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