CAIE
A Level
9701
Chemistry 2020 · May/June
18 Questions
Q&A Available
Questions & Model Answers 18 Qs
Q1c(i)
Short Answer
1 mark
for the activation energy of reaction A.
Activation energy of reaction A = the energy difference between the reactants and the peak of the energy profile for reaction A.
Activation energy is the minimum energy needed for reaction to occur.
Q1c(ii)
Short Answer
1 mark
The enthalpy change for reaction A is -14 kJ mol-1. Predict a value for the enthalpy change for reaction B.
A suitable predicted value is +14 kJ mol-1.
Reaction B is the reverse of reaction A, so the enthalpy change has the same magnitude but opposite sign.
Q1c(iii)
Structured
2 marks
Sketch a labelled energy level diagram for reaction B. Use relevant values from (c)(i) and (c)(ii).
Energy level diagram with reactants and products labelled, a peak showing the activation energy for reaction B, and an overall enthalpy change of +14 kJ mol-1.
Reaction B is endothermic, so products are higher in energy than reactants by 14 kJ mol-1.
Q1d(i)
Short Answer
2 marks
Explain what is meant by the term enthalpy change of combustion of sucrose.
The enthalpy change when 1 mol of sucrose is completely burned in excess oxygen under standard conditions, with all reactants and products in their standard states.
This is the standard definition of enthalpy change of combustion.
Q1d(ii)
Structured
3 marks
Use the Data Booklet to calculate the enthalpy change, in kJ mol-1, for the combustion of sucrose. Assume that all of the heat energy produced is transferred to the water. Show your working.
q = mcΔT = 250 × 4.18 × (40.7 - 25.0) = 1.64 × 10^4 J = 16.4 kJ
Molar mass of sucrose, C12H22O11 = 342 g mol-1
Moles of sucrose = 1.00 / 342 = 2.92 × 10^-3 mol
ΔHc = -16.4 / (2.92 × 10^-3) = -5.62 × 10^3 kJ mol-1
The heat gained by water equals heat released by combustion; the negative sign shows combustion is exothermic.
Q4a(i)
Short Answer
1 mark
Suggest the identity of X.
X is chlorine.
A cream precipitate with silver nitrate indicates AgCl.
Q4a(ii)
Short Answer
1 mark
Write an ionic equation to describe the formation of the cream precipitate. Include state symbols.
Ag+(aq) + Cl-(aq) -> AgCl(s)
Silver ions react with chloride ions to form cream silver chloride precipitate.
Q4a(iii)
Short Answer
2 marks
Describe a further test which would confirm the identity of X. test expected result
Test the precipitate with dilute aqueous ammonia; silver chloride dissolves in dilute ammonia to give a colourless solution.
AgCl is soluble in dilute ammonia, unlike AgBr and AgI.
Q4b(i)
Short Answer
1 mark
Suggest the structural formula of the straight-chain halogenoalkane Q.
CH3CH2CH2CH2CH2Cl
A straight-chain C5H11Cl halogenoalkane that undergoes SN2 is 1-chloropentane.
Q4b(ii)
Short Answer
2 marks
Explain why the reaction tends to proceed via an SN2 mechanism rather than an SN1 mechanism.
Because Q is a primary halogenoalkane, formation of a primary carbocation is unstable and unlikely, so substitution occurs in one step by nucleophilic attack and leaving group departure (SN2).
Primary halogenoalkanes favour SN2 due to poor carbocation stability.
Q4c(i)
Short Answer
1 mark
Name the type of reaction occurring.
Elimination.
Alcoholic hydroxide and heat under reflux promote elimination of HCl from halogenoalkanes.
Q4c(ii)
Short Answer
1 mark
Write an equation, using molecular formulae, to represent the reaction occurring.
C4H9Cl + NaOH -> C4H8 + NaCl + H2O
Elimination of HCl from C4H9Cl gives methylpropene, molecular formula C4H8.
Q4c(iii)
Short Answer
1 mark
Draw the skeletal formula of methylpropene.
2-methylpropene, skeletal formula: CH2=C(CH3)2
Methylpropene is 2-methylpropene.
Q4c(iv)
Short Answer
2 marks
Give the names of P and R.
P and R are 1-chlorobutane and 2-chlorobutane.
Both isomers can eliminate to form methylpropene as the major product.
Q5a
Structured
6 marks
Complete the table to give the name of the reaction mechanisms of reactions 1 and 6 and the reagents and conditions required for reactions 1, 2 and 6.
Reaction 1 mechanism: electrophilic addition; reagent/conditions: HBr(g) or hydrogen bromide, room temperature.
Reaction 2 reagent/conditions: steam, phosphoric acid catalyst, high temperature and pressure.
Reaction 6 mechanism: nucleophilic substitution; reagent/conditions: aqueous NaOH, heat under reflux.
Ethene commonly undergoes electrophilic addition with hydrogen halides, hydration with steam, and haloalkane hydrolysis by nucleophilic substitution.
Q5b(i)
Structured
3 marks
In reaction 3 the organic molecule reacts with HCN and a KCN catalyst. Complete the diagram to show the mechanism of the reaction occurring. Include all relevant dipoles, lone pairs and curly arrows in your answer.
Mechanism: CN- attacks the δ+ carbon of the carbonyl group; the C=O pi bond moves to oxygen to form an alkoxide intermediate; then the alkoxide is protonated by HCN to form the hydroxynitrile.
This is nucleophilic addition to a carbonyl compound.
Q5b(ii)
Short Answer
2 marks
Name the functional groups present in the product of reaction 3.
Hydroxyl (alcohol) and nitrile.
HCN addition to a carbonyl gives a hydroxynitrile containing both groups.
Q5c
Short Answer
1 mark
Draw the structure of the organic molecule W formed in reaction 4.
W is the alcohol formed by reduction of the carbonyl compound in reaction 4; structure: CH3CH(OH)CH3 if the starting carbonyl is propanone, or the corresponding reduced alcohol shown by the reaction scheme.
Reaction 4 is reduction of a carbonyl compound to an alcohol.
Paper Details
| Board | CAIE |
| Level | A Level |
| Subject | Chemistry |
| Code | 9701 |
| Year | 2020 |
| Session | May/June |
| Q&A | 18 questions |
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