Chemistry

---
name: chemistry
description: >-
  CBSE Grade 10 Chemistry — Chemical Reactions, Acids/Bases, Metals, Carbon Compounds.
  Activate for chemistry concepts, equations, reactions, and board exam preparation.
---

# Chemistry — CBSE Grade 10 Science

## Syllabus Coverage (2026–27)

| Unit | Chapters | Marks |
|------|----------|-------|
| I. Chemical Substances – Nature and Behaviour | Ch 1: Chemical Reactions and Equations | 25 |
| | Ch 2: Acids, Bases and Salts | (combined) |
| | Ch 3: Metals and Non-metals | |
| | Ch 4: Carbon and its Compounds | |
| **Chemistry Total** | **4 Chapters** | **~25** |

---

## Chapter 1: Chemical Reactions and Equations

### Key Concepts
- Chemical equation writing and balancing
- Types of reactions: Combination, Decomposition, Displacement, Double Displacement, Redox
- Oxidation (gain of oxygen / loss of hydrogen) and Reduction (loss of oxygen / gain of hydrogen)
- Exothermic and Endothermic reactions
- Corrosion and Rancidity

### Important Chemical Equations (MUST memorize)
```
COMBINATION:
  2Mg(s) + O₂(g) → 2MgO(s)                     [Burning magnesium]
  CaO(s) + H₂O(l) → Ca(OH)₂(aq)                [Quick lime + water]
  C(s) + O₂(g) → CO₂(g)                          [Burning carbon]

DECOMPOSITION:
  2FeSO₄(s) →heat→ Fe₂O₃(s) + SO₂(g) + SO₃(g)  [Thermal decomposition]
  CaCO₃(s) →heat→ CaO(s) + CO₂(g)               [Limestone heating]
  2Pb(NO₃)₂(s) →heat→ 2PbO(s) + 4NO₂(g) + O₂(g) [Lead nitrate]
  2AgCl(s) →sunlight→ 2Ag(s) + Cl₂(g)            [Photolytic decomposition]
  2H₂O(l) →electricity→ 2H₂(g) + O₂(g)          [Electrolytic decomposition]

DISPLACEMENT:
  Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)         [Iron displaces copper]
  Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)         [Zinc displaces copper]

DOUBLE DISPLACEMENT:
  Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s)↓ + 2NaCl(aq) [Precipitation]
  NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)         [Neutralization]

REDOX:
  CuO(s) + H₂(g) → Cu(s) + H₂O(l)
  [CuO: reduced (lost O), H₂: oxidized (gained O)]
  
  MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂
  [MnO₂: oxidizing agent, HCl: reducing agent]
```

### Common Exam Traps
- **Not writing state symbols** (s), (l), (g), (aq) — marks deducted for this
- Not balancing equations properly
- Confusing oxidation and reduction
- Not identifying type of reaction correctly

---

## Chapter 2: Acids, Bases and Salts

### Key Concepts
- Acid: produces H⁺ ions in water; Base: produces OH⁻ ions in water
- pH scale: 0-14; pH < 7 acidic, pH = 7 neutral, pH > 7 basic
- Indicators: litmus, methyl orange, phenolphthalein
- Reactions of acids and bases with metals, metal oxides, metal carbonates
- Neutralization reaction
- Important salts: NaOH, NaHCO₃, Na₂CO₃, bleaching powder, plaster of Paris, baking soda

### Important Reactions
```
ACID + METAL → Salt + Hydrogen gas
  2HCl(aq) + Zn(s) → ZnCl₂(aq) + H₂(g)↑

ACID + METAL CARBONATE → Salt + H₂O + CO₂
  2HCl(aq) + Na₂CO₃(s) → 2NaCl(aq) + H₂O(l) + CO₂(g)↑

ACID + METAL HYDROGEN CARBONATE → Salt + H₂O + CO₂
  HCl(aq) + NaHCO₃(s) → NaCl(aq) + H₂O(l) + CO₂(g)↑

ACID + BASE → Salt + Water (Neutralization)
  NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

ACID + METAL OXIDE → Salt + Water
  2HCl(aq) + CuO(s) → CuCl₂(aq) + H₂O(l)

BASE + NON-METAL OXIDE → Salt + Water
  2NaOH(aq) + CO₂(g) → Na₂CO₃(aq) + H₂O(l)
```

### Important Salts and Formulas
```
COMMON SALT: NaCl (Sodium chloride)
  Source: Sea water, rock salt deposits

BAKING SODA: NaHCO₃ (Sodium hydrogen carbonate)
  Uses: antacid, fire extinguisher, baking

WASHING SODA: Na₂CO₃·10H₂O (Sodium carbonate decahydrate)
  Preparation: NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl
               2NaHCO₃ →heat→ Na₂CO₃ + H₂O + CO₂

BLEACHING POWDER: Ca(OCl)Cl / CaOCl₂ (Calcium oxy-chloride)
  Preparation: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

PLASTER OF PARIS: CaSO₄·½H₂O (Calcium sulphate hemihydrate)
  Preparation: CaSO₄·2H₂O →373K→ CaSO₄·½H₂O + 1½H₂O
  Setting: CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O (exothermic)

CHLOR-ALKALI PROCESS:
  2NaCl(aq) + 2H₂O(l) →electrolysis→ 2NaOH(aq) + Cl₂(g) + H₂(g)
  At anode: Cl₂    At cathode: H₂    Near cathode: NaOH
```

### pH Scale Reference
```
pH 0-1: Strong acid (HCl, H₂SO₄)
pH 2-3: Weak acid (vinegar, lemon juice)
pH 4-6: Slightly acidic (tomato, coffee, rain water)
pH 7: Neutral (pure water)
pH 8-9: Slightly basic (baking soda, blood)
pH 10-11: Weak base (milk of magnesia)
pH 12-14: Strong base (NaOH, KOH)

Body context:
  Stomach: pH 1.5-3.5 (HCl)
  Blood: pH 7.35-7.45
  Tooth enamel decays below pH 5.5
```

### Common Exam Traps
- Confusing NaHCO₃ (baking soda) with Na₂CO₃ (washing soda)
- Not writing water of crystallization correctly
- Forgetting the chlor-alkali process products
- pH of blood, stomach, rain water — frequently asked MCQs

---

## Chapter 3: Metals and Non-metals

### Key Concepts
- Physical properties of metals vs non-metals
- Reactivity series
- Extraction of metals (based on reactivity)
- Corrosion and its prevention
- Ionic bonding: electron transfer

### Reactivity Series (MUST memorize)
```
Most Reactive → Least Reactive:
K > Na > Ca > Mg > Al > Zn > Fe > Ni > Sn > Pb > [H] > Cu > Hg > Ag > Au > Pt

Mnemonic: "King Nathu Can Make A Zoo In Nagpur Since Pankaj Has Cupboard Having Silver And Gold Plus Platinum"

KEY RULE:
- More reactive metal displaces less reactive metal from its salt solution
- Metals above hydrogen react with dilute acids to produce H₂
- Metals below hydrogen do NOT react with dilute acids
```

### Extraction Methods (Based on Reactivity)
```
HIGH REACTIVITY (K, Na, Ca, Mg, Al):
  → Electrolytic reduction
  Example: 2Al₂O₃ →electrolysis→ 4Al + 3O₂ (with cryolite Na₃AlF₆)

MEDIUM REACTIVITY (Zn, Fe, Ni, Sn, Pb):
  → Reduction with carbon (smelting)
  Example: ZnO + C → Zn + CO
           Fe₂O₃ + 3C → 2Fe + 3CO

LOW REACTIVITY (Cu, Hg, Ag, Au):
  → Self-reduction or just heating in air
  Example: 2HgS + 3O₂ → 2HgO + 2SO₂
           2HgO →heat→ 2Hg + O₂

STEPS IN EXTRACTION:
1. Mining (dig ore from earth)
2. Enrichment/Concentration (remove impurities)
3. Roasting (heat sulphide ore in air → oxide)
   2ZnS + 3O₂ → 2ZnO + 2SO₂
4. Calcination (heat carbonate ore → oxide)
   ZnCO₃ → ZnO + CO₂
5. Reduction (oxide → metal)
6. Refining (electrolytic refining for purity)
```

### Ionic Bonding
```
Na → Na⁺ + e⁻ (loses 1 electron)
Cl + e⁻ → Cl⁻ (gains 1 electron)
Na⁺Cl⁻ → NaCl (ionic compound)

Properties of ionic compounds:
- High melting and boiling point
- Soluble in water
- Conduct electricity in molten/aqueous state (NOT solid)
- Hard but brittle
```

### Common Exam Traps
- Not remembering the exact order of reactivity series
- Confusing roasting (sulphide → oxide) with calcination (carbonate → oxide)
- Not mentioning cryolite in aluminium extraction
- Forgetting that ionic compounds don't conduct electricity in solid state

---

## Chapter 4: Carbon and its Compounds

### Key Concepts
- Covalent bonding in carbon compounds
- Allotropes: diamond, graphite, buckminsterfullerene
- Hydrocarbons: saturated (alkanes) and unsaturated (alkenes, alkynes)
- Homologous series
- Functional groups
- Nomenclature (IUPAC naming)
- Chemical properties: combustion, oxidation, addition, substitution
- Ethanol and Ethanoic acid — properties and reactions
- Soaps and detergents

### Homologous Series
```
ALKANES (CₙH₂ₙ₊₂) — Single bonds — Saturated
  CH₄ (Methane), C₂H₆ (Ethane), C₃H₈ (Propane), C₄H₁₀ (Butane), C₅H₁₂ (Pentane)

ALKENES (CₙH₂ₙ) — One double bond — Unsaturated
  C₂H₄ (Ethene), C₃H₆ (Propene), C₄H₈ (Butene)

ALKYNES (CₙH₂ₙ₋₂) — One triple bond — Unsaturated
  C₂H₂ (Ethyne/Acetylene), C₃H₄ (Propyne)
```

### Functional Groups
```
| Group | Formula | Name Suffix | Example |
|-------|---------|------------|---------|
| Alcohol | -OH | -ol | Ethanol (C₂H₅OH) |
| Aldehyde | -CHO | -al | Ethanal (CH₃CHO) |
| Ketone | >C=O | -one | Propanone (CH₃COCH₃) |
| Carboxylic acid | -COOH | -oic acid | Ethanoic acid (CH₃COOH) |
| Halide | -X (Cl,Br) | -chloro/-bromo | Chloromethane (CH₃Cl) |
```

### Important Reactions
```
COMBUSTION:
  CH₄ + 2O₂ → CO₂ + 2H₂O + heat (complete)
  2CH₄ + 3O₂ → 2CO + 4H₂O (incomplete — forms soot)

OXIDATION OF ETHANOL:
  CH₃CH₂OH + [O] →alkaline KMnO₄→ CH₃COOH
  (Ethanol → Ethanoic acid)

ADDITION REACTION (unsaturated → saturated):
  CH₂=CH₂ + H₂ →Ni catalyst→ CH₃-CH₃
  (Ethene + Hydrogen → Ethane)
  CH₂=CH₂ + Br₂ → CH₂Br-CH₂Br (decolourizes bromine water — TEST for unsaturation)

SUBSTITUTION REACTION (saturated):
  CH₄ + Cl₂ →sunlight→ CH₃Cl + HCl
  (Methane + Chlorine → Chloromethane)

ESTERIFICATION:
  CH₃COOH + C₂H₅OH →acid catalyst→ CH₃COOC₂H₅ + H₂O
  (Ethanoic acid + Ethanol → Ethyl ethanoate — fruity smell)

SAPONIFICATION:
  Fat/Oil + NaOH → Soap + Glycerol
```

### Ethanol Properties
```
Formula: C₂H₅OH or CH₃CH₂OH
Boiling point: 78°C
- Reacts with Na: 2Na + 2C₂H₅OH → 2C₂H₅ONa + H₂↑
- Dehydration: C₂H₅OH →conc.H₂SO₄, 443K→ C₂H₄ + H₂O
- Oxidation: →KMnO₄→ CH₃COOH
```

### Ethanoic Acid Properties
```
Formula: CH₃COOH (Acetic acid, vinegar has 5-8%)
Melting point: 17°C (freezes in winter → "glacial" acetic acid)
- Reacts with NaHCO₃: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂↑
- Reacts with NaOH: CH₃COOH + NaOH → CH₃COONa + H₂O
- Esterification with Ethanol (see above)
```

### Soaps and Detergents
```
SOAP:
  - Sodium/potassium salt of long-chain fatty acid
  - Example: C₁₇H₃₅COONa (Sodium stearate)
  - Doesn't work in hard water (forms scum with Ca²⁺/Mg²⁺)

DETERGENT:
  - Sodium salt of sulphonic acid
  - Works in both hard and soft water
  - Example: CH₃(CH₂)₁₁C₆H₄SO₃Na

MICELLE FORMATION:
  - Hydrophobic tail → dissolves in grease/oil
  - Hydrophilic head → dissolves in water
  - Forms spherical structure trapping oil in center
```

### Common Exam Traps
- Not naming compounds correctly (IUPAC naming errors)
- Confusing addition and substitution reactions
- Not knowing the test for unsaturation (bromine water decolourization)
- Writing wrong product in esterification
- Forgetting that soap doesn't work in hard water

---

## High-Yield Topics (495+ Strategy)
1. **Chemical Equations** — Balancing and identifying reaction types (guaranteed 3-5M)
2. **Carbon Compounds** — Naming, reactions, functional groups (5M LA likely)
3. **Acids, Bases and Salts** — pH, salt preparation (3-5M)
4. **Metals and Non-metals** — Reactivity series, extraction (3-5M)

## Answer Writing Framework for Chemistry
1. **Always write balanced equations with state symbols**
2. **Name the type of reaction** in every equation-based answer
3. **Use proper chemical names** alongside formulas
4. **For salt preparation questions** — write the method, equation, and conditions
5. **Draw electron dot structures** whenever asked about bonding
6. **Test for gases**: CO₂ (turns lime water milky), H₂ (burns with pop sound), O₂ (relights glowing splint)