chemical changes

• What happens during a chemical change?

  New substances are formed, irreversible change
• What do chemical changes involve?

  Making and breaking of chemical bonds
• What do acids release in solution?

  Hydrogen ions (H⁺)
• How do strong acids behave in water?

  They completely ionise in water
• How do weak acids behave in water?

  They partially ionise in water
• What do bases do to acids?

  Neutralise acids to form salt and water
• What are alkalis?

  Soluble bases that release OH⁻ ions
• What is the pH range for acids, neutrals, and alkalis?

  • Acids: 0 - 6
  • Neutral: 7
  • Alkalis: 8 - 14
• What is the neutralisation reaction formula?

  Acid + Base → Salt + Water
• What does the pH scale measure?

  Acidity or alkalinity
• How do indicators function?

  Change colour depending on pH
• What are the colours of common indicators at different pH levels?

  • Litmus: Red (acid), Purple (neutral), Blue (alkali)
  • Methyl Orange: Red (acid), Yellow (neutral), Yellow (alkali)
  • Phenolphthalein: Colourless (acid), Colourless (neutral), Pink (alkali)
• What does the Universal Indicator show?

  A full range of colours for pH values
• What is the reaction of an acid with a metal?

  Acid + Metal → Salt + Hydrogen
• How do more reactive metals behave with acids?

  They react faster with acids
• How can you test for hydrogen gas?

  Use a lit splint for a "Pop" sound
• What is the reaction of an acid with a metal oxide?

  Acid + Metal Oxide → Salt + Water
• What does the reaction of an acid with a metal oxide form?

  A neutral solution
• What is the reaction of an acid with a metal carbonate?

  Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
• How can you test for carbon dioxide?

  Bubble gas through limewater to go cloudy
• What is the reactivity series?

  Metals react differently with acids, water, oxygen
• How do metals react with acids and water?

  • Potassium (K): Violent with acid and explosive with water
  • Sodium (Na): Violent with acid and rapid with water
  • Calcium (Ca): Fizzes with acid and slow with water
  • Magnesium (Mg): Reacts with acid, no reaction with water
  • Copper (Cu): No reaction with acid or water
• What are displacement reactions?

  A more reactive metal displaces a less reactive metal
• What is a redox reaction?

  Involves oxidation and reduction of metals
• What happens to magnesium in a redox reaction?

  Magnesium is oxidised to Mg²⁺
• What happens to copper in a redox reaction?

  Copper is reduced to Cu
• How can metals below carbon be extracted?

  By heating with carbon
• How are reactive metals extracted?

  By electrolysis
• What is electrolysis?

  Uses electricity to split a compound
• What is required for electrolysis?

  A molten or dissolved ionic compound
• What happens to positive ions during electrolysis?

  They move to the negative electrode
• What happens to negative ions during electrolysis?

  They move to the positive electrode
• What happens to lead ions during electrolysis?

  Lead gains electrons at the cathode
• What happens to bromine ions during electrolysis?

  Bromine loses electrons at the anode
• What are the rules for aqueous electrolysis at the cathode?

  If metal is more reactive than hydrogen, hydrogen is produced
• What are the rules for aqueous electrolysis at the anode?

  If halide ions are present, halogen is produced
• What is produced during the electrolysis of NaCl solution?

  Hydrogen and chlorine gases
• What are the summary reactions of acids?

  • Acid + Metal: HCl + Mg → MgCl₂ + H₂ (H₂ produced)
  • Acid + Metal Oxide: H₂SO₄ + CuO → CuSO₄ + H₂O (No gas produced)
  • Acid + Metal Carbonate: HCl + CaCO₃ → CaCl₂ + H₂O + CO₂ (CO₂ produced)
  • Electrolysis of NaCl: Produces H₂ and Cl₂