IGCSE Chemistry 2020 0620/42 Feb/Mar

IGCSE 2020 0620/42 Feb/Mar (pdf)

• Show Video with Step-by-Step Solutions for Q1 - Q2

• Show Video with Step-by-Step Solutions for Q3 - Q5

1. Petroleum is a useful natural resource.
   The diagram shows how petroleum can be separated into useful substances.
   (a) What is the name of the separation process shown in the diagram?
   (b) Name the fraction leaving at:
   A
   B
   (c) Refinery gas is a mixture of hydrocarbons.
   One refinery gas is butane, C₄H₁₀.
   (i) Suggest the names of two other refinery gases.
   (ii) Write the chemical equation for the complete combustion of butane.
   (iii) Name the toxic gas produced by the incomplete combustion of butane.
   (d) Gasoline and kerosene are both fuels. They have different properties.
   (i) Describe the differences in the properties given.
   (ii) What difference in the molecules of gasoline and kerosene causes these differences in properties?
   (e) Hydrogen fuel cells can be used to power vehicles.
   Write the word equation for the overall reaction that takes place in a hydrogen fuel cell.
   
2. Aluminium is extracted from its ore. The ore is converted into pure aluminium oxide, which then undergoes electrolysis as shown.
   (a) (i) Name an ore of aluminium.
   (ii) What is meant by the term electrolysis?
   (b) Aluminium oxide has a melting point of about 2000°C, but the electrolysis process operates at about 900°C.
   (i) Name the compound added to aluminium oxide to reduce the operating temperature.
   (ii) Suggest one benefit to the environment of reducing the operating temperature.
   (iii) Write the ionic half-equation for the reaction taking place at:
   the negative electrode (cathode)
   the positive electrode (anode)
   (iv) Explain why the anodes need frequent replacement.
   (c) Aluminium oxide reacts with acids and with alkalis.
   (i) What term is used to describe an oxide that reacts with acids and with alkalis?
   (ii) Aluminium oxide reacts with dilute sulfuric acid to form a salt.
   State the name and write the formula of the salt formed.
   (iii) Aluminium oxide reacts with dilute sodium hydroxide to form a salt and one other product. Name the other product.
   (iv) Aluminium hydroxide, Al(OH)₃, decomposes when heated to form aluminium oxide and water.
   Write the chemical equation for this reaction.
   (v) Suggest the names of two other aluminium compounds that decompose when heated to form aluminium oxide.

3. The Periodic Table is a method of classifying elements.
   (a) Identify the element which is in Group VI and Period 4.
   (b) Calcium is in Group II and chlorine is in Group VII of the Periodic Table.
   Explain, in terms of number of outer shell electrons and electron transfer, how calcium atoms and chlorine atoms form ions. Give the formulae of the ions formed.
   (c) Group V chlorides are covalent molecules. The boiling points of some Group V chlorides are shown.
   (i) Suggest the approximate boiling point of PCl₃.
   (ii) Explain the trend in boiling points in terms of attractive forces between particles.
   (iii) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of PCl₃.
   Show outer electrons only.
   (d) PCl₃ reacts with chlorine, Cl₂, to form PCl₅. This reaction is exothermic and reaches an equilibrium.
   PCl₃(g) + Cl₂(g) ⇄ PCl₅(g)
   (i) Describe two features of an equilibrium.
   (ii) State the effect, if any, on the position of this equilibrium when the following changes are made.
   Explain your answers.
   (iii) Explain, in terms of particles, what happens to the rate of the forward reaction when the reaction mixture is heated.
   (e) PCl₅ reacts with lithium fluoride, LiF, to form LiPF₆.
   PCl₅ + 6LiF → LiPF₆ + 5LiCl
   Calculate the mass of LiF needed to form 3.04g of LiPF₆ using the following steps.

• Calculate the number of moles of LiPF₆ formed.
  (Mr: LiPF6, 152)
• Deduce the number of moles of LiF needed.
• Calculate the mass of LiF needed.
  (f) Lithium fluoride has ionic bonding.
  (i) What is an ionic bond?
  (ii) Give two physical properties of ionic compounds.
  

4. Iron is a typical transition element.
   Iron:
   

• acts as a catalyst
• forms coloured compounds
• has more than one oxidation state.
  (a) Name one major industrial process that uses iron as a catalyst and name the product made in this process.
  (b) When aqueous sodium hydroxide is added to aqueous iron(II) sulfate, a precipitate forms.
  (i) What colour is this precipitate?
  (ii) Write the ionic equation for this reaction. Include state symbols.
  (c) Iron(II) sulfate can be converted to iron(III) sulfate by potassium manganate(VII) at room temperature.
  (i) What is the role of potassium manganate(VII) in this reaction?
  (ii) What condition must be used for this reaction to occur?
  (iii) In terms of electron transfer, what happens to the iron(II) ions in this reaction?
  (iv) State the colour change seen during this reaction.
  (d) Deduce the charge on the iron ion in each of these compounds.
  

5. There are two types of polymers.
   (a) Addition polymers are made from many identical small units.
   (i) What is the term used to describe these small units?
   (ii) A section of an addition polymer is shown.
   Draw the structure of the small unit used to make this addition polymer.
   Show all of the atoms and all of the bonds.
   (b) Polyamides are condensation polymers.
   What does the term condensation mean when used to describe this type of polymer?
   (c) A polyamide can be made from two different molecules.
   A simplified structure of octanedioic acid is shown.
   A simplified structure of 1,6-diaminohexane is shown.
   (i) Complete the diagram to show a section of polyamide manufactured from octanedioic acid and 1,6-diaminohexane. Include all of the atoms and all of the bonds in the linkages.
   (ii) State the name of a synthetic polyamide.

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