MG SCHOOL SCIENCE
CHEMISTRY PASSING PACKAGE
Class 10 Science | Important Repeated Concepts
Definitions • Chemical Equations • Important Reactions • Give Reasons
EXAM PREPARATION NOTES01. Chemical Reactions and Equations
Key Definitions
Chemical Reaction
Reactants are converted into products.
Chemical Equation
Symbolic representation of a chemical reaction.
Balanced Chemical Equation
Same number of atoms on LHS and RHS; follows the Law of Conservation of Mass.
Changes in Chemical Reactions:
Change in colour, change in temperature, change in state and evolution of gas.
Important Balanced Chemical Equations
1. H₂ + Cl₂ → 2HCl
2. 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)
3. 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
4. CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat
5. CH₄ + 2O₂ → CO₂ + 2H₂O
6. CaCO₃ → CaO + CO₂
7. Mg + 2HCl → MgCl₂ + H₂
8. Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
9. 3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃
10. Pb(s) + CuCl₂(aq) → PbCl₂(aq) + Cu(s)
11. 2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g)
12. Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
13. ZnCO₃(s) → ZnO(s) + CO₂(g)
14. 2AgCl → 2Ag + Cl₂
15. 2H₂ + O₂ → 2H₂O
16. Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
17. N₂ + 3H₂ → 2NH₃
18. NaCl + AgNO₃ → AgCl + NaNO₃
Types of Chemical Reactions
1. Combination Reaction
Two or more reactants combine to form a single product.
CaO + H₂O → Ca(OH)₂ + Heat
Quicklime to Slaked Lime
C + O₂ → CO₂
Burning of coal.
2H₂ + O₂ → 2H₂O(l)
Formation of water.
2. Decomposition Reaction
A single reactant breaks down into two or more products.
Thermal Decomposition
2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
Crystals lose water when heated and change colour.
Cement Production
CaCO₃ → CaO + CO₂
Calcium oxide is used in the manufacture of cement.
Lead Nitrate Heating
2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
Emission of brown fumes of nitrogen dioxide (NO₂).
Electrolytic Decomposition
2H₂O → 2H₂ + O₂
Cathode: H₂ | Anode: O₂
Photolytic Decomposition
2AgCl → 2Ag + Cl₂
White silver chloride turns grey in sunlight.
2AgBr → 2Ag + Br₂
Used in black and white photography.
3. Oxidation, Reduction and Redox Reactions
Oxidation: Addition of oxygen.
2Cu + O₂ → 2CuO
2Zn + O₂ → 2ZnO
Reduction: Removal of oxygen.
ZnO + C → Zn + CO
Redox Reaction: Oxidation and reduction occur simultaneously in the same reaction.
CuO + H₂ → Cu + H₂O
Oxidised and Reduced Reactants Summary
| Chemical Reaction | Oxidised Substance | Reduced Substance |
|---|---|---|
| Na + O₂ → Na₂O | Na | O₂ |
| CuO + H₂ → Cu + H₂O | H₂ | CuO |
| ZnO + C → Zn + CO | C | ZnO |
Displacement and Double Displacement Reactions
Displacement Reaction:
More reactive element displaces a less reactive element.
Fe + CuSO₄ → FeSO₄ + Cu
Iron displaces copper from copper sulphate as iron is more reactive.
Fe₂O₃ + 2Al → Al₂O₃ + 2Fe
Double Displacement Reaction:
Exchange of ions between reactants.
Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
Precipitation Reaction:
An insoluble substance (precipitate) is formed.
Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
Precipitate: BaSO₄
Ions involved: Ba²⁺ and SO₄²⁻
Energy Changes, Corrosion and Rancidity
Exothermic Reaction
Heat is released.
CaO + H₂O → Ca(OH)₂ + Heat
CH₄ + 2O₂ → CO₂ + 2H₂O
Endothermic Reaction
Heat is absorbed.
CaCO₃ → CaO + CO₂
Corrosion: Metal reacts with atmospheric substances to form undesirable compounds (e.g., rusting of iron).
Rancidity: Change in smell or taste of oil/fat-containing foods due to oxidation.
Prevention of Rancidity: Use antioxidants, refrigerate food, flush packaging with nitrogen gas and store in air-tight containers.
02. Acids, Bases and Salts
Properties of Acids and Bases
| Property | Acids | Bases |
|---|---|---|
| Taste | Sour taste | Bitter taste |
| Ions Produced | Produce H⁺ ions in aqueous solution | Produce OH⁻ ions in aqueous solution |
| Litmus Test | Turns Blue litmus to Red | Turns Red litmus to Blue |
| pH Range | Below 7 (<7) | Above 7 (>7) |
| Examples | HCl, H₂SO₄, HNO₃ | NaOH, KOH, Ca(OH)₂ |
Key Reactions of Acids and Bases
Reaction with Metals:
Acid + Metal → Salt + Hydrogen gas
H₂SO₄ + Zn → ZnSO₄ + H₂
Reaction with Metal Carbonates:
Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
HCl + NaHCO₃ → NaCl + H₂O + CO₂
Reaction with Metal Oxides:
Acid + Metal Oxide → Salt + Water
2HCl + ZnO → ZnCl₂ + H₂O
Neutralization Reaction:
Acid + Base → Salt + Water
NaOH + HCl → NaCl + H₂O
Naturally Occurring Acids
| Source | Naturally Occurring Acid |
|---|---|
| Vinegar | Acetic acid |
| Orange / Lemon | Citric acid |
| Tamarind | Tartaric acid |
| Tomato | Oxalic acid |
| Sour milk (Curd) | Lactic acid |
| Nettle sting / Ant sting | Methanoic acid |
Important pH Values and Definitions
Blood pH7.2 to 7.8
Acid Rain pHBelow 5.6
Strong AcidCompletely dissociates in water.
Weak AcidIncompletely dissociates in water.
Concentrated Acid: High concentration of H⁺ ions OR larger amount of acid in less water.
Dilute Acid: Low concentration of H⁺ ions OR less amount of acid in larger volume of water.
Tooth Decay Causes and Prevention:
Bacteria in mouth convert sugar into acid, causing tooth decay. Basic toothpaste neutralizes acid to prevent decay.
pH Classification of Salts
| Salt Type | Combination | pH Level | Example |
|---|---|---|---|
| Neutral Salt | Strong Acid + Strong Base | pH = 7 | NaCl |
| Acidic Salt | Strong Acid + Weak Base | pH < 7 | NH₄Cl |
| Basic Salt | Weak Acid + Strong Base | pH > 7 | Na₂CO₃ |
Chlor-Alkali Process and Industrial Chemicals
2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
Brine SolutionAqueous solution of sodium chloride.
NaOH UsesSoaps, detergents and paper making.
Cl₂ UsesWater treatment, swimming pools and PVC manufacture.
H₂ UsesRocket fuel and margarine.
Important Chemical Compounds
| Common Name | Chemical Name | Formula | Key Uses |
|---|---|---|---|
| Washing Soda | Sodium carbonate | Na₂CO₃ | Manufacture of borax, softening hard water |
| Baking Soda | Sodium hydrogen carbonate | NaHCO₃ | Antacid, ingredient in baking powder |
| Bleaching Powder | Calcium oxychloride | CaOCl₂ | Bleaching clothes, oxidizing agent, disinfecting water |
| Plaster of Paris | Calcium sulphate Hemihydrate | CaSO₄·½H₂O | Plastering fractured bones, making toys and decorative items |
Water of Crystallisation:
Fixed number of water molecules present in one formula unit of a salt (e.g., CuSO₄·5H₂O has 5 water molecules).
Marble and Limestone Formula: Calcium carbonate (CaCO₃).
Soil Treatment: Farmers treat acidic soil with slaked lime (Ca(OH)₂) when soil acidity increases.
03. Metals and Non-Metals
Physical and Chemical Properties
| Property | Metals | Non-Metals |
|---|---|---|
| Sonorous | Yes (produces ringing sound) | No |
| Ductility | Ductile (can be drawn into thin wire; Gold is most ductile) | Non-ductile |
| Malleability | Malleable (can be beaten into thin sheets) | Non-malleable |
| Lustre | Lustrous (shiny surface) | Non-lustrous |
| Electrical and Heat Conductivity | Good conductors of heat and electricity | Poor conductors |
| Reaction with Dilute Acids | Liberates H₂ gas from dilute acids | Does not liberate H₂ gas |
| Nature of Oxides | Basic in nature | Acidic in nature |
| Electrochemical Nature | Electropositive | Electronegative |
Special Concepts and Ionic Compounds
Amphoteric Oxides:
Metal oxides that react with both acids and bases to produce salt and water.
Examples: Al₂O₃, ZnO.
Ionic Compounds:
Compounds formed by the transfer of electrons from a metal to a non-metal.
Formation of NaCl
Properties of Ionic Compounds:
- Hard and brittle.
- High melting and boiling points due to strong inter-ionic electrostatic forces.
- Soluble in water, insoluble in organic solvents.
- Conduct electricity in molten/solution state, not in solid state due to fixed ions.
Extraction of Zinc
Roasting (Sulphide Ore):
Heating sulphide ore strongly in presence of excess air.
2ZnS + 3O₂ → 2ZnO + 2SO₂
Calcination (Carbonate Ore):
Heating carbonate ore strongly in presence of limited air.
ZnCO₃ → ZnO + CO₂
Reduction:
Reducing metal oxide using carbon/coke.
ZnO + C → Zn + CO
Corrosion, Prevention and Alloys
Corrosion Definition:
Attack on metals by atmospheric substances to form undesirable compounds.
Rusting of IronIron reacts with atmospheric substances.
CopperForms green coat of Copper Carbonate.
SilverTurns black due to Silver Sulphide.
Corrosion Prevention:
Painting, oiling, greasing, galvanising, chrome plating, anodising and alloy formation.
Galvanising:
Process of coating iron/steel with a thin layer of Zinc to prevent rusting.
Alloys Definition:
Homogeneous mixture of two or more metals (or metal and non-metal).
Common Alloys
| Alloy | Composition |
|---|---|
| Brass | Copper + Zinc |
| Bronze | Copper + Tin |
| Solder | Lead + Tin |
Liquid Elements at Room Temperature:
Mercury (Liquid metal), Bromine (Liquid non-metal).
Scientific Reasoning – Give Reasons Questions
Q1. Metals are used in making cooking vessels?
Answer: Metals are good conductors of heat, have high melting points, and possess high malleability.
Q2. Sodium metal is stored in kerosene?
Answer: Sodium reacts vigorously with atmospheric oxygen and moisture, but does not react with kerosene.
Q3. Calcium reaction with water does not catch fire?
Answer: The reaction of calcium with water is less violent; heat evolved is insufficient for hydrogen to catch fire.
Q4. Ionic compounds have high melting and boiling points?
Answer: They have strong electrostatic forces of attraction between oppositely charged ions requiring high energy to break.
Q5. H₂ gas is not liberated when metal reacts with concentrated HNO₃?
Answer: Concentrated HNO₃ is a strong oxidizing agent; it oxidizes the H₂ produced into water (H₂O).
Q6. ZnO and Al₂O₃ are called amphoteric oxides?
Answer: They react with both acids and bases to yield salt and water.
Q7. Gold is used to make jewellery?
Answer: Gold is lustrous, highly ductile, malleable, and extremely unreactive (least reactive metal).
Q8. Solid ionic compounds do not conduct electricity?
Answer: In solid state, ions are held in fixed positions and cannot move freely.
04. Carbon and Its Compounds
Bonding and Versatile Nature of Carbon
Covalent Bond
Sharing of electrons between two atoms.
Ionic Bond
Transfer of electrons from one atom to another.
Catenation
Carbon's unique ability to form bonds with other carbon atoms, creating long chains or rings.
Tetravalency
Carbon has 4 valence electrons and can bond with 4 other atoms.
Why C⁴⁺ cannot form:
Removing 4 electrons requires a massive amount of energy.
Why C⁴⁻ cannot form:
6 protons in the nucleus cannot hold 10 electrons easily.
Classification of Hydrocarbons
| Hydrocarbon Type | Bonding | General Formula | First Member | Flame Character |
|---|---|---|---|---|
| Alkanes (Saturated) | Single bond (C–C) | CāH₂ā₊₂ | Methane (CH₄) | Clean blue flame |
| Alkenes (Unsaturated) | Double bond (C=C) | CāH₂ā | Ethene (C₂H₄) | Yellow smoky flame |
| Alkynes (Unsaturated) | Triple bond (C≡C) | CāH₂ā₋₂ | Ethyne (C₂H₂) | Yellow smoky flame |
Functional Groups and Isomerism
| Functional Group | Symbol |
|---|---|
| Alcohol | –OH |
| Aldehydes | –CHO |
| Ketone | C=O |
| Carboxylic Acid | –COOH |
Structural Isomers:
Compounds with the same molecular formula but different structural formulas.
Example: n-butane and isobutane.
Chemical Reactions of Carbon Compounds
Oxidation:
Alcohols are oxidized to carboxylic acids using alkaline KMnO₄ or acidified K₂Cr₂O₇.
Addition Reaction / Hydrogenation:
Hydrogen added to unsaturated hydrocarbons using Nickel (Ni) or Palladium catalyst to produce saturated fats.
Unsaturated oil + H₂ → Saturated fat
Substitution Reaction:
Hydrogen atoms of a hydrocarbon are replaced by other atoms.
CH₄ + Cl₂ → CH₃Cl + HCl
Combustion Reaction:
Burning carbon compounds in air to produce CO₂, heat and light.
2CH₃OH + 3O₂ → 4H₂O + 2CO₂
Important Carbon Compounds and Processes
Ethanol Uses and Reactions:
Used in alcoholic drinks, tincture iodine and medicines. Concentrated H₂SO₄ acts as a dehydrating agent removing water from ethanol.
Ethanoic Acid (Glacial Acetic Acid):
Pure ethanoic acid has a melting point of 290 K and freezes in winter, earning the name Glacial Acetic Acid.
Esterification:
Reaction between carboxylic acid and alcohol to form pleasant-smelling esters (used in perfumes and flavouring agents).
Saponification:
Reaction of alkaline base with long-chain carboxylic acid to form soap.
Soaps:
Sodium salts of long-chain fatty acids; forms micelles with oil/dirt; does not lather in hard water.
Detergents:
Sodium/Potassium salts of sulphonic acids; forms lather in both hard and soft water.
Formula and Molecular Structures Summary
| Compound Name | Molecular Formula | Structural Notes |
|---|---|---|
| Cyclohexane | C₆H₁₂ | Cyclic alkane ring with single bonds |
| Benzene | C₆H₆ | Aromatic ring with alternating double bonds |
| Propyne | C₃H₄ | Three-carbon alkyne with one triple bond |
| Butane | C₄H₁₀ | Four-carbon alkane (straight and branched isomers) |
| Propanoic Acid | C₃H₆O₂ | Three-carbon carboxylic acid (–COOH) |
| Pentane | C₅H₁₂ | Five-carbon alkane |
Electron Dot Structure Requirements
MethaneCH₄
EtheneC₂H₄
Oxygen MoleculeO₂
Hydrogen MoleculeH₂
Nitrogen MoleculeN₂
Important: Practise drawing the electron dot structures of all five molecules listed above.
EXAM PREPARATION TIP
Revise all important definitions, balanced chemical equations, chemical properties, tables, formulas and Give Reasons questions. Practise writing chemical equations and electron dot structures.
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