2021

• Which group of elements had not been discovered when Mendeleev’s version of the periodic table was published?[1 mark]

  ✅ Answer:

  • Group 0 (noble gases)
• What Is Meant by ‘Isotopes’? (Referring to Subatomic Particles)

  • Atoms with the same number of protons,
  • But with different numbers of neutrons.
• Give the colour change when nitric acid is added to the mixture of universal indicator and water.

  ✅ Answer: Green to red

  • Universal indicator in neutral water is green.
  • Adding nitric acid (a strong acid) turns it red (low pH).
• What happens to the pH of water when nitric acid is added?

  ✅ Answer: Decreases

  • Acids release H⁺ ions, which lower the pH of the solution.
• state symbol of nitric acid

  aq
• Two Observations When Zinc Carbonate Reacts with Nitric Acid:

  1. White solid dissolves (until excess is added, then some remains at the bottom).
  2. Fizzing / bubbles of gas are seen (carbon dioxide is produced).
• Correct formula for zinc nitrate:Zn(NO₃)₂

  Reason:Zinc is Zn²⁺, nitrate is NO₃⁻.You need 2 NO₃⁻ to balance 1 Zn²⁺.
• Method to Make Pure, Dry Copper Chloride Crystals:

  • Warm dilute hydrochloric acid in a beaker.
  • Add copper oxide slowly and stir.
  • Continue adding until no more dissolves (excess copper oxide).
  • Filter the mixture to remove excess copper oxide.
  • Transfer the filtered solution to an evaporating dish.
  • Heat gently to evaporate water and leave dry copper chloride crystals.
• What is the formula of Buckminsterfullerene?

  ✅ Answer: C₆₀
• Explain why graphite conducts electricity.

  ✅ Answer:

  • Graphite has delocalised electrons.
  • These electrons carry electrical charge through the structure.
• Why steel is harder than iron:

  • Carbon atoms are a different size to iron atoms.
  • This distorts the layers of iron atoms.
  • The layers can't slide over each other easily.
• What type of reaction happens at the negative electrode?Give the reason for your answer.(2 marks)

  Answer:Type of reaction: ReductionReason: Because H⁺ ions gain electrons.
• Explain how oxygen gas is produced in the electrolysis of sodium sulfate solution.(4 marks)

  Answer:

  • Water molecules break down into H⁺ and OH⁻ ions.
  • OH⁻ ions move to the positive electrode (anode).
  • At the anode, OH⁻ ions are oxidised.
  • This forms oxygen gas and water.
• Order of Alkanes (by number of carbon atoms):

  1. Methane – CH₄ (1 carbon)
  2. Ethane – C₂H₆ (2 carbons)
  3. Propane – C₃H₈ (3 carbons)
  4. Butane – C₄H₁₀ (4 carbons)