ICSE Class 10 Chemistry: Do-or-Die Chapters & Last-Minute Revision Notes (2027)
Tushar Parik
Author
Chemistry Doesn't Have to Be Scary.
ICSE Chemistry is one of those subjects where a focused 2-week revision can genuinely change your score by 15-20 marks. Why? Because the syllabus is predictable, reactions repeat across years, and nearly 65% of the paper comes from just 4-5 chapters. This guide identifies the exact do-or-die chapters, lists every reaction you must memorise, gives you balancing tricks that save time, and covers the lab-based questions examiners love. Whether your exam is next week or next month, start here.
In This Article
Exam Pattern & Marking Scheme
Before you revise a single reaction, understand how the paper is structured. Knowing the exam pattern lets you allocate time intelligently and target the sections that carry the most marks.
- Total Marks: 80 (Theory) + 20 (Internal Assessment) = 100
- Section A (40 marks): Compulsory short-answer questions covering the entire syllabus. You cannot skip any chapter here.
- Section B (40 marks): Answer any 4 out of 6 structured/long-answer questions. This is where chapter selection matters most.
- Duration: 2 hours for the theory paper
- Key Insight: Section B gives you the power of choice. If you master 4-5 chapters thoroughly, you can strategically pick the easiest questions and score 35-40 out of 40 in this section.
Chapter-Wise Weightage Table
CISCE does not officially publish chapter-wise weightage, but analysis of previous year papers (2018-2025) reveals a consistent pattern. Use this table to prioritise your revision — chapters marked with a star are your do-or-die chapters.
| Chapter | Approx. Marks | Priority | Key Focus Areas |
|---|---|---|---|
| Study of Compounds (HCl, HNO₃, H₂SO₄) | 18-20 | Do-or-Die | Lab preparation, properties, reactions, tests |
| Organic Chemistry | 10-12 | Do-or-Die | Homologous series, functional groups, IUPAC naming, reactions of ethanol & ethanoic acid |
| Electrolysis | 8-10 | Do-or-Die | Electrode reactions, electroplating, selective discharge, electrolysis of acidulated water |
| Mole Concept & Stoichiometry | 8-10 | Do-or-Die | Mole calculations, Gay-Lussac's law, Avogadro's law, empirical/molecular formula |
| Periodic Table & Periodicity | 6-8 | High | Periodic trends, atomic radius, ionisation energy, electron affinity, metallic character |
| Chemical Bonding | 6-8 | High | Electrovalent vs covalent, electron dot structures, coordinate bonding, properties |
| Acids, Bases & Salts | 5-6 | High | pH scale, indicators, neutralisation, salt types, definitions |
| Metallurgy | 5-6 | Medium | Extraction of aluminium & iron, alloys, ore terminology |
| Analytical Chemistry | 4-5 | Medium | Action of NaOH & NH₄OH on salt solutions, flame tests, gas identification |
Bottom line: Study of Compounds, Organic Chemistry, Electrolysis, and Mole Concept together account for roughly 50-52 marks out of 80. Master these four and you have already secured more than half the paper.
Do-or-Die Chapters: Deep Dive
1. Study of Compounds — HCl, HNO₃, H₂SO₄ (18-20 Marks)
This is the single highest-scoring chapter in the entire Chemistry paper. It appears in both Section A and Section B every single year. You simply cannot afford to skip it.
What to Focus On
- Hydrogen Chloride (HCl): Lab preparation from NaCl + conc. H₂SO₄, drying agent (conc. H₂SO₄), collection by upward displacement, fountain experiment, reaction with ammonia (white fumes of NH₄Cl)
- Nitric Acid (HNO₃): Lab preparation from KNO₃ + conc. H₂SO₄ below 200°C, oxidising properties (reaction with Cu, C, S), brown ring test for nitrate ion, aqua regia composition
- Sulphuric Acid (H₂SO₄): Contact process (V₂O₅ catalyst, 450°C), role as dehydrating agent, dilution procedure (add acid to water, never water to acid), reactions as dibasic acid
- Exam Tip: For every compound, learn the preparation equation, 3-4 chemical properties, and the confirmatory test. This pattern covers 90% of questions asked.
2. Organic Chemistry (10-12 Marks)
Organic Chemistry is the second highest-scoring topic and is a favourite for long-answer questions in Section B. Students who prepare this chapter well can almost guarantee themselves a full-marks question in Section B.
What to Focus On
- Homologous Series: Definition, characteristics, general formulae for alkanes (CₙH₂ₙ₊₂), alkenes (CₙH₂ₙ), alkynes (CₙH₂ₙ₋₂)
- IUPAC Naming: Practice naming and drawing structural formulae for compounds with up to 5 carbon atoms. Pay attention to branched-chain naming.
- Functional Groups: Hydroxyl (-OH), carboxyl (-COOH), aldehyde (-CHO), ketone (-CO-). Know the compound type each group defines.
- Reactions of Ethanol: Combustion, oxidation with acidified K₂Cr₂O₇/KMnO₄, dehydration with conc. H₂SO₄ at 170°C to form ethene, esterification with ethanoic acid
- Reactions of Ethanoic Acid: Reaction with NaOH (neutralisation), Na₂CO₃ (effervescence of CO₂), NaHCO₃, esterification, reaction with alcohols
- Addition vs Substitution: Unsaturated hydrocarbons undergo addition; saturated undergo substitution. Be ready to give one example of each.
3. Electrolysis (8-10 Marks)
Electrolysis questions are highly scoring because they follow a fixed pattern: identify the electrolyte, write electrode reactions, and state the product. Once you understand the selective discharge theory, this chapter becomes a mark-scoring machine.
What to Focus On
- Key Definitions: Electrolyte vs non-electrolyte, strong vs weak electrolyte, anode, cathode, anion, cation
- Selective Discharge: When multiple ions are present, the ion lower in the electrochemical series is discharged first at the cathode, and the ion higher in the activity series is discharged first at the anode
- Must-Know Electrolysis Examples: Acidulated water (dilute H₂SO₄), CuSO₄ solution with copper/platinum electrodes, molten PbBr₂, NaCl solution
- Applications: Electroplating (object at cathode, plating metal at anode, salt of plating metal as electrolyte), electrorefining of copper
- Exam Tip: Always write electrode reactions with proper charge balancing. Specify which gas is evolved at which electrode and include any colour changes observed.
4. Mole Concept & Stoichiometry (8-10 Marks)
This chapter is numerical-heavy and appears without fail in both sections. The good news: once you understand the three relationships (mole-mass, mole-volume, mole-particles), every problem becomes a formula application.
Must-Know Formulae
- Number of moles = Given mass / Molar mass
- Number of particles = Number of moles × 6.022 × 10²³ (Avogadro's number)
- Volume at STP = Number of moles × 22.4 L (for gases)
- Vapour density = Molar mass / 2
- Empirical formula: Divide each element's mole ratio by the smallest to get the simplest whole-number ratio
- Molecular formula = n × Empirical formula, where n = Molecular mass / Empirical formula mass
- Gay-Lussac's Law: Gases react in volumes that bear a simple whole-number ratio to each other and to the volume of gaseous products (at same T and P)
- Avogadro's Law: Equal volumes of all gases at the same temperature and pressure contain the same number of molecules
5. Periodic Table & Chemical Bonding (12-16 Marks Combined)
These two chapters are closely linked and frequently appear together. They form the conceptual foundation for the rest of the syllabus, so understanding them well also helps with other chapters.
Periodic Table: Key Trends to Memorise
- Across a period (left to right): Atomic radius decreases, ionisation energy increases, electron affinity increases (generally), electronegativity increases, metallic character decreases
- Down a group (top to bottom): Atomic radius increases, ionisation energy decreases, electronegativity decreases, metallic character increases
- Common Question Types: Arrange elements in order of a given property, identify the element with highest/lowest value, explain why a trend occurs using atomic structure
Chemical Bonding: What Examiners Love
- Electrovalent (Ionic) Bonding: Transfer of electrons, formation of ions, high melting point, conducts electricity in molten/dissolved state. Example: NaCl, MgO, CaF₂
- Covalent Bonding: Sharing of electrons, low melting point, does not conduct electricity. Example: H₂O, CH₄, NH₃, CO₂
- Coordinate (Dative) Bonding: One atom donates both shared electrons. Example: NH₄⁺ ion, H₃O⁺ ion
- Electron Dot Structures: Practice drawing them for NaCl, MgCl₂, CaCl₂, H₂O, NH₃, CH₄, C₂H₄, CCl₄
- Comparison Questions: Be ready to compare properties of electrovalent vs covalent compounds in a tabular format (5-6 differences)
Key Reactions You Must Memorise
This is the single most important section of this article. Memorise every reaction below — they cover 80% of the equations asked in board exams over the last 8 years.
Study of Compounds
Hydrogen Chloride
- Lab Preparation: NaCl + H₂SO₄ (conc.) → NaHSO₄ + HCl↑ (below 200°C)
- Above 200°C: NaCl + NaHSO₄ → Na₂SO₄ + HCl↑
- With Ammonia: NH₃ + HCl → NH₄Cl (white fumes)
- With Iron: Fe + 2HCl → FeCl₂ + H₂↑
Nitric Acid
- Lab Preparation: KNO₃ + H₂SO₄ (conc.) → KHSO₄ + HNO₃↑ (below 200°C)
- With Copper (conc.): Cu + 4HNO₃ (conc.) → Cu(NO₃)₂ + 2H₂O + 2NO₂↑ (brown gas)
- With Copper (dilute): 3Cu + 8HNO₃ (dilute) → 3Cu(NO₃)₂ + 4H₂O + 2NO↑ (colourless gas, turns brown in air)
- With Carbon: C + 4HNO₃ (conc.) → CO₂↑ + 4NO₂↑ + 2H₂O
- With Sulphur: S + 6HNO₃ (conc.) → H₂SO₄ + 6NO₂↑ + 2H₂O
Sulphuric Acid
- Contact Process Step 1: S + O₂ → SO₂
- Contact Process Step 2: 2SO₂ + O₂ ⇌ 2SO₃ (V₂O₅ catalyst, 450°C)
- Contact Process Step 3: SO₃ + H₂SO₄ → H₂S₂O₇ (oleum)
- Oleum Dilution: H₂S₂O₇ + H₂O → 2H₂SO₄
- Dehydrating Action: C₂H₁₂O₁₁ (sugar) ⟶ H₂SO₄ 12C + 11H₂O
Electrolysis Reactions
- Acidulated Water — Cathode: 4H⁺ + 4e⁻ → 2H₂↑
- Acidulated Water — Anode: 4OH⁻ - 4e⁻ → 2H₂O + O₂↑
- CuSO₄ with Pt electrodes — Cathode: Cu²⁺ + 2e⁻ → Cu (copper deposited)
- CuSO₄ with Pt electrodes — Anode: 4OH⁻ - 4e⁻ → 2H₂O + O₂↑
- CuSO₄ with Cu electrodes — Anode: Cu - 2e⁻ → Cu²⁺ (anode dissolves)
- Molten PbBr₂ — Cathode: Pb²⁺ + 2e⁻ → Pb
- Molten PbBr₂ — Anode: 2Br⁻ - 2e⁻ → Br₂
Metallurgy Reactions
- Calcination: ZnCO₃ → ZnO + CO₂↑
- Roasting: 2ZnS + 3O₂ → 2ZnO + 2SO₂↑
- Reduction with Carbon: ZnO + C → Zn + CO↑
- Thermite Reaction: Fe₂O₃ + 2Al → Al₂O₃ + 2Fe (used for welding railway tracks)
- Aluminium Extraction (Hall-Héroult): 2Al₂O₃ → 4Al + 3O₂ (electrolysis, cryolite as flux)
Balancing Equations: Tricks That Save Time
Balancing chemical equations is a skill that appears in virtually every section of the paper. Here are five practical tricks that make it faster and more reliable.
1. Balance Metals First
Always start by balancing metal atoms, then non-metals, and finally hydrogen and oxygen last. Oxygen is usually the easiest to adjust at the end because it appears in multiple compounds.
2. Treat Polyatomic Ions as Units
If a polyatomic ion (SO₄²⁻, NO₃⁻, CO₃²⁻) appears unchanged on both sides, balance it as a single unit instead of balancing individual atoms. This dramatically reduces complexity.
3. Use Even Numbers for Oxygen
Since O₂ has 2 oxygen atoms, if you have an odd number of oxygen atoms on one side, double all coefficients first. Then balance oxygen. This avoids fractional coefficients entirely.
4. Verify Your Count
After balancing, count every atom on both sides. Write the count below the equation if needed. A single miscounted atom means zero marks for the equation, so this 10-second check is worth it.
5. Memorise Standard Equations
For board exams, most equations are standard reactions from your textbook. Rather than balancing from scratch under pressure, memorise the 25-30 key equations listed in this article. Write them daily until they become automatic.
Lab-Based & Practical Questions
Lab-based questions are guaranteed marks if you prepare them properly. They follow a fixed format: identify the gas/compound, write the preparation method, give the equation, and describe the confirmatory test. Here are the most frequently tested topics.
| Gas / Compound | Lab Preparation | Confirmatory Test |
|---|---|---|
| HCl gas | NaCl + conc. H₂SO₄; collect by upward displacement | White fumes with NH₃; turns moist blue litmus red |
| HNO₃ | KNO₃ + conc. H₂SO₄ below 200°C in glass retort | Brown ring test; turns copper turnings to blue solution with brown fumes |
| H₂ gas | Zn + dil. H₂SO₄; collect by downward displacement of water | Burns with a pop sound; colourless, odourless |
| CO₂ gas | CaCO₃ + dil. HCl | Turns lime water milky; milkiness disappears with excess CO₂ |
| NH₃ gas | NH₄Cl + Ca(OH)₂; collect by downward displacement of air | Turns moist red litmus blue; white fumes with HCl |
| Cl₂ gas | MnO₂ + conc. HCl | Turns moist starch-iodide paper blue; pungent greenish-yellow gas |
| SO₂ gas | Na₂SO₃ + dil. H₂SO₄ | Turns acidified K₂Cr₂O₇ from orange to green; suffocating smell |
Analytical Chemistry: Quick Identification Tests
- NaOH test: Add NaOH solution to the salt solution. A blue precipitate indicates Cu²⁺, green indicates Fe²⁺ (turns brown on standing), rusty brown indicates Fe³⁺, and white gelatinous precipitate soluble in excess NaOH indicates Al³⁺ or Zn²⁺.
- NH₄OH test: Cu²⁺ gives a light blue precipitate that dissolves in excess to form a deep blue solution. Fe²⁺ and Fe³⁺ precipitates are insoluble in excess.
- Flame tests: Na gives golden yellow, K gives lilac/violet, Ca gives brick red, Cu gives blue-green.
Last-Minute Revision Checklist
Use this checklist in your final 48 hours before the exam. If you can tick every box, you are well prepared.
- I can write the lab preparation of HCl, HNO₃, and H₂SO₄ with balanced equations from memory
- I can draw electron dot structures for at least 8 compounds (4 ionic, 4 covalent)
- I know all periodic trends across a period and down a group with explanations
- I can write electrode reactions for electrolysis of acidulated water, CuSO₄ (both electrode types), and molten PbBr₂
- I can solve mole concept numericals using all three relationships (mass, volume, particles)
- I know the general formulae, IUPAC naming rules, and at least 4 reactions each of ethanol and ethanoic acid
- I can identify at least 5 cations using NaOH/NH₄OH tests and 3 gases using their confirmatory tests
- I can explain calcination, roasting, and smelting with one equation each
- I can define pH, write the pH range for acids, bases, and neutral substances, and name 3 indicators
- I have practised at least 3 full previous year papers under timed conditions
Frequently Asked Questions
Q: Which chapter should I study first if I have very little time?
Study of Compounds (HCl, HNO₃, H₂SO₄). It carries the highest weightage (18-20 marks) and follows a predictable pattern: preparation, properties, reactions, and tests. You can cover all three compounds in one focused day and secure roughly a quarter of the paper.
Q: How many equations do I need to memorise for the Chemistry board exam?
Approximately 30-35 equations will cover every major reaction asked in the last 8 years of ICSE papers. This article lists the most critical ones. Write each equation 5 times daily for a week and they will become automatic. Focus on getting the products, states, and conditions (temperature, catalyst) correct.
Q: I find Mole Concept numericals very difficult. How should I approach them?
Start by memorising the four core formulae: moles = mass/molar mass, particles = moles × Avogadro's number, volume at STP = moles × 22.4 L, and vapour density = molar mass/2. Then practise 10 simple problems before moving to multi-step ones. The key is identifying what is given and what is asked, then picking the right formula. Most board exam numericals need only 2-3 steps.
Q: Can I skip Metallurgy and Analytical Chemistry to focus on higher-weightage chapters?
You cannot fully skip them because Section A covers the entire syllabus, and 2-3 questions from these chapters will appear there. However, you can do a surface-level revision: learn 4-5 key equations for Metallurgy (calcination, roasting, thermite, aluminium extraction) and the NaOH/NH₄OH test results for 5-6 cations in Analytical Chemistry. This takes about 2 hours and secures 8-10 easy marks.
Q: What is the best way to study Organic Chemistry for ICSE?
Break it into three parts. First, master IUPAC naming rules with lots of practice (draw 10 structures and name them, name 10 compounds and draw their structures). Second, memorise the functional groups and the compound type each defines. Third, learn the reactions of ethanol and ethanoic acid as a paired set since many reactions mirror each other. IUPAC naming alone can carry 3-4 marks in the exam.
Q: How do I remember which ion gets discharged during electrolysis?
Use the selective discharge rule: at the cathode, the cation lower in the electrochemical series (less reactive) is preferentially discharged. At the anode with inert electrodes, the anion that is a better reducing agent is discharged first. For most board exam problems, remember this simple rule: if H⁺ and a metal ion are present, the less reactive metal ion gets deposited at the cathode (unless it is very reactive like Na⁺ or K⁺, in which case H₂ is evolved).
Q: Are diagrams important in Chemistry? Which ones should I prepare?
Yes, diagrams carry 2-3 marks each and are among the easiest marks on the paper. Prepare these: lab preparation setup for HCl gas, lab preparation setup for HNO₃, electrolysis of acidulated water with labelled electrodes, and the Contact Process flowchart for H₂SO₄. Label every part clearly and use arrows to show gas flow direction.
Chemistry Is a Scoring Subject — If You Prepare Smart
Unlike subjects that require essay writing or subjective interpretation, Chemistry rewards precision. Learn the reactions, practise the numericals, master the diagrams, and the marks follow. Use this guide as your final revision companion, and walk into the exam hall knowing you have every high-weightage topic covered.
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