CAIE A Level 9701

Chemistry 2020 · Oct/Nov

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This CAIE A Level Chemistry paper focuses strongly on inorganic chemistry, especially Period 3 trends, oxides and their acid–base behaviour, lattice structures, and reactions of common compounds such as phosphorus chlorides, aluminium oxide, silicon(IV) oxide, and sodium carbonate. It also includes organic chemistry, with questions on reaction types, structural isomerism, optical isomerism, reagents and conditions, and identification of products, as well as a calculation-based question on pressure and decomposition.…

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Questions & Model Answers 34 Qs

Q1
Short Answer 1 mark
Represent the ions 1H+, 2H+ and 3H+. State, in terms of subatomic particles in the nucleus, what is the same about each of these ions and what is different.
Same: each ion has 1 proton in the nucleus.
All hydrogen ions are isotopes of hydrogen and therefore each nucleus contains one proton.
Different: they have different numbers of neutrons.
1H+ has 0 neutrons, 2H+ has 1 neutron and 3H+ has 2 neutrons.
Q2a
Short Answer 1 mark
State the trend in acid/base behaviour of the oxides of the Period 3 elements, from Na to S.
The oxides change from basic to amphoteric to acidic across Period 3.
Metal oxides are basic, aluminium oxide is amphoteric, and non-metal oxides are acidic.
Q2b
Short Answer 2 marks
State and explain the trend, from Na to S, in the maximum oxidation number of the Period 3 elements in their oxides.
The maximum oxidation number increases from +1 to +6 across the period.
The number of outer-shell electrons increases from Na to S, so the highest oxidation state in oxides increases.
Q2c
Short Answer 2 marks
Sodium oxide and phosphorus(V) oxide both react with water. Name the product of each reaction.
Sodium hydroxide
Na2O + H2O forms NaOH.
Phosphoric(V) acid
P4O10 / P2O5 reacts with water to form H3PO4.
Q2d
Short Answer 3 marks
Explain why phosphorus(V) oxide has a low melting point of approximately 300 °C but magnesium oxide has a high melting point of approximately 2850 °C.
Phosphorus(V) oxide is a simple molecular substance with weak intermolecular forces between molecules, so little energy is needed to melt it.
Magnesium oxide has a giant ionic lattice with strong electrostatic attractions between Mg2+ and O2− ions.
A large amount of energy is needed to overcome these strong ionic bonds, so MgO has a much higher melting point.
Q2e(i)
Short Answer 1 mark
Write an equation for the reaction of aluminium oxide with excess aqueous hydrochloric acid.
Al2O3 + 6HCl → 2AlCl3 + 3H2O
Q2e(ii)
Short Answer 1 mark
Write an equation for the reaction of aluminium oxide with excess aqueous sodium hydroxide.
Al2O3 + 2NaOH + 3H2O → 2Na[Al(OH)4]
Q2f
Short Answer 2 marks
Describe the lattice structure of silicon(IV) oxide. Your answer should include reference to the arrangement of the silicon and oxygen atoms and the bonds between them.
A giant covalent lattice with each silicon atom covalently bonded to four oxygen atoms and each oxygen atom covalently bonded to two silicon atoms.
Q2g(i)
Short Answer 1 mark
Write an equation for the reaction of sodium oxide with silicon(IV) oxide to form sodium silicate(IV), Na2SiO3.
Na2O + SiO2 → Na2SiO3
Q2g(ii)
Short Answer 1 mark
Write an equation for the thermal decomposition of sodium carbonate, forming sodium oxide and carbon dioxide.
Na2CO3 → Na2O + CO2
Q3a(i)
Short Answer 1 mark
Write an equation for the formation of PCl5 from the reaction of phosphorus and chlorine.
P4 + 10Cl2 → 4PCl5
Q3a(ii)
Short Answer 1 mark
State the type of structure and bonding shown by liquid PCl5.
Simple molecular structure with covalent bonding.
Q3b(i)
Short Answer 1 mark
Give one other observation you would make when PCl5 reacts with excess water.
Steamy fumes / white mist / vigorous effervescence may be observed.
Q3b(ii)
Short Answer 1 mark
Write the equation for the reaction of PCl5 with excess water.
PCl5 + 4H2O → H3PO4 + 5HCl
Q3b(iii)
Short Answer 1 mark
Estimate the pH of the resulting solution.
About 1
Q3c(i)
Short Answer 1 mark
Identify a reagent that could be used in reaction 1.
PCl3
Q3c(ii)
Short Answer 2 marks
Explain what is meant by the term optical isomer and circle any atom(s) in T that give rise to optical isomerism.
Optical isomers are non-superimposable mirror images.
They arise from carbon atoms bonded to four different groups.
Q3c(iii)
Short Answer 1 mark
T is a minor product in the reaction of compound S with excess HCl. Draw the structure of the major product of the reaction of S with excess HCl.
The major product is the fully substituted chloroalkane formed by replacing all hydroxyl groups in S with chlorine atoms.
Q3d(i)
Short Answer 2 marks
Predict the shape of the NCl3 molecule and the Cl-N-Cl bond angle.
Trigonal pyramidal
About 107°
Q3d(ii)
Short Answer 2 marks
Explain fully what is meant by the term weak Brønsted-Lowry acid.
A Brønsted-Lowry acid is a proton donor.
A weak acid only partially dissociates / ionises in water.
Q3d(iii)
Short Answer 4 marks
Calculate the final total pressure inside the sealed container at 20 °C after the NCl3(l) has fully decomposed.
Final total pressure = 1.24 × 10^5 Pa
Q4a(i)
Short Answer 1 mark
State the type of reaction that occurs in reaction 1.
Reduction
Q4a(ii)
Short Answer 2 marks
Suggest the reagent(s) and conditions required for reaction 1.
NaBH4 in aqueous solution, at room temperature.
Q4a(iii)
Short Answer 1 mark
Draw the structure of the organic product, H, from reaction 2.
The product is the carboxylic acid formed by oxidation of the aldehyde group to COOH.
Q4a(iv)
Short Answer 1 mark
State what you would observe in reaction 3.
A silver mirror forms / a grey silver precipitate is produced.
Q4a(v)
Short Answer 1 mark
Give the type of reaction shown by reaction 4.
Esterification
Q4b(i)
Short Answer 1 mark
Name the type of structural isomerism shown by G and J.
Functional group isomerism
Q4b(ii)
Short Answer 2 marks
Suggest one chemical test that can distinguish G from J. Give the result of the test with each compound.
Use aqueous bromine.
G decolourises bromine water; J does not react / no change.
Q4b(iii)
Short Answer 1 mark
State the role of NaBH4 in the reactions with G and J.
Reducing agent
Q4b(iv)
Short Answer 1 mark
Identify the organic product K.
The alcohol formed by reduction of the carbonyl group in G and J.
Q4c
Short Answer 3 marks
Complete the table with the expected observations for the reactions of P and Q with the named reagents.
Br2(aq): P decolourises bromine water; Q no change.
2,4-dinitrophenylhydrazine: P orange precipitate; Q orange precipitate.
Aqueous sodium carbonate: P effervescence / CO2 produced; Q no reaction.
Q4d(i)
Short Answer 1 mark
Identify the bonds responsible for the absorptions marked X and Z.
X: C=O
Z: O–H
Q4d(ii)
Short Answer 1 mark
Name M.
Hexanedioic acid
Q4d(iii)
Short Answer 1 mark
Use the information in (d) to deduce the molecular formula of L.
C10H18O4
Paper Details
Board CAIE
Level A Level
Subject Chemistry
Code 9701
Year 2020
Session Oct/Nov
Q&A 34 questions
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