IGCSE Chemistry 2020 0620/43 May/June

IGCSE 2020 0620/43 May/June (pdf)

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1. (a) The structures of five organic compounds, A, B, C, D and E, are shown.
   Answer the questions that follow.
   Each letter may be used once, more than once or not at all.
   (i) Give the letter of the compound that is propan-1-ol.
   (ii) Give the letter of the compound that has the empirical formula CH₂.
   (iii) Give the letter of one compound that reacts with bromine in an addition reaction.
   (iv) Give the letter of one compound that reacts with chlorine to form the compound shown.
   (i) Give the letter of the compound that is propan-1-ol.
   (ii) Give the letter of the compound that has the empirical formula CH₂.
   (iii) Give the letter of one compound that reacts with bromine in an addition reaction.
   (iv) Give the letter of one compound that reacts with chlorine to form the compound shown.
   (viii) Draw a structural isomer of compound D.
   Show all of the atoms and all of the bonds.
   (b) Some acids are described as weak acids.
   State the meaning of the term weak acid.
   
2. Ammonia is manufactured by the Haber process.
   (a) The equation for the reaction is shown.
   N₂(g) + 3H₂(g) ⇄ 2NH₃(g)
   (i) State what is meant by the symbol ⇄.
   (ii) State one source of hydrogen used in the manufacture of ammonia.
   (b) The table shows some data for the production of ammonia.
   Deduce the effect on the percentage yield of ammonia of:
   

• increasing the pressure of the reaction
  
• increasing the temperature of the reaction.
  (c) Explain, in terms of particles, what happens to the rate of this reaction when the temperature is increased.
  (d) Ammonia, NH₃, is used to produce nitric acid, HNO₃. This happens in a three-stage process.
  Stage 1 is a redox reaction.
  4NH₃ + 5O₂ → 4NO + 6H₂O
  (i) Identify what is oxidised in stage 1.
  Give a reason for your answer.
  (ii) In this reaction the predicted yield of NO is 512g. The actual yield is 384g.
  Calculate the percentage yield of NO in this reaction.
  (iii) The equation for the reaction in stage 2 is shown.
  2NO + O₂ → 2NO₂
  Which major environmental problem does NO₂ cause if it is released into the atmosphere?
  (iv) The equation for the reaction in stage 3 is shown.
  4NO₂ + 2H₂O + O₂ → 4HNO₃
  Calculate the volume of O₂ gas, at room temperature and pressure (r.t.p.), needed to produce 1260g of HNO₃.
  Use the following steps.
  
• Calculate the number of moles of HNO₃.
  
• Deduce the number of moles of O₂ that reacted.
  
• Calculate the volume of O₂ gas that reacts at room temperature and pressure (r.t.p.).
  (e) The reaction in stage 3 is exothermic.
  4NO₂ + 2H₂O + O₂ → 4HNO₃
  Complete the energy level diagram for this reaction. Include an arrow that clearly shows the energy change during the reaction.

3. Chlorine is in Group VII of the Periodic Table.
   (a) Two isotopes of chlorine are chlorine-35 and chlorine-37.
   (i) State why these two isotopes of chlorine have the same chemical properties.
   (ii) Complete the table to show the number of electrons, neutrons and protons in each atom and ion.
   (b) (i) Chlorine reacts with aqueous sodium bromide.
   The equation for the reaction is shown.
   Cl₂ + 2NaBr → 2NaCl + Br₂
   State the type of reaction shown.
   (ii) Why is there no reaction between iodine and aqueous sodium bromide?
   (c) Magnesium reacts with chlorine to form magnesium chloride.
   Complete the dot-and-cross diagram to show the electron arrangement of the ions in magnesium chloride. Give the charges on the ions.
   The inner shells have been completed.
   (d) Hydrogen and chlorine react to form hydrogen chloride gas, as shown in the equation.
   H₂ + Cl₂ → 2HCl
   This equation can be represented as shown.
   H–H + Cl–Cl → 2H–Cl
   Some bond energies are shown in the table.
   Calculate the energy change for the reaction between hydrogen and chlorine, using the following steps.
   

• Calculate the energy needed to break the bonds.
• Calculate the energy released when bonds are formed.
• Calculate the energy change for the reaction.
  

4. (a) Filtration and chlorination are two stages in water treatment.
   State the purpose of each stage.
   (b) A student uses anhydrous copper(II) sulfate to test for the presence of water.
   (i) What colour change is seen if water is present?
   (ii) The purity of a sample of water can be assessed by measuring its boiling point.
   How is the boiling point of water affected by impurities?
   (c) Chromatography can be used to test the purity of substances.
   The diagram shows the chromatogram of a coloured substance.
   (i) How does this chromatogram show that this substance is not pure?
   (ii) Draw a circle round the correct Rf value for the spot labelled X.
   0.2 0.4 0.8 1.2
   (iii) State how a colourless substance can be made visible on a chromatogram.
   
5. (a) Complete the table about solids, liquids and gases.
   (b) The graph shows the change in temperature as a sample of a gas is cooled.
   Name the change of state taking place between A and B.
   (c) A bottle of liquid perfume is left open at the front of a room.
   After some time, the perfume is smelt at the back of the room.
   Name the two physical processes taking place.
   
6. (a) An endothermic reaction occurs when calcium nitrate is heated.
   (i) Balance the equation for this reaction.
   (ii) State the type of reaction shown by the equation.
   (b) Describe the test for a nitrate ion.
   
7. Aluminium is extracted by electrolysis. Iron is extracted from its ore by reduction with carbon.
   (a) What is meant by the term electrolysis?
   (b) Name the main ore of aluminium.
   (c) (i) Explain why aluminium cannot be extracted by reduction with carbon.
   (ii) Describe the role of cryolite in the extraction of aluminium by electrolysis.
   (iii) Name the product formed at the positive electrode.
   (iv) Write the ionic half-equation for the reaction at the negative electrode.
   (d) Aluminium is used in overhead electricity cables.
   Give two properties of aluminium that make it suitable for use in overhead electricity cables.
   (e) Iron is a transition element.
   (i) Iron forms hydrated iron(III) oxide when it rusts.
   Write a word equation to represent the formation of rust.
   (ii) Give two ways in which the properties of transition elements differ from the properties of Group I metals.
   
8. (a) Part of the synthetic polymer, nylon, is shown in the diagram.
   (i) Circle one amide linkage on the diagram.
   (ii) Complete the structures of the two monomers that react to form nylon.
   (iii) Name the other product formed when nylon is produced.
   (b) Items made from nylon are often disposed of by burying them in the ground. This is called landfill.
   Why is the disposal of nylon using landfill a problem?
   (c) Give the name of a natural polymer.

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