2022 p1 (without question 5, 7, 9 + 10)

• Universal indicator paper is used to determine the pH. Explain why litmus paper would not be a suitable indicator to use in this experiment.

  Litmus paper only shows if the solution is acidic or alkaline not how acidic or alkaline the solution is
• State two reasons why the actual yield of a reaction is usually less than the theoretical yield

  Some reactants remain unreacted. Some product is lost during the reaction. Side reactions occur.
• One step in the extraction of titanium metal involves the displacement reaction between titanium chloride, TiCl4 + 2Mg → Ti + 2MgCl2 This equation can be simplified as Ti4+ + 2Mg → Ti + 2Mg2+ Explain why this displacement reaction can be described as a redox reaction

  Redox involves both reduction and oxidation. Magnesium loses electrons - oxidised. Titanium ions accept electrons - reduced.
• Phytoextraction is an alternative biological method that can be used to extract metals from very low-grade ores. Give one disadvantage of phytoextraction as a method of extraction of metals.

  Slow process, expensive
• Copper is low down in the reactivity series and can be obtained from copper oxide. Devise a simple method to obtain a sample of copper from copper oxide in the laboratory.

  Mix copper oxide with carbon and then heat strongly until no further change
• Why would graphene be a good conductor of an electric current?

  Carbon has 4 outer shell electrons, 3 are used in bond with other carbon atoms so one electron is free to move
• Potassium chloride has a melting point of 770°C. Explain why potassium chloride has a high melting point.

  There are strong forces of attraction between ions of opposite charge so a large amount of energy is needed to overcome them
• When metal Y reacts with dilute sulfuric acid, bubbles form quickly at first and then the reaction stops. Most of the solid metal remains. Explain why the reaction between metal Y and excess dilute sulfuric acid stopped even though there was solid metal Y left.


  Metal sulfate coats the metal forming a barrier. This prevents further reaction of metal with acid.
• Explain the meaning of the term weak acid

  It is partially ionised meaning there are fewer H+ ions than expected