Na11).
  • Isotopes: Same Z, different A (different n⁰). Examples: H (¹H, ²H, ³H), C (¹²C, ¹³C, ¹⁴C), Cl (³⁵Cl, ³⁷Cl). Same chemical properties.

Critical Concept Check: Ion X²⁺ has 10 e⁻, 12 n⁰. Identify X, state Mass Number.

A: Lost 2 e⁻. Neutral X had 10+2=12 e⁻. So, p⁺=12 (Z=12). Element is Mg. A = p⁺ + n⁰ = 12+12=24. X=Mg, A=24.
Q: Protons, electrons, neutrons in ³⁷Cl (Z=17)?
A: p⁺=17, e⁻=17, n⁰=37-17=20.
4.2 Electron Distribution & Chemical Activity
Key Points:
  • Shells (Energy Levels): K, L, M, N... (n=1, 2, 3, 4...).
  • Distribution Rule (2n²): K=2, L=8, M=18... Outermost ≤ 8 (Octet Rule). Penultimate ≤ 18.
  • Valence Shell: Outermost shell. Valence Electrons: e⁻ in valence shell.
  • Octet/Duplet Rule: Atoms tend to achieve 8 (or 2 for H, Li) valence e⁻ for stability (like noble gases) via bonding.
  • Chemical Activity: Due to tendency to complete valence shell. Noble gases are inert (stable config).

Critical Concept Check: Why Na(2,8,1) loses 1 e⁻, while Cl(2,8,7) gains 1 e⁻?

A: Na losing 1 e⁻ is easier (achieves stable 2,8 octet) than gaining 7. Cl gaining 1 e⁻ is easier (achieves stable 2,8,8 octet) than losing 7.
Q: Config of Argon (Z=18)? Active?
A: Config: 2, 8, 8. Complete octet, stable, chemically inactive.
4.3 Electrovalent (Ionic) Bonding
Key Points:
  • Formation: Transfer of e⁻ from metal (forms Cation +ve) to non-metal (forms Anion -ve).
  • Bond: Electrostatic attraction between opposite ions.
  • Conditions: Large electronegativity difference.
  • Structure: Crystal lattice (not discrete molecules). Formula = simplest ratio (formula unit).
  • Orbit Structure Examples: NaCl, MgCl₂, CaO (Practice drawing electron transfer).

Critical Concept Check: Do ionic compounds exist as molecules?

A: No. Form crystal lattice. Formula (e.g., NaCl) is simplest ratio (formula unit), not discrete molecule.
Q: Show ion formation: Mg + O.
A: Mg(2,8,2) → Mg²⁺(2,8) + 2e⁻
O(2,6) + 2e⁻ → O²⁻(2,8)
4.4 Covalent Bonding
Key Points:
  • Formation: Mutual sharing of e⁻ pairs between non-metals to achieve stable octet/duplet.
  • Bond Types: Single (1 pair shared, e.g., H₂), Double (2 pairs, e.g., O₂), Triple (3 pairs, e.g., N₂).
  • Orbit Structure Examples: H₂, Cl₂, O₂, N₂, HCl, H₂O, NH₃, CH₄, CCl₄ (Practice electron dot/Lewis structures).

Critical Concept Check: Why C(2,4) forms covalent, not ionic bonds?

A: Losing/gaining 4 e⁻ requires too much energy. Sharing 4 e⁻ is energetically favourable to achieve octet.
Q: Draw dot structure for Ammonia (NH₃).
A: N(5 valence e⁻) shares 1 pair with each of 3 H atoms. N has 1 lone pair. Structure: 
  H .. H : N : H ..
(Dots represent valence electrons; N completes octet, H completes duplet).
Try Yourselves - Chapter 4

1. Particles in nucleus?

2. Define Atomic Number.

3. Define Isotopes.

4. Elec config of Ca (Z=20)?

5. Why are noble gases stable?

6. Bond type in NaCl?

7. Bond type in H₂O?

8. Draw dot structure for Cl₂.

Micro Tests - Chapter 4
Micro Test 4.1 (Atomic Structure Basics - 10 Marks)

Test 4.1

Time: 10 Min

Answer the following.

  1. 1. Charge & Location of Proton?[2]
  2. 2. Define Atomic Number (Z).[2]
  3. 3. How many electrons in Na⁺ (Z=11)?[2]
  4. 4. Define Isotopes with an example.[3]
  5. 5. What is the max number of electrons in the L shell (n=2)?[1]
Micro Test 4.2 (Electron Config & Activity - 10 Marks)

Test 4.2

Time: 10 Min

Answer the following.

  1. 1. Write electronic configuration of P (Z=15).[2]
  2. 2. How many valence electrons in P?[1]
  3. 3. State the Octet Rule.[2]
  4. 4. Why are Noble gases (Gp 18) unreactive?[2]
  5. 5. An element has config 2,8,6. Is it likely a metal or non-metal? Why?[3]
Micro Test 4.3 (Ionic Bonding - 10 Marks)

Test 4.3

Time: 10 Min

Answer the following.

  1. 1. Define Electrovalent (Ionic) Bond.[2]
  2. 2. Show the electron transfer during formation of NaCl (Na=2,8,1; Cl=2,8,7).[3]
  3. 3. What type of elements typically form ionic bonds?[2]
  4. 4. What force holds ions together in an ionic compound?[1]
  5. 5. Show ion formation for Ca (2,8,8,2) reacting.[2]
Micro Test 4.4 (Covalent Bonding - 10 Marks)

Test 4.4

Time: 12 Min

Answer the following.

  1. 1. Define Covalent Bond.[2]
  2. 2. Draw electron dot structure for Methane (CH₄). (C=2,4; H=1)[3]
  3. 3. Draw electron dot structure for Chlorine molecule (Cl₂). (Cl=2,8,7)[3]
  4. 4. What type of bond (single/double/triple) exists in Oxygen (O₂)?[1]
  5. 5. What type of elements typically form covalent bonds?[1]
5. The Periodic Table
Understand historical development, Modern Periodic Law/Table basis, and characteristics of key groups (1, 2, 17, 18).
5.1 Early Attempts at Classification
Key Points:
  • Need: Systematize study.
  • Dobereiner's Triads (1829): Groups of 3 similar elements; middle atomic mass ≈ average of others (e.g., Li, Na, K). Limited scope.
  • Newlands' Law of Octaves (1864): Properties repeat every 8th element (like music) when arranged by atomic mass. Failed after Ca.
  • Mendeleev's Periodic Table (1869):
    • Law: Properties periodic function of atomic *masses*.
    • Merits: Systematic, predicted elements (Ga, Ge), corrected masses.
    • Demerits: H position, Isotopes, Anomalous pairs (Ar/K, Co/Ni).

Critical Concept Check: Significance of Mendeleev's predictions?

A: Showed predictive power & validity of his periodic system. Discovery of Ga/Ge matching predictions boosted acceptance.
Q: State Newlands' Law of Octaves.
A: Arranged by atomic mass, properties of 8th element repeat the 1st.
5.2 Modern Periodic Law and Table
Key Points:
  • Moseley (1913): Atomic Number (Z = no. protons) is fundamental property.
  • Modern Periodic Law: Properties periodic function of atomic *numbers*.
  • Modern Periodic Table (Long Form): Elements arranged by increasing Z.
    • Periods (7): Horizontal rows. Period no. = no. of shells being filled.
    • Groups (18): Vertical columns. Same group → same valence e⁻ → similar chemical properties.
  • Advantages: Resolves Mendeleev's issues (isotopes, anomalous pairs).
  • Structure: s, p, d, f blocks (general idea).

Critical Concept Check: How does Modern Law explain periodicity?

A: Properties depend on valence e⁻ config. Config repeats periodically as Z increases. Hence properties repeat.
Q: Element Z=11. Group? Period?
A: Config: 2,8,1. Valence e⁻=1 → Group 1. Shells=3 → Period 3.
5.3 Overview of Specific Groups
Key Points:
  • Group 1 (Alkali Metals): Li, Na, K... Soft, highly reactive metals. 1 valence e⁻ → +1 ions. Good reducing agents.
  • Group 2 (Alkaline Earth Metals): Be, Mg, Ca... Reactive metals (less than Gp 1). 2 valence e⁻ → +2 ions.
  • Group 17 (Halogens): F, Cl, Br, I... Highly reactive non-metals. 7 valence e⁻ → -1 ions (halides). Diatomic (F₂, Cl₂). Good oxidizing agents.
  • Group 18 (Noble Gases/Inert Gases): He, Ne, Ar... Gases, very unreactive. Stable config (duplet/octet). Monoatomic.

Critical Concept Check: Why reactivity ↑ down Gp 1, but ↓ down Gp 17?

A: Gp 1: React by losing e⁻. Down group, easier to lose outer e⁻ (larger size, shielding) → reactivity ↑. Gp 17: React by gaining e⁻. Down group, harder to attract incoming e⁻ (larger size, weaker attraction) → reactivity ↓.
Q: Most reactive non-metal? Group?
A: Fluorine (F). Group 17.
Try Yourselves - Chapter 5

1. Basis of Mendeleev's table?

2. Basis of Modern table?

3. Who proposed atomic number basis?

4. How many groups in Modern Table?

5. How many periods?

6. Name for Group 1 elements?

7. Name for Group 17 elements?

8. Name for Group 18 elements?

Micro Tests - Chapter 5
Micro Test 5.1 (Historical Development - 10 Marks)

Test 5.1

Time: 10 Min

Answer the following.

  1. 1. State Dobereiner's Law of Triads.[2]
  2. 2. State Newlands' Law of Octaves.[2]
  3. 3. State Mendeleev's Periodic Law.[2]
  4. 4. Give one merit of Mendeleev's Table.[2]
  5. 5. Give one demerit of Mendeleev's Table.[2]
Micro Test 5.2 (Modern Table Structure - 10 Marks)

Test 5.2

Time: 8 Min

Answer the following.

  1. 1. State the Modern Periodic Law.[2]
  2. 2. What is the basis for arranging elements in the modern table?[1]
  3. 3. How many Periods are there?[1]
  4. 4. How many Groups are there?[1]
  5. 5. What does the Period number signify?[2]
  6. 6. What is common to elements in the same Group?[3]
Micro Test 5.3 (Specific Groups - Names & Valency - 10 Marks)

Test 5.3

Time: 8 Min

Answer the following.

  1. 1. Special name for Group 1 elements?[1]
  2. 2. Number of valence electrons in Group 1?[1]
  3. 3. Special name for Group 2 elements?[1]
  4. 4. Common valency shown by Group 2 elements?[1]
  5. 5. Special name for Group 17 elements?[1]
  6. 6. Number of valence electrons in Group 17?[1]
  7. 7. Special name for Group 18 elements?[1]
  8. 8. Why are Group 18 elements generally unreactive?[3]
Micro Test 5.4 (Specific Groups - Properties - 10 Marks)

Test 5.4

Time: 8 Min

Answer the following.

  1. 1. Are Alkali Metals reactive or unreactive?[1]
  2. 2. Are Halogens metals or non-metals?[1]
  3. 3. How do Halogens exist naturally (e.g., Cl)?[2]
  4. 4. Are Alkaline Earth Metals more or less reactive than Alkali Metals?[2]
  5. 5. What type of ion do Halogens typically form?[2]
  6. 6. How do Noble Gases exist naturally (atomic state)?[2]
6. Study of the First Element - Hydrogen
Understand Hydrogen's unique position, prep methods (equations!), lab prep, Bosch process, and basic redox concepts.
6.1 Position in Periodic Table & Properties
Key Points:
  • Unique Position: Resembles Gp 1 (1 valence e⁻, forms H⁺) & Gp 17 (diatomic H₂, forms H⁻ hydride). Often placed separately.
  • Properties: Colourless, odourless gas. Lightest. Insoluble in water. Burns with pop sound (→ H₂O). Good reducing agent (e.g., CuO + H₂ → Cu + H₂O).

Critical Concept Check: Why H⁺ usually forms with non-metals, H⁻ with metals?

A: Non-metals are more electronegative, pull e⁻ pair from H → H forms H⁺. Active metals are less electronegative, H pulls e⁻ → H forms H⁻ (hydride).
Q: One reason H resembles Halogens?
A: Forms diatomic molecule (H₂). / Forms H⁻ anion.
6.2 Preparation of Hydrogen (General Methods)
Key Points: (Balanced equations essential)
  • From Water:
    • Cold Water: Active metals (Na, K, Ca). 2Na + 2H₂O → 2NaOH + H₂
    • Hot Water: Mg. Mg + 2H₂O(hot) → Mg(OH)₂ + H₂
    • Steam: Mod. active metals (Al, Zn, Fe). Zn + H₂O(g) → ZnO + H₂; 3Fe + 4H₂O(g) ⇌ Fe₃O₄ + 4H₂
    • Steam + Carbon: C + H₂O(g) → CO + H₂ (Water Gas)
  • From Dilute Acids (HCl, H₂SO₄): Metals above H in reactivity series. Zn + H₂SO₄ → ZnSO₄ + H₂. (Not HNO₃).
  • From Alkalis (NaOH, KOH): Amphoteric metals (Zn, Al, Pb). Zn + 2NaOH → Na₂ZnO₂ + H₂

Critical Concept Check: Why is Fe + Steam reversible?

A: Products can react back: H₂ passed over hot Fe₃O₄ reduces it back to Fe + H₂O. Direction depends on conditions.
Q: Balanced eq: Ca + cold water?
A: Ca + 2H₂O → Ca(OH)₂ + H₂
6.3 Laboratory Preparation of Hydrogen
Key Points:
  • Reactants: Granulated Zinc + Dilute H₂SO₄ (or HCl).
  • Why Granulated Zn? Impurity (Cu) acts as catalyst. Pure Zn reacts slowly.
  • Why Dilute Acid? Conc. acids cause side reactions (SO₂ from H₂SO₄) or are volatile (HCl). HNO₃ oxidizes H₂.
  • Apparatus: Woulfe's bottle/flask, thistle funnel (dipped below acid), delivery tube.
  • Equation: Zn + H₂SO₄(dil) → ZnSO₄ + H₂↑
  • Collection: Downward displacement of water (H₂ is nearly insoluble).
  • Precautions: No flame nearby (explosive H₂/air mix). Thistle funnel end below acid.

Critical Concept Check: Why collect over water, not air?

A: Ensures purer gas (displaces air from setup). Easy to visualize collection. Avoids rapid diffusion into air if upward delivery used.
Q: Lab collection method for H₂? Reason?
A: Downward displacement of water. Reason: H₂ is nearly insoluble in water.
6.4 Industrial Manufacture (Bosch Process)
Key Points:
  • Step 1: Water Gas Production: Steam over red-hot coke (~1000°C). C(s) + H₂O(g) → (CO(g) + H₂(g))
  • Step 2: Water-Gas Shift Reaction: Water gas + steam over Fe₂O₃/Cr₂O₃ catalyst (~450°C). CO oxidized to CO₂. (CO + H₂) + H₂O(g) → CO₂(g) + 2H₂(g)
  • Step 3: CO₂ Removal: Dissolve in water under pressure or scrub with KOH solution (2KOH + CO₂ → K₂CO₃ + H₂O).
  • Step 4: CO Removal: Absorb in ammoniacal CuCl solution.
  • Pure H₂ remains.

Critical Concept Check: Why convert CO to CO₂ in Step 2?

A: 1) Produces more H₂. 2) CO₂ is easier/cheaper to remove than CO on large scale.
Q: What is Water Gas? Eq for formation?
A: Mixture of CO + H₂. Equation: C(s) + H₂O(g) → CO(g) + H₂(g).
6.5 Oxidation and Reduction (in terms of O/H)
Key Points:
  • Oxidation: Addition of Oxygen / Removal of Hydrogen.
  • Reduction: Removal of Oxygen / Addition of Hydrogen.
  • Oxidizing Agent: Causes oxidation (gets reduced). Supplies O / removes H.
  • Reducing Agent: Causes reduction (gets oxidized). Supplies H / removes O.
  • Redox Reaction: Oxidation & Reduction occur simultaneously. Example: CuO + H₂ → Cu + H₂O (CuO reduced, H₂ oxidized).

Critical Concept Check: Can oxidation happen without reduction?

A: No. They are complementary processes and always occur together in a redox reaction.
Q: In ZnO + C → Zn + CO, identify substance oxidized & reduced.
A: Oxidized: C (gains O). Reduced: ZnO (loses O).
Try Yourselves - Chapter 6

1. Test for H₂ gas?

2. Metal reacts with cold water?

3. Metal reacts with alkali?

4. Reactants in lab prep?

5. How is H₂ collected?

6. Main steps in Bosch process?

7. Define Oxidation (O/H).

8. Define Reduction (O/H).

Micro Tests - Chapter 6
Micro Test 6.1 (H₂ Position & Properties - 10 Marks)

Test 6.1

Time: 8 Min

Answer the following.

  1. 1. Give one similarity of H with Alkali Metals.[2]
  2. 2. Give one similarity of H with Halogens.[2]
  3. 3. What is the lightest element?[1]
  4. 4. What happens when H₂ burns in air?[2]
  5. 5. Is H₂ soluble in water?[1]
  6. 6. Complete: CuO + H₂ → ? + ?[2]
Micro Test 6.2 (H₂ Prep from Water/Acids - 10 Marks)

Test 6.2

Time: 10 Min

Write balanced equations for:

  1. 1. Potassium with cold water.[2]
  2. 2. Magnesium with hot water.[2]
  3. 3. Iron with steam (show reversibility).[2]
  4. 4. Zinc with dilute sulphuric acid.[2]
  5. 5. Aluminium with dilute hydrochloric acid.[2]
Micro Test 6.3 (Lab Prep & Bosch Process - 10 Marks)

Test 6.3

Time: 10 Min

Answer the following.

  1. 1. Reactants used in lab preparation of H₂?[1]
  2. 2. Equation for lab preparation using H₂SO₄.[1]
  3. 3. Method of collection in lab? Why?[2]
  4. 4. One precaution during lab prep.[1]
  5. 5. What is Water Gas?[1]
  6. 6. Write equation for Water-Gas Shift reaction.[2]
  7. 7. How is CO₂ removed in Bosch process?[1]
  8. 8. How is CO removed in Bosch process?[1]
Micro Test 6.4 (Oxidation & Reduction - 10 Marks)

Test 6.4

Time: 8 Min

Answer based on O/H definition.

  1. 1. Define Oxidation.[2]
  2. 2. Define Reduction.[2]
  3. 3. Define Oxidizing Agent.[2]
  4. 4. Define Reducing Agent.[2]
  5. 5. In C + O₂ → CO₂, identify substance oxidized & oxidizing agent.[2]
7. Study of Gas Laws
Focus on Boyle's Law, Charles' Law, the Gas Equation, Kelvin scale, and explanations based on molecular motion.
7.1 Behaviour of Gases & Molecular Motion
Key Points: Kinetic Molecular Theory (Simplified)
  • Gases = tiny particles in constant, random motion.
  • Large spaces between particles (negligible volume).
  • Negligible forces between particles (ideal gas).
  • Elastic collisions.
  • Average Kinetic Energy ∝ Absolute Temperature (K).
  • Pressure: Force from collisions on walls.
  • Temp/Vol/Pressure Effects: Explained by changes in particle speed & collision frequency/force.

Critical Concept Check: Why avoid heating aerosol cans?

A: Heating ↑Temp → ↑KE/speed of molecules → More frequent/forceful collisions. At constant volume, Pressure ↑ significantly (P ∝ T). Can may burst.
Q: Effect of decreasing volume on pressure (const T)? Explain.
A:
  • Effect: Pressure increases (Boyle's Law).
  • Explanation: Molecules collide with walls more frequently in smaller space → greater force per unit area → higher pressure.
7.2 Gas Laws
Boyle's Law
Key Points:
  • Relates Pressure (P) & Volume (V).
  • Condition: Temperature constant.
  • Statement: V ∝ 1/P (inversely proportional).
  • Formula: PV = constant OR P₁V₁ = P₂V₂.

Example: 500 cm³ gas at 700 mmHg. Vol at 1400 mmHg (const T)?
P₁=700, V₁=500, P₂=1400, V₂=?
700 × 500 = 1400 × V₂ ⇒ V₂ = 250 cm³.

Critical Concept Check: Bubbles rising in water expand. Which law?

A: Boyle's Law. Pressure decreases as bubble rises → Volume increases (at approx const T).
Q: What does 'k' represent in PV=k?
A: Depends on mass of gas and the constant temperature.
Charles's Law
Key Points:
  • Relates Volume (V) & Absolute Temperature (T).
  • Condition: Pressure constant.
  • Statement: V ∝ T(K) (directly proportional).
  • Formula: V/T(K) = constant OR V₁/T₁ = V₂/T₂ (T in Kelvin!).

Example: 10 L gas at 273 K. Vol at 546 K (const P)?
V₁=10, T₁=273, V₂=?, T₂=546.
10/273 = V₂/546 ⇒ V₂ = 20 L.

Critical Concept Check: Graph of V vs T(°C): through origin?

A: No. Straight line intercepts T-axis at -273°C (Absolute Zero). V ∝ T(K), not T(°C).
Q: State Charles's Law. Constant quantities?
A:
  • Statement: At const P, volume of fixed mass gas ∝ Absolute Temp (K).
  • Constant: Pressure, Mass.
7.3 Absolute Zero & Kelvin Scale
Key Points:
  • Absolute Zero: Lowest theoretical temp (0 K or -273°C approx.). Motion ceases theoretically.
  • Kelvin Scale (K): Starts at 0 K. K = °C + 273. Essential for gas laws.
  • Standard Temperature & Pressure (STP): 273 K (0°C) and 760 mmHg (1 atm).

Critical Concept Check: Why is absolute zero theoretical?

A: Real gases liquefy/solidify before 0 K. Quantum mechanics implies residual 'zero-point energy'.
Q: Convert 25°C and -10°C to Kelvin.
A: 25°C = 298 K; -10°C = 263 K.
7.4 Gas Equation (Combined Gas Law)
Key Points:
  • Relates P, V, T when all three change (fixed mass).
  • Combines Boyle's & Charles' Laws.
  • Formula: PV/T(K) = constant OR P₁V₁/T₁ = P₂V₂/T₂.
  • T must be in Kelvin. P, V units must be consistent.

STP Calculation Example: 800 cm³ gas at -23°C and 780 mmHg. Vol at STP (0°C, 760 mmHg)?
P₁=780, V₁=800, T₁=-23+273=250 K.
P₂=760, V₂=?, T₂=0+273=273 K.
V₂ = (P₁V₁T₂)/(P₂T₁) = (780 × 800 × 273) / (760 × 250) ≈ 896.3 cm³.

Critical Concept Check: When does Gas Eq simplify to Boyle's Law?

A: When Temperature is constant (T₁ = T₂). The T terms cancel, leaving P₁V₁ = P₂V₂.
Q: State STP values (Temp K, Pressure mmHg).
A: Temp = 273 K. Pressure = 760 mmHg.
Try Yourselves - Chapter 7

1. State Gas Equation mathematically.

2. Convert -40°C to K.

3. 5L gas at 27°C → ?L at -73°C (const P)?

4. 200mL gas at 273K, 760mmHg → ?vol at 546K, 380mmHg?

5. Unit for Volume in Gas Equation?

6. Explain Charles' Law (mol motion).

Micro Tests - Chapter 7
Micro Test 7.1 (Laws/Defs - 10 Marks)

Test 7.1

Time: 10 Min

Answer all questions.

  1. 1. Boyle's Law relates P & V at constant ______. [1]
  2. 2. Charles' Law relates V & T at constant ______. [1]
  3. 3. Absolute Zero in °C? [1]
  4. 4. Temp scale used in gas laws? [1]
  5. 5. Gas Eq formula? [2]
  6. 6. Standard Temp (K)? [1]
  7. 7. Standard Pressure (atm)? [1]
  8. 8. Pressure caused by particle ______. [1]
  9. 9. If P const, V doubles, Abs T ______. [1]
Micro Test 7.2 (Boyle/Charles Calc - 10 Marks)

Test 7.2

Time: 12 Min

Answer all questions.

  1. 1. 400mL gas at 2atm. Vol at 1atm (const T)? [3]
  2. 2. 3L gas at 100K. Vol at 300K (const P)? [3]
  3. 3. Vol 60cm³ at 1.5atm. Pressure if vol→30cm³ (const T)? [3]
  4. 4. Temp unit in Charles' Law? [1]
Micro Test 7.3 (Gas Eq Calc - 10 Marks)

Test 7.3

Time: 12 Min

Answer all questions.

  1. 1. Convert 127°C to K. [1]
  2. 2. Convert 380 mmHg to atm. [1]
  3. 3. 2L gas at STP. Vol at 273°C, 1atm? [3]
  4. 4. 600mL gas at 0°C, 800mmHg. Vol at STP? [3]
  5. 5. Gas Eq combines which laws? [2]
Micro Test 7.4 (Concepts/Units - 10 Marks)

Test 7.4

Time: 10 Min

Answer all questions.

  1. 1. Unit of temp in Gas Eq? [1]
  2. 2. Value std pressure in mmHg? [1]
  3. 3. Boyle's Law holds at constant ______. [1]
  4. 4. Charles' Law holds at constant ______. [1]
  5. 5. Explain gas pressure using molecular motion. [3]
  6. 6. Explain effect temp increase on gas pressure (const V) using molecular motion. [3]
8. Atmospheric Pollution
Understand sources, formation (equations!), impacts of acid rain, global warming (GHGs), and ozone depletion (ODS names).
8.1 Acid Rain
Key Points:
  • Definition: Rain pH < 5.6.
  • Causes: SOₓ & NOₓ emissions.
  • Sources: SOₓ (Fossil fuels - coal/oil), NOₓ (High temp combustion - engines, furnaces: N₂ + O₂ → 2NO).
  • Formation Eqs:
    • H₂SO₄: S+O₂→SO₂; 2SO₂+O₂→2SO₃; SO₃+H₂O→H₂SO₄
    • HNO₃: N₂+O₂→2NO; 2NO+O₂→2NO₂; 4NO₂+2H₂O+O₂→4HNO₃
  • Impacts: Damages buildings (marble CaCO₃), acidifies water/soil, corrodes metals.

Critical Concept Check: Why acid rain problem far from source?

A: SOₓ/NOₓ gases travel long distances via wind, react in atmosphere to form acids, fall as rain far away.
Q: Balanced eq: N₂ + O₂ in engine?
A: N₂(g) + O₂(g)
8.2 Global Warming
Key Points:
  • Greenhouse Effect: Natural warming by GHGs trapping IR radiation.
  • Global Warming: Enhanced effect due to ↑GHGs from human activity → ↑Avg Temp.
  • GHGs & Sources:
    • CO₂: Fossil fuels, deforestation (Primary driver).
    • CH₄: Agriculture, landfills, gas leaks.
    • N₂O: Fertilizers, industry.
    • H₂O Vapour: Natural, amplifies warming (feedback).
    • Oxides of Nitrogen.
  • Impacts: Climate change, ice melt, sea level rise, extreme weather.
  • Mitigation: Reduce fossil fuels, stop deforestation, sustainable practices.

Critical Concept Check: Explain water vapour 'positive feedback'.

A: ↑Temp → ↑Evaporation → ↑H₂O vapour (GHG) → More heat trapped → ↑Temp → More evaporation... (Cycle reinforces warming).
Q: Major human activity causing ↑CO₂ besides fossil fuels?
A: Deforestation (reduces CO₂ absorption, burning releases stored CO₂).
8.3 Ozone Depletion
Key Points:
  • Ozone (O₃) Layer: In Stratosphere.
  • Function: Absorbs harmful UV-B radiation.
  • Formation: O₂ + UV → 2O; O + O₂ → O₃.
  • Depletion: Thinning of layer by Ozone Depleting Substances (ODS).
  • ODS (Names reqd): Chlorofluorocarbons (CFCs), Halons, Carbon tetrachloride, Methyl chloroform. (Reactions not required).
  • Impact: ↑UV-B → Skin cancer, cataracts, ecosystem damage.

Critical Concept Check: Why CFCs damaging despite release near ground?

A: CFCs are stable/unreactive in lower atmosphere → diffuse to stratosphere → UV breaks them down → releases Cl atoms → catalytically destroy O₃.
Q: Radiation absorbed by ozone layer? Importance?
A: Absorbs UV-B radiation. Important because UV-B harms living organisms (DNA damage, cancer, cataracts).
Try Yourselves - Chapter 8

1. Eq NOx formation in engines?

2. Greenhouse gas from landfills?

3. Formula of ozone?

4. Impact acid rain on soil?

5. Is Ozone beneficial near ground?

6. Source of N₂O?

7. Write eq for O₃ formation from O₂ and O.

8. What does CFC stand for?

Micro Tests - Chapter 8
Micro Test 8.1 (Acid Rain - 10 Marks)

Test 8.1

Time: 10 Min

Answer all questions.

  1. 1. Two main acids in acid rain? [2]
  2. 2. Main gas pollutant from burning sulphur in fuel?[1]
  3. 3. Main gas pollutant from high temp combustion N₂/O₂?[1]
  4. 4. Write eq: SO₃ + water → ?[2]
  5. 5. Write full eq: Formation of HNO₃ from NO₂.[2]
  6. 6. One impact acid rain on aquatic life?[1]
  7. 7. One impact acid rain on marble buildings?[1]
Micro Test 8.2 (Global Warming - 10 Marks)

Test 8.2

Time: 10 Min

Answer all questions.

  1. 1. Define Greenhouse Effect.[2]
  2. 2. Name main human-contributed greenhouse gas?[1]
  3. 3. Name GHG from agriculture/landfills?[1]
  4. 4. Main source of increased atmospheric CO₂?[1]
  5. 5. State one consequence of global warming.[1]
  6. 6. Give two ways to reduce GHG emissions.[2]
  7. 7. Which natural GHG amplifies warming?[1]
  8. 8. Name GHG from fertilizers.[1]
Micro Test 8.3 (Ozone Layer - 10 Marks)

Test 8.3

Time: 10 Min

Answer all questions.

  1. 1. Where is the ozone layer primarily found?[1]
  2. 2. Write the equation: O + O₂ → ?[1]
  3. 3. What is the main function of the ozone layer?[2]
  4. 4. Name the main class of chemicals causing ozone depletion.[1]
  5. 5. Write the full name for CFCs.[1]
  6. 6. Name another ODS besides CFCs.[1]
  7. 7. State one harmful effect of ozone depletion on human health.[2]
  8. 8. Chemical formula for ozone?[1]
Micro Test 8.4 (Mixed Pollution Concepts - 10 Marks)

Test 8.4

Time: 10 Min

Answer all questions.

  1. 1. Gas from engine causing acid rain? Formula?[1]
  2. 2. Gas from burning coal causing acid rain? Formula?[1]
  3. 3. Main GHG driving current global warming?[1]
  4. 4. GHG released from rice paddies?[1]
  5. 5. What does ODS stand for?[1]
  6. 6. Which atmospheric layer contains the 'good' ozone?[1]
  7. 7. Write the equation for the formation of SO₂ from S.[1]
  8. 8. Name one way deforestation contributes to global warming.[1]
  9. 9. Is ozone (O₃) considered a pollutant in the troposphere (near ground)?[1]
  10. 10. Name one method to reduce acid rain formation.[1]
9. Internal Assessment (Practicals)
Focus on: Careful Observation (colour changes, gas evolution, precipitates, sounds), Logical Deduction, Correct Identification (gases/ions), Safe Handling. Understand the purpose and expected results of each experiment.
Quick Links: Gas ID Heat Actions Acid Actions Flame Test Hard/Soft Water Pollution Study Practice Micro Tests
9.1 Gas Identification Summary
Key Identification Tests:
GasFormulaTest & ObservationSmell/Colour
HydrogenH₂Burns with 'Pop' soundColourless, Odourless
OxygenO₂Relights glowing splintColourless, Odourless
Carbon DioxideCO₂Turns lime water milkyColourless, Odourless
ChlorineCl₂Turns damp blue litmus red, then bleachesGreenish-yellow, Pungent
Hydrogen ChlorideHClForms dense white fumes with NH₃ rodColourless, Pungent
Sulphur DioxideSO₂Turns acidified K₂Cr₂O₇ greenColourless, Burning Sulphur
Hydrogen SulphideH₂STurns lead acetate paper blackColourless, Rotten Eggs
AmmoniaNH₃Turns red litmus blue; dense white fumes with HCl rodColourless, Pungent
Water VapourH₂O(g)Turns anhydrous CuSO₄ blue / CoCl₂ paper pinkColourless, Odourless
Nitrogen DioxideNO₂Reddish-brown gas; turns KI/starch paper blue-black (via I₂) or FeSO₄ brownRed-brown, Pungent

Critical Concept Check: Why does CO₂ turn limewater milky, but excess CO₂ makes it clear again?

A: Initially, CO₂ reacts with Ca(OH)₂ (limewater) to form insoluble CaCO₃ (milky): Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O. With excess CO₂, the insoluble CaCO₃ reacts further to form soluble Calcium Bicarbonate: CaCO₃ + H₂O + CO₂(excess) → Ca(HCO₃)₂(aq).
Q: Which two gases form dense white fumes when mixed?
A: Ammonia (NH₃) and Hydrogen Chloride (HCl), forming solid Ammonium Chloride (NH₄Cl).
9.2 Exp 1: Action of Heat
Procedure & Observations:
  • Heat substance (~0.5g) in dry test tube (gently→strongly). Observe changes (colour, state), test any gas evolved, note residue colour (hot & cold).
  • CuCO₃(Green): → Black residue (CuO) + Gas turns lime milky (CO₂).
  • ZnCO₃(White): → Yellow(hot)/White(cold) residue (ZnO) + CO₂.
  • Washing Soda(Na₂CO₃·10H₂O): → White powder (anhydrous Na₂CO₃) + Colourless droplets (H₂O).
  • CuSO₄·5H₂O(Blue): → White powder (anhydrous CuSO₄) + H₂O.
  • Nitrates (Zn, Cu, Pb): → Metal Oxide residue + Red-brown gas (NO₂) + Gas relights splint (O₂). [Pb(NO₃)₂ decrepitates].
  • NH₄Cl(White) / Iodine(Grey): Sublimes → Solid deposit higher up cooler part of tube.
  • (NH₄)₂Cr₂O₇(Orange): → Green fluffy residue (Cr₂O₃) + Colourless gas + H₂O + Sparks ('volcano').

Critical Concept Check: Heating nitrates often produces NO₂ and O₂. Which common metal nitrate decomposes differently, producing only nitrite and oxygen?

A: Nitrates of very reactive metals like Sodium (NaNO₃) and Potassium (KNO₃) decompose to form the metal nitrite and oxygen only (e.g., 2NaNO₃ → 2NaNO₂ + O₂). Nitrates of less reactive metals (Zn, Cu, Pb) give oxide + NO₂ + O₂.
Q: What is sublimation? Give an example from the experiments.
A: Sublimation is the direct change of state from solid to gas without passing through the liquid phase. Example: Heating Ammonium Chloride (NH₄Cl) or Iodine (I₂).
9.3 Exp 2: Action of Dilute H₂SO₄
Procedure & Observations:
  • Add dilute H₂SO₄ to substance in test tube. Warm gently if no initial reaction. Test any gas evolved.
  • Metal (e.g., Zn): Effervescence → H₂ gas (burns with pop sound).
  • Carbonate (e.g., Na₂CO₃): Brisk effervescence → CO₂ gas (turns lime water milky).
  • Sulphide (e.g., ZnS): → H₂S gas (rotten egg smell, turns lead acetate paper black).
  • Sulphite (e.g., Na₂SO₃): → SO₂ gas (burning sulphur smell, turns acidified K₂Cr₂O₇ green).

Critical Concept Check: Why is dilute H₂SO₄ preferred over dilute HCl for testing sulphites?

A: Dilute HCl can sometimes be oxidized by the sulphite to chlorine gas, which can interfere with the test for SO₂. Dilute H₂SO₄ is non-oxidizing under these conditions and reliably produces only SO₂ from sulphites.
Q: A salt reacts with dilute acid to give a gas smelling of rotten eggs. Identify the anion.
A: Sulphide ion (S²⁻), producing H₂S gas.
9.4 Exp 3: Flame Test
Procedure & Observations:
  • Clean Platinum wire loop repeatedly (dip in conc. HCl, heat in non-luminous flame until no colour seen).
  • Make a paste of the salt with a few drops of conc. HCl.
  • Take paste on loop, introduce into non-luminous flame base. Observe colour.
  • Na⁺: Persistent Golden Yellow.
  • K⁺: Lilac (Pale Violet) - View through blue cobalt glass if Na⁺ present.
  • Ca²⁺: Brick Red.

Critical Concept Check: Why is conc. HCl used to make the paste?

A: To convert the salt (especially if it's less volatile like carbonate or oxide) into its more volatile chloride, which vaporizes easily in the flame, allowing the metal ions to enter the flame and impart their characteristic colour.
Q: How would you detect Potassium ions using flame test if Sodium ions are also present?
A: View the flame through a blue cobalt glass. This filters out the bright yellow Sodium flame, allowing the lilac Potassium flame to be seen.
9.5 Exp 4: Hard & Soft Water
Procedure & Observations:
  • Identification: Shake water sample with soap solution. Soft water → Good lather quickly. Hard water → Scum formed, poor/no lather.
  • Softening Temp Hard Water: Boil a sample of temporary hard water. Cool it. Test with soap again → Lather forms (hardness removed).
  • Softening using Washing Soda: Add Na₂CO₃ solution to hard water sample. Shake. Test with soap → Lather forms (hardness removed).
  • Detergent Advantage: Shake hard water with detergent solution → Lather forms readily (unlike soap).

Critical Concept Check: What is the 'scum' formed when soap is used with hard water?

A: Scum is the insoluble precipitate formed when the sodium/potassium salt of the fatty acid in soap reacts with the Ca²⁺ or Mg²⁺ ions present in hard water. Example: Sodium Stearate (soap) + Ca²⁺ → Calcium Stearate↓ (scum) + 2Na⁺.
Q: State one advantage and one disadvantage of hard water.
A: Advantage: Pleasant taste / Provides calcium for bones. Disadvantage: Wastes soap / Forms scale in kettles/pipes.
9.6 Exp 5: Water Pollution Study
Aim: Identify potential sources of water pollution in the locality and suggest preventive measures.
Sources to look for:
  • Domestic Sewage discharge.
  • Industrial Effluents (chemicals, heat).
  • Agricultural Runoff (fertilizers, pesticides).
  • Solid Waste Dumping near water bodies.
  • Religious/Cultural activities (immersion of idols, etc.).
Preventive Steps (Examples):
  • Proper sewage treatment before discharge.
  • Treatment of industrial effluents.
  • Judicious use of fertilizers/pesticides; promote organic farming.
  • Proper solid waste management, prevent dumping.
  • Awareness campaigns, designated areas for cultural activities.

Critical Concept Check: How does agricultural runoff cause water pollution (eutrophication)?

A: Runoff carries excess fertilizers (Nitrates, Phosphates) into water bodies. These nutrients cause rapid growth of algae (algal bloom). When algae die and decompose, bacteria consume large amounts of dissolved oxygen, depleting it for aquatic life (fish kill). This process is eutrophication.
Q: Name one heavy metal pollutant that might come from industrial waste.
A: Lead (Pb), Mercury (Hg), Cadmium (Cd), Arsenic (As), Chromium (Cr).
Try Yourselves - Chapter 9 (Practicals)

1. Test for O₂ gas?

2. Residue colour on heating CuCO₃?

3. Gas evolved when dil H₂SO₄ added to Na₂SO₃?

4. Flame colour for K⁺?

5. How remove temporary hardness?

6. What substance sublimes on heating?

7. Test for H₂S?

8. Main pollutants causing acid rain?

Micro Tests - Chapter 9 (Practicals)
Micro Test 9.1 (Gas ID - 10 Marks)

Test 9.1

Time: 10 Min

Identify gas based on test:

  1. 1.Relights glowing splint. [1]
  2. 2.Turns lime water milky. [1]
  3. 3.Burns with pop sound. [1]
  4. 4.Turns lead acetate paper black. [1]
  5. 5.Reddish-brown coloured gas. [1]
  6. 6.Turns acidified K₂Cr₂O₇ green. [1]
  7. 7.Turns moist red litmus blue. [1]
  8. 8.Greenish-yellow gas that bleaches litmus. [1]
  9. 9.Forms dense white fumes with ammonia rod. [1]
  10. 10.Turns anhydrous copper sulphate blue. [1]
Micro Test 9.2 (Heat/Acid Rxns Obs - 10 Marks)

Test 9.2

Time: 10 Min

State key observation(s).

  1. 1.Heating Zinc Carbonate. [1]
  2. 2.Heating Copper(II) Sulphate crystals. [2]
  3. 3.Heating Ammonium Chloride. [1]
  4. 4.Heating Lead Nitrate. [2]
  5. 5.Dil H₂SO₄ + Sodium Sulphite. [2]
  6. 6.Dil H₂SO₄ + Zinc Sulphide. [2]
Micro Test 9.3 (Flame/Water Tests - 10 Marks)

Test 9.3

Time: 10 Min

Answer all questions.

  1. 1.Flame colour Ca²⁺? [1]
  2. 2.Flame colour Na⁺? [1]
  3. 3.Flame colour K⁺? [1]
  4. 4.How distinguish hard/soft water using soap? [2]
  5. 5.Name chemical causing temp hardness. [1]
  6. 6.Name chemical causing perm hardness. [1]
  7. 7.Method removing temp hardness only? [1]
  8. 8.Method removing both hardness types? [1]
  9. 9.Detergent advantage in hard water? [1]
Micro Test 9.4 (Conceptual Practical - 10 Marks)

Test 9.4

Time: 10 Min

Answer all questions.

  1. 1. White substance + dil acid → brisk effervescence, gas turns lime milky. Identify anion.[2]
  2. 2. Blue crystals heat → white powder + colourless liquid. Test for liquid?[2]
  3. 3. Substance gives brick red flame. Cation?[1]
  4. 4. Substance gives lilac flame. Cation?[1]
  5. 5. What is the green fluffy residue from heating (NH₄)₂Cr₂O₇?[1]
  6. 6. Why add conc HCl for flame test?[1]
  7. 7. Name one source of thermal pollution in water.[1]
  8. 8. Test for Ammonia gas?[1]