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ICSEClass 10Science★ ICSE Class 10 Science (Chemistry) · ~25 marks · Board: ICSE

Chemistry — Periodic Table, Bonding, Acids, Electrolysis, Metallurgy & Organic

ICSE Class 10 Chemistry: The PERIODIC TABLE (Mendeleev → Modern). CHEMICAL BONDING (ionic, covalent, coordinate). ACIDS, BASES, SALTS and analytical chemistry. MOLE CONCEPT and STOICHIOMETRY. ELECTROLYSIS. METALLURGY. Study of HCl, NH₃, HNO₃, H₂SO₄. And INTRODUCTION TO ORGANIC CHEMISTRY. ICSE Class 10 Science.

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By the end of this chapter you'll be able to…

  • 1Explain periodic trends (atomic size, ionization energy, metallic character) across periods and down groups using atomic structure
  • 2Distinguish ionic, covalent, and coordinate bonds; draw dot-cross diagrams for common molecules
  • 3Explain acid-base theories, pH, and analytical chemistry tests for identifying anions and cations
  • 4Apply the mole concept and stoichiometry to calculate masses, volumes, and concentrations in reactions
  • 5Describe electrolysis — predict electrode products for molten and aqueous electrolytes; explain preferential discharge
  • 6Outline the extraction of metals by reduction (carbon reduction, electrolytic reduction) and explain refining
  • 7Write IUPAC names for hydrocarbons (alkanes, alkenes, alkynes); identify and name functional groups; describe substitution and addition reactions
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Why this chapter matters
ICSE Chemistry is systematic and highly rewarding: the syllabus is defined, the question types repeat year to year, and the marks are very accessible. The Periodic Table, Chemical Bonding, Acids/Bases, Electrolysis, and Organic Chemistry together cover the majority of the ICSE Chemistry paper. Electrolysis alone is 8–10 marks every year and is learned by understanding the logic (cations go to cathode, anions to anode). Organic Chemistry (hydrocarbons + functional groups) is the modern half of chemistry and tested as 2–3 mark recall questions. Students who master this file reliably score 20+ marks in Chemistry.

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A 5-minute refresher here will save you 30 minutes of confusion below.

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Chemistry — Periodic Table, Bonding, Acids, Electrolysis, Metallurgy & Organic

1. Periodic Table

Mendeleev's Table

Arranged by increasing ATOMIC MASS. 'Left gaps for undiscovered elements — predicted their properties. This was his GENIUS.'

Modern Periodic Law (Moseley)

'Properties are a periodic function of ATOMIC NUMBER.' Groups (vertical — 18). Periods (horizontal — 7).

  • Atomic size: ↓ across period (→). ↑ down group (↓). 'More protons pull electrons closer.'
  • Metallic character: ↓ across period. ↑ down group.

2. Chemical Bonding

Bond TypeHowExample
Ionic (Electrovalent)TRANSFER of electrons. Metal + Non-metal.NaCl. MgO.
CovalentSHARING of electrons. Non-metal + Non-metal.H₂. H₂O. CH₄.
Coordinate (Dative)BOTH shared electrons from SAME atom.NH₄⁺. H₃O⁺.

Properties of Ionic vs. Covalent Compounds

PropertyIonicCovalent
Melting/Boiling pointHIGHLOW
Electrical conductivityConduct when MOLTEN/DISSOLVEDDo NOT conduct
SolubilitySoluble in WATERSoluble in ORGANIC solvents

3. Acids, Bases and Salts

Arrhenius Theory

  • ACID: Produces H⁺ ions in water. HCl, H₂SO₄.
  • BASE: Produces OH⁻ ions in water. NaOH, KOH.

Properties

  • Acids: Sour. Turn BLUE litmus RED. React with metals → H₂ gas. React with carbonates → CO₂.
  • Bases: Bitter. Soapy feel. Turn RED litmus BLUE.

pH Scale: 0 (strong acid) → 7 (neutral) → 14 (strong base).

Types of Salts

Normal. Acid (contains replaceable H). Basic (contains replaceable OH). Double. Mixed. Complex.

4. Analytical Chemistry

Tests for Cations (Using NaOH and NH₄OH)

Metal IonWith NaOHWith NH₄OH (excess)
Cu²⁺Blue pptDeep BLUE solution
Fe²⁺Dirty green pptInsoluble
Fe³⁺Reddish-brown pptInsoluble
Zn²⁺White gelatinous pptSOLUBLE (colourless)
Pb²⁺White pptInsoluble

Tests for Anions

  • Chloride: White ppt with AgNO₃ (soluble in NH₄OH). Bromide: Cream ppt. Iodide: Yellow ppt.
  • Sulphate: White ppt with BaCl₂ (insoluble in HCl).
  • Carbonate: Effervescence with dil. HCl. Gas turns limewater milky.

5. Mole Concept and Stoichiometry

Key Relationships

  • 1 mole = 6.022 × 10²³ particles (Avogadro's Number).
  • Moles = Mass / Molar mass. Moles = Volume (at STP) / 22.4 L.

Gay-Lussac's Law of Combining Volumes

Gases react in SIMPLE WHOLE-NUMBER RATIOS by volume.

Percentage Composition and Empirical Formula

6. Electrolysis

Key Terms

  • Electrolyte: solution/molten compound that CONDUCTS electricity.
  • Cathode (—): Attracts CATIONS (+). REDUCTION.
  • Anode (+): Attracts ANIONS (—). OXIDATION.

Electrolysis of Key Compounds

CompoundAt Cathode (—)At Anode (+)
Molten NaClNa (metal)Cl₂ (gas)
Aqueous NaClH₂ (gas)Cl₂ (gas)
Aqueous CuSO₄ (inert electrodes)Cu (deposited)O₂ (gas)

Applications

Electroplating (chromium, silver, gold). Refining of metals (copper).

7. Metallurgy

Steps

  1. Concentration of ore. 2. Roasting/Calcination (conversion to oxide). 3. REDUCTION to metal. 4. Refining.

Extraction of Aluminium (Hall-Héroult Process)

Electrolytic reduction of Al₂O₃ dissolved in molten CRYOLITE. Anode: Carbon (consumed → CO₂). Cathode: Aluminium metal.

Alloys — Mixture of metals for improved properties

Brass (Cu+Zn). Bronze (Cu+Sn). Stainless steel (Fe+Cr+Ni). Solder (Pb+Sn).

8. Study of Compounds

Hydrogen Chloride (HCl gas)

Colourless, pungent. Highly soluble in water → HYDROCHLORIC ACID. 'Fountain experiment.' Test: White FUMES with NH₃ → NH₄Cl.

Ammonia (NH₃)

Colourless, pungent. LIGHTER than air. Highly soluble → weak ALKALINE solution. Test: Turns red litmus BLUE. White fumes with HCl. Haber Process: N₂ + 3H₂ ⇌ 2NH₃ (Fe catalyst, 450°C, 200 atm).

Nitric Acid (HNO₃)

Strong OXIDISING agent. Prepared by Ostwald's process. 'Brown Ring Test' for nitrate.

Sulphuric Acid (H₂SO₄)

'King of Chemicals.' Contact Process: 2SO₂ + O₂ ⇌ 2SO₃ (V₂O₅ catalyst). SO₃ + H₂SO₄ → Oleum. Dilution → H₂SO₄. Non-volatile. Dehydrating agent (chars sugar → carbon).

9. Organic Chemistry — Introduction

Unique Nature of Carbon

CATENATION (ability to form chains). TETRAVALENCY (4 bonds).

Hydrocarbons

TypeFormulaBondExample
AlkaneCₙH₂ₙ₊₂SINGLE (C—C)CH₄ (methane)
AlkeneCₙH₂ₙDOUBLE (C=C)C₂H₄ (ethene)
AlkyneCₙH₂ₙ₋₂TRIPLE (C≡C)C₂H₂ (ethyne/acetylene)

Functional Groups

GroupFormulaCompound Type
—OHAlcoholEthanol (C₂H₅OH)
—CHOAldehydeMethanal (HCHO)
—COOHCarboxylic AcidEthanoic acid (CH₃COOH)

Homologous Series

Same general formula. Same functional group. Differ by —CH₂—. Gradual change in physical properties.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Periodic Table Trends
ATOMIC SIZE: Decreases across a period (→) — more protons pull electrons closer. Increases down a group (↓) — more shells added. IONIZATION ENERGY: Increases across period (harder to remove electrons from larger nuclear charge). Decreases down group. ELECTRON AFFINITY: Generally increases across period. METALLIC CHARACTER: Decreases across period (metals on left, non-metals on right). Increases down group (easier to lose electrons). ELECTRONEGATIVITY: Increases across period, decreases down group. Most electronegative: Fluorine.
PERIOD 3 (Na to Cl) is the MOST TESTED period in ICSE: Na (metal, loses 1e⁻) → Mg (metal, 2e⁻) → Al (metal, 3e⁻) → Si (metalloid) → P (non-metal) → S (non-metal) → Cl (non-metal, gains 1e⁻). Properties change smoothly. Questions: 'Explain why Cl has higher electron affinity than Na' → Cl has more protons, smaller size, stronger attraction for electrons.
Mole Concept
1 MOLE = 6.022 × 10²³ particles (Avogadro's number). MOLAR MASS: Mass of 1 mole in grams = molecular mass in g/mol. MOLES = Given mass / Molar mass. MOLES = Number of particles / 6.022 × 10²³. VOLUME (gases at STP): 1 mole of any gas = 22.4 L at STP (0°C, 1 atm). Moles of gas = Volume at STP / 22.4. STOICHIOMETRY: Use balanced equation mole ratios to relate moles of reactants and products.
STOICHIOMETRY STEPS: (1) Write and balance the equation. (2) Write the mole ratio from the equation. (3) Find moles of given substance. (4) Use ratio to find moles of required substance. (5) Convert moles to mass/volume as needed. Example: 2H₂ + O₂ → 2H₂O. If 4 g H₂ reacts, moles H₂ = 4/2 = 2. Moles H₂O = 2 (1:1 ratio). Mass H₂O = 2 × 18 = 36 g.
Electrolysis
CATHODE (−): REDUCTION occurs. Cations (positive ions) move toward cathode and GAIN electrons. ANODE (+): OXIDATION occurs. Anions (negative ions) move toward anode and LOSE electrons. PREFERENTIAL DISCHARGE: If multiple ions present, SELECTIVE discharge occurs based on: (1) Position in electrochemical series (less active metals discharge preferentially at cathode — copper before hydrogen before sodium). (2) Concentration of ions (high concentration → preferential discharge even against electro-series). ELECTROLYSIS OF CuSO₄ (aq, copper electrodes): Cathode: Cu²⁺ + 2e⁻ → Cu (copper deposited). Anode: Cu → Cu²⁺ + 2e⁻ (copper dissolves). ELECTROPLATING principle: object to be plated = cathode, plating metal = anode, salt solution of metal = electrolyte.
ICSE TESTS: Electrolysis of (1) molten NaCl: cathode Na, anode Cl₂. (2) Aqueous NaCl: cathode H₂ (H⁺ discharged preferentially over Na⁺), anode Cl₂ (Cl⁻ discharged preferentially over OH⁻ due to HIGH concentration). (3) CuSO₄ with carbon electrodes: cathode Cu, anode O₂. (4) CuSO₄ with copper electrodes: cathode Cu deposited, anode Cu dissolves. Always state what goes to CATHODE, what to ANODE, with equations.
Organic Chemistry
ALKANES: CₙH₂ₙ₊₂. Saturated. Single bonds. ALKENES: CₙH₂ₙ. One double bond. ALKYNES: CₙH₂ₙ₋₂. One triple bond. KEY FUNCTIONAL GROUPS: Alcohol (−OH), Aldehyde (−CHO), Ketone (−CO−), Carboxylic Acid (−COOH), Amine (−NH₂). REACTIONS: Alkanes → SUBSTITUTION with halogen (UV light). Alkenes → ADDITION of H₂ (hydrogenation), HX, or X₂ (halogenation). Alcohols → oxidised to aldehydes/ketones/acids. IUPAC NAMES: Count the longest carbon chain (meth-1, eth-2, prop-3, but-4, pent-5, hex-6). Identify the highest priority functional group. Number from the end nearest the functional group.
ICSE ORGANIC TESTS: Alkene vs alkane: Alkene DECOLOURISES bromine water (addition reaction). Alkane does NOT. Aldehyde vs ketone: Aldehyde gives silver mirror with Tollens' reagent. Ketone does not. Glucose (C₆H₁₂O₆) is an aldehyde sugar — it gives silver mirror test. Fructose is a ketone sugar. Carboxylic acid: turns blue litmus red, reacts with Na₂CO₃ to give CO₂ (fizzing).
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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT
✗ Drawing the wrong ion at the cathode in electrolysis questions
✓ CATHODE attracts CATIONS (positively charged ions). ANODE attracts ANIONS. Memory: CATHode = CAThions. ANOde = ANions. In aqueous solutions, apply PREFERENTIAL DISCHARGE: At cathode, metal ions (Cu²⁺, Ag⁺) are discharged before H⁺ (except for very reactive metals like Na⁺, K⁺, Ca²⁺ — in their case H₂ is discharged instead). At anode: Cl⁻ (if concentrated) before OH⁻; otherwise O₂ is produced.
WATCH OUT
✗ Confusing molecular formula with structural formula when naming organic compounds
✓ MOLECULAR FORMULA gives the total count of atoms (C₃H₆O could be an aldehyde OR a ketone). STRUCTURAL FORMULA shows HOW atoms are connected. For IUPAC naming: (1) Find the longest carbon chain. (2) Identify the functional group and its position. (3) Number from the end nearest the functional group. Example: CH₃−CH(OH)−CH₃ → propan-2-ol (OH on carbon 2). CH₃−CH₂−OH → ethanol (OH on carbon 1 = end, so just 'ethanol').
WATCH OUT
✗ Applying periodic trends in the wrong direction
✓ TWO DIRECTIONS to remember: LEFT TO RIGHT across a period: atomic size decreases, ionization energy increases, metallic character decreases, electronegativity increases (more non-metallic character). TOP TO BOTTOM down a group: atomic size increases, ionization energy decreases, metallic character increases (more reactive metals), electronegativity decreases. 'Across: more nuclear charge, smaller, harder to ionise.' 'Down: more shells, bigger, easier to ionise.'

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· mole-concept
Calculate the number of molecules in 44 g of CO₂. (Molecular mass of CO₂ = 44 g/mol, Avogadro's number = 6 × 10²³)
▶ Show solution
Moles of CO₂ = given mass / molar mass = 44 / 44 = 1 mole. Number of molecules = 1 × 6 × 10²³ = 6 × 10²³ molecules. Also: in 1 mole CO₂, there are 1 mole C atoms (= 6 × 10²³ C atoms) and 2 moles O atoms (= 1.2 × 10²⁴ O atoms).
Q2MEDIUM· electrolysis-products
Acidified water (dilute H₂SO₄ solution) is electrolysed using platinum electrodes. Identify the products at each electrode. Write the ionic equations. Explain why the volume of gas at the cathode is double that at the anode.
▶ Show solution
CATHODE (−): H⁺ ions are reduced. 2H⁺ + 2e⁻ → H₂ (hydrogen gas produced). ANODE (+): OH⁻ ions are oxidised. 4OH⁻ → 2H₂O + O₂ + 4e⁻ (oxygen gas produced). OVERALL: 2H₂O → 2H₂ + O₂ (electrolysis of water). VOLUME RATIO: From the equation, H₂ : O₂ = 2 : 1. So volume of H₂ at cathode is TWICE the volume of O₂ at anode. (Equal number of moles at same T and P would have equal volume by Avogadro's law; here the mole ratio from the equation is 2:1.)
Q3HARD· organic-reactions-chain
Starting from ethane (C₂H₆), show how you would obtain (a) bromoethane, (b) ethene, (c) ethanol, (d) ethanoic acid (acetic acid). State the type of each reaction.
▶ Show solution
(a) Ethane → Bromoethane: CH₃CH₃ + Br₂ →(UV light)→ CH₃CH₂Br + HBr. Type: SUBSTITUTION (free radical halogenation). (b) Bromoethane → Ethene: CH₃CH₂Br + KOH(alcoholic) → CH₂=CH₂ + KBr + H₂O. Type: ELIMINATION (dehydrohalogenation). Alternatively: Ethane can be cracked/dehydrogenated. (c) Ethene → Ethanol: CH₂=CH₂ + H₂O →(H₃PO₄ catalyst, 300°C, 60 atm)→ CH₃CH₂OH. Type: ADDITION (hydration). (d) Ethanol → Ethanoic Acid: CH₃CH₂OH →(acidified K₂Cr₂O₇ or KMnO₄)→ CH₃COOH. Type: OXIDATION.

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