IGCSE Chemistry 2020 0620/41 May/June
Cambridge CIE IGCSE Chemistry Past Papers and solutions.
Questions and Worked Solutions for IGCSE 2020 0620/41 May/June Paper 4 (Extended).
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IGCSE 2020 0620/41 May/June (pdf)
- This question is about elements X, Y and Z.
(a) An atom of element X is represented as 3416X.
(i) Name the different types of particles found in the nucleus of this atom of X.
(ii) What is the term for the total number of particles in the nucleus of an atom?
(iii) What is the total number of particles in the nucleus of an atom of 3416X ?
(iv) What is the electronic structure of the ion X2– ?
(v) Suggest the formula of the compound formed between aluminium and X.
(b) (i) What term is used to describe atoms of the same element with different numbers of particles in the nucleus?
(ii) Identify the atom against which the relative masses of all other atoms are compared.
(iii) What is the name of the amount of any substance that contains 6.02 × 1023 particles?
(iv) The constant 6.02 × 1023 has a name.
What is the name of this constant?
(c) Part of the definition of relative atomic mass is ‘the average mass of naturally occurring atoms of an element’.
Some relative atomic masses are not whole numbers.
Element Y has only two different types of atom, 69Y and 71Y.
The ratio of atoms present in element Y is shown.
69Y: 71Y = 3:2
- Calculate the relative atomic mass of element Y to one decimal place.
- Identify element Y.
(d) Element Z is in Period 3 and Group V.
(i) Identify element Z.
(ii) Explain in terms of electron transfer why Z behaves chemically as a non-metal.
- Magnesium is a metal.
(a) Name and describe the bonding in magnesium.
(b) Magnesium oxide, MgO, is formed when magnesium burns in oxygen.
(i) Complete the dot-and-cross diagram to show the electron arrangement of the ions in magnesium oxide.
The inner shells have been drawn.
Give the charges on the ions.
(ii) Write the chemical equation for the reaction that occurs when magnesium burns in oxygen.
(c) Magnesium oxide also forms when magnesium nitrate, Mg(NO3)2, is heated strongly. This is an endothermic reaction.
(i) Write the chemical equation for this reaction.
(ii) What type of reaction is this?
(iii) Name two other compounds of magnesium that form magnesium oxide when heated.
- Sulfur dioxide, SO2, is used in the manufacture of sulfuric acid.
(a) In the first stage of the process, sulfur dioxide is obtained from sulfur-containing ores. Name one of these ores.
(b) The next stage of the process is a reaction which can reach equilibrium.
The equation for this stage is shown.
2SO2(g) + O2(g) ⇄ 2SO3(g)
(i) Describe two features of an equilibrium.
(ii) Name the catalyst used in this stage.
(iii) Why is a catalyst used?
(iv) Explain, in terms of particles, why a high temperature increases the rate of this reaction.
(v) In this stage, only a moderate temperature of 450°C is used.
What does this suggest about the forward reaction?
(vi) Calculate the percentage by mass of sulfur in sulfur trioxide, SO3.
(c) Concentrated sulfuric acid is a dehydrating agent which can chemically remove water from substances.
Both hydrated copper(II) sulfate crystals and sucrose (a sugar), C12H22O11, can be completely
dehydrated by concentrated sulfuric acid.
Name the solid product formed in each case.
(d) When propan-1-ol is heated with concentrated sulfuric acid as a catalyst an unsaturated hydrocarbon of relative molecular mass 42 is formed and one other product.
(i) What is meant by the term unsaturated?
(ii) Write the chemical equation for this reaction.
(iii) Name the unsaturated hydrocarbon formed. - This question is about reactions of bases and acids.
(a) Ammonia is a gas at room temperature.
What is the test for ammonia gas? Describe the positive result of this test.
(b) Ammonia reacts with water to form ions.
NH3 + H2O ⇄ NH4+ + OH-
(i) How does this equation show that ammonia, NH3, behaves as a base?(ii) Aqueous ammonia is described as a weak base.
Suggest the pH of aqueous ammonia.
(iii) Describe what is seen when aqueous ammonia is added to aqueous copper(II) sulfate, until no further change is seen.
(c) Aqueous sodium hydroxide, NaOH(aq), is a strong alkali that reacts with dilute sulfuric acid exothermically.
(i) What type of reaction is this?
(ii) Complete the equation for the reaction between aqueous sodium hydroxide and dilute sulfuric acid.
(d) A student wanted to find the concentration of some dilute sulfuric acid by titration. The student found that 25.0cm3 of 0.0400mol/dm3 NaOH(aq) reacted exactly with 20.0cm3 of H2SO4(aq).
(i) Name a suitable indicator to use in this titration.
(ii) Calculate the concentration of the H2SO4(aq) in mol/dm3 using the following steps.
- Calculate the number of moles of NaOH in 25.0cm3.
- Deduce the number of moles of H2SO4 that reacted with the 25.0cm3 of NaOH(aq).
- Calculate the concentration of H2SO4(aq) in mol/dm3.
(iii) Calculate the concentration of the 0.0400mol/dm3 NaOH(aq) in g/dm3.
- Ethanol is manufactured by two different processes.
(a) For each process, name the organic reactant and state the type of reaction.
(b) Alcohols can be oxidised to form carboxylic acids.
Name a suitable oxidising agent for this reaction.
(c) Alcohols can be partially oxidised to form aldehydes.
Aldehydes are a homologous series of organic compounds.
Partial oxidation is achieved by reacting an alcohol with the oxidising agent in distillation apparatus as shown.
(i) Name apparatus A.
(ii) On the diagram, use one arrow to show where water enters apparatus A.
(d) The table shows some information about aldehydes.
(i) Complete the table.
(ii) Deduce the general formula of aldehydes.
(e) The structural formula of ethanal is shown.
The C=O group in aldehydes is at the end of the carbon chain.
This is a reactive part of the molecule.
(i) What is the name given to the reactive part of any organic molecule?
(ii) Complete the dot-and-cross diagram to show the electron arrangement of a molecule of ethanal. Inner shells have been drawn.
(f) Propanone belongs to a homologous series called ketones. Ketones have the same C=O group as aldehydes but the C=O group is not at the end of the carbon chain. Propanone has the same molecular formula as propanal, C3H6O.
(i) What term is used to describe molecules with different structures but with the same molecular formula?
(ii) Suggest the structure of propanone, C3H6O. Show all of the atoms and all of the bonds.
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