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GCSE Chemistry Notes

GCSE Chemistry Notes

Unit 2 Overview

  • Subject: Chemical Bonding, Application of Chemical Reactions, Organic Chemistry

  • Exam Duration: 1 hour 45 minutes (45% of qualification)

  • Topics Included:

    • 2.1 Bonding, structure, and properties

    • 2.2 Acids, bases, and salts

    • 2.3 Metals and their extraction

    • 2.4 Chemical reactions and energy

    • 2.5 Crude oil, fuels, and organic chemistry

    • 2.6 Reversible reactions, industrial processes, and important chemicals

2.1 Bonding, Structure, and Properties

Key Concepts

  • Properties of Compounds: Metals, ionic compounds, simple molecular covalent substances, giant covalent substances.

  • Electronic Structure and Bonding:

    • Ionic Bonding: Transfer of electrons represented via dot and cross diagrams.

    • Covalent Bonds: Sharing of electrons in molecules illustrated with dot and cross diagrams.

    • Intermolecular Forces: Discussing simple molecular structures.

Metal Properties

  • High Melting/Boiling Points: Due to strong metallic bonds; they conduct heat/electricity (electrons are free to move).

  • Properties of Specific Carbons:

    • Diamond: Very hard (4 covalent bonds per carbon).

    • Graphite: Soft and conducts electricity; atoms arranged in layers with delocalised electrons.

    • Carbon Nanotubes: High strength, electricity conduction; used in electronics and materials.

    • Fullerenes: Spherical structures (e.g., Buckminsterfullerene), can encapsulate other molecules.

Nanoscience

  • Use of nano-scale silver and titanium dioxide: Antibacterial and UV absorption properties, risks concerning long-term effects on health and environment.

2.2 Acids, Bases, and Salts

Definitions & Reactions

  • pH Scale: Identifying substances as acidic, alkaline, or neutral.

  • Acids produce H+ ions; alkalies yield OH- ions.

Reactions

  • Neutralization: H+(aq) + OH^-(aq) → H₂O(l)

  • Metal Reactions: Includes simple reactions between dilute acids and various metals.

  • Identifying Functional Groups: Test methods such as adding barium chloride to detect sulfate ions and hydrochloric acid for carbonates.

Fertiliser Production

  • Produced through neutralization of ammonia with acids (e.g., ammonium sulfate and ammonium nitrate).

  • Eutrophication: Impact of fertilizer runoff on water bodies.

2.3 Metals and Their Extraction

Extraction Methods

  • Metals found in ores; extraction depends on metal reactivity (e.g., electrolysis for reactive metals).

  • Blast Furnace for Iron: Combines iron ore with coke and limestone to produce iron; reactions include:

    • Iron Oxide reduction by carbon monoxide: Fe₂O₃ + 3CO → 2Fe + 3CO₂.

  • Haber Process: Ammonia production via the reaction of nitrogen and hydrogen.

Environmental Impacts

  • Discussion on metal mining, habitat destruction, metal waste, and the economic factors influencing extraction processes.

2.4 Chemical Reactions and Energy

Reaction Types

  • Exothermic Reactions: Produce heat (e.g., combustion).

  • Endothermic Reactions: Absorb heat.

Activation Energy

  • Is the minimum energy required for a reaction to occur, often visualized through energy profile diagrams, illustrating energy changes between reactants and products.

Bond Energies

  • Using bond energy values to calculate overall reaction energy changes to identify whether a reaction is exothermic or endothermic.

2.5 Crude Oil, Fuels, and Organic Chemistry

Overview of Crude Oil

  • Composed of a mixture of hydrocarbons formed via the decomposition of marine organisms over millions of years.

  • Fractional Distillation: Separation process based on boiling points: gasoline, kerosene, diesel, etc.

Hydrocarbon Properties

  • Trends in physical properties (e.g., viscosity, ignition quality, color) as chain length increases.

Hydrogen as Fuel

  • Hydrogen combustion produces only water; advantages include environmental cleanliness, while disadvantages involve production energy costs and storage concerns.

2.6 Reversible Reactions, Industrial Processes, and Important Chemicals

Important Processes

  • Haber Process for Ammonia: Industrial production method involving reversible reactions.

  • Contact Process for Sulfuric Acid: Production through oxidizing sulfur dioxide to sulfur trioxide.

Fertiliser Production

  • Discusses benefits and environmental impacts of nitrogen-rich fertilizers, e.g., nitrogen runoff leading to eutrophication of aquatic ecosystems.

Chemical Tests

  • Methods for detecting various ions, conducting flame tests, and colorimetric tests for organic compounds.

Chemical Tests

Tests for Gases and Ions

  • Hydrogen: Squeaky pop test.

  • Oxygen: Relights glowing splint.

  • Ammonia: Turns damp litmus blue.

  • Sulfate Test: Precipitate formed when barium chloride reacts with a sulfate ion.

Summary of Key Reactions and Their Equations

Key Chemical Equations

  • Ammonia production from nitrogen and hydrogen:

    • N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

  • Synthesis of sulfuric acid via Contact Process:

    • S + O₂ → SO₂

    • 2SO₂ + O₂ ⇌ 2SO₃

    • SO₃ + H₂O → H₂SO₄