IGCSE Chemistry 2020 0620 Specimen paper 4

IGCSE 2020 0620 Specimen paper 4 (pdf)

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1. The following table gives information about six substances.
   (a) Which substance could be a metal?
   (b) State all the substances that are liquid at room temperature.
   (c) Which substance could have a macromolecular structure similar to that of silicon(IV) oxide?
   (d) Which substance could be propane?
   (e) Which substance could be sodium chloride?
   
2. The table gives the composition of three particles.
   (a) What is the evidence in the table for each of the following?
   (i) Particle A is an atom.
   (ii) A, B and C are all particles of the same element.
   (iii) Particles A and C are isotopes of the same element.
   (b) (i) What is the electronic structure of particle A?
   (ii) Is element A, a metal or a non-metal? Give a reason for your choice.
   
3. Kinetic theory explains the properties of matter in terms of the arrangement and movement of particles.
   (a) Nitrogen is a gas at room temperature. Nitrogen molecules, N₂, are spread far apart and move in a random manner at high speed.
   (i) Draw the electronic structure of a nitrogen molecule.
   Show only the outer electron shells.
   (ii) Compare the movement and arrangement of the molecules in solid nitrogen to those in nitrogen gas.
   (b) A sealed container contains nitrogen gas. The pressure of the gas is due to the molecules of the gas hitting the walls of the container.
   Use the kinetic theory to explain why the pressure inside the container increases when the temperature is increased.
   The following apparatus can be used to measure the rate of diffusion of a gas.
   The following results were obtained.
   (c) (i) Explain why nitrogen gas diffuses faster than chlorine gas.
   (ii) Explain why the nitrogen gas diffuses faster at the higher temperature.
   

4. Chromium is a transition element. (a) (i) State two differences in the physical properties of chromium and sodium.
   (ii) State two differences in the chemical properties of chromium and sodium.
   (b) Chromium is used to electroplate steel objects. The diagram shows how this could be done.
   (i) Give two reasons why steel objects are plated with chromium.
   (ii) The formula of the chromium(III) ion is Cr³⁺ and of the sulfate ion is SO₄^2–. Give theformula of chromium(III) sulfate.
   (iii) Write the ionic half-equation for the reaction at the negative electrode (cathode).
   (iv) A colourless gas, which relights a glowing splint, is formed at the positive electrode (anode).
   State the name of this gas.
   (v) During electroplating, it is necessary to add more chromium(III) sulfate but during copper plating using a copper anode, it is not necessary to add more copper(II) sulfate. Explain this difference.
5. Iron is extracted from its ore, hematite, in the blast furnace.
   Describe the reactions involved in this extraction.
   Include one equation for a redox reaction and one for an acid/base reaction.
   
6. Soluble salts can be made using a base and an acid.
   (a) Complete this method of preparing dry crystals of the soluble salt
   cobalt(II) chloride-6-water from the insoluble base cobalt(II) carbonate. step 1
   Add an excess of cobalt(II) carbonate to hot dilute hydrochloric acid.
   (b) (i) 5.95g of cobalt(II) carbonate were added to 40cm3 of hydrochloric acid, concentration 2.0mol/dm³
   Calculate the maximum yield of cobalt(II) chloride-6-water and show that the cobalt(II) carbonate was in excess.
   CoCO₃ + 2HCl → CoCl₂ + CO₂ + H₂O
   CoCl₂ + 6H₂O → CoCl₂.6H₂O
   (ii) Explain how these calculations show that cobalt(II) carbonate is in excess.
   
7. Iodine reacts with chlorine to form dark brown iodine monochloride.
   I₂ + Cl₂ → 2ICl
   This reacts with more chlorine to give yellow iodine trichloride.
   An equilibrium forms between these iodine chlorides.
   ICl(l) + Cl₂(g) ⇄ ICl₃(s)
   (a) What do you understand by the term equilibrium?
   (b) When the equilibrium mixture is heated, it becomes a darker brown colour.
   Suggest if the reverse reaction is endothermic or exothermic. Give a reason for your choice.
   (c) The pressure on the equilibrium mixture is decreased.
   (i) How would this affect the position of equilibrium? Give a reason for your choice.
   (ii) Describe what you would observe.
   (d) Calculate the overall energy change for the reaction between iodine and chlorine using the bond energy values shown.
   (e) Draw a labelled energy level diagram for the reaction between iodine and chlorine using the information in (d).
   
8. The alcohols form an homologous series.
   (a) Give three characteristics of an homologous series.
   (b) The following two alcohols are members of an homologous series and they are isomers.
   (i) Explain why they are isomers.
   (ii) Deduce the structural formula of another alcohol which is also an isomer of these alcohols.
   (c) Copper(II) oxide can oxidise butanol to liquid X, whose pH is 4.
   (i) Give the name of another reagent which can oxidise butanol.
   (ii) Which homologous series does liquid X belong to?
   (iii) State the formula of liquid X.
   (d) The alcohol ethanol can be made by fermentation. Yeast is added to aqueous glucose. C₆H₁₂O₆(aq) → 2C₂H₅OH(aq) + 2CO₅(g)
   Carbon dioxide is given off and the mixture becomes warm, as the reaction is exothermic.
   The graph shows how the rate of reaction varies over several days.
   (i) Suggest a method of measuring the rate of this reaction.
   (ii) Why does the rate initially increase?
   (iii) Suggest two reasons why the rate eventually decreases.
   
9. There are two types of polymerisation, addition and condensation.
   (a) Explain the difference between these two types of polymerisation.
   (b) Some plastics, formed by polymerisation, are non-biodegradable.
   Describe two pollution problems that are caused by non-biodegradable plastics.
   (c) The polymer known as PVA is used in paints and adhesives. Its structural formula is shown below.
   Deduce the structural formula of its monomer.
   (d) A condensation polymer can be made from the following monomers.
   HOOC(CH₂)₄COOH and H₂N(CH₂)₆NH₂
   Draw the structural formula of this polymer.
   

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