Edexcel International A Level Chemistry
Edexcel International A Level Chemistry Organic Synthesis Exam Questions
Free Edexcel International A Level Chemistry exam questions for Organic Synthesis, with a mark scheme for every pack. Covers multi-step synthesis routes, functional group conversions, extending carbon chains, Grignard reagents, practical techniques, hazards and choosing reaction conditions.
Organic Synthesis exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel International A Level Chemistry Organic Synthesis
Organic synthesis in Unit 5 of Edexcel International A Level Chemistry brings together all the organic reactions from Units 1 to 5. You plan routes of up to several steps to convert one compound into another, giving reagents and conditions at each stage, and you consider how to increase or reduce chain length using nitriles and Grignard reagents. Practical skills are central: heating under reflux, distillation, recrystallisation, melting temperature determination and separating liquids. You also weigh up yield, hazards and atom economy. Examiners often set unfamiliar target molecules, so knowing a clear map of functional group conversions is the best preparation.
What you need to know
- Functional group map Build a map linking alkanes, alkenes, halogenoalkanes, alcohols, aldehydes, ketones, carboxylic acids, esters, acyl chlorides, nitriles, amines and amides, with the reagents and conditions for each arrow.
- Increasing chain length Reaction of a halogenoalkane with KCN adds one carbon as a nitrile, which can be hydrolysed to an acid or reduced to an amine. Grignard reagents, RMgX made from a halogenoalkane and magnesium in dry ether, add an R group to a carbonyl compound or CO2.
- Grignard products Grignard reagents react with methanal to give primary alcohols, other aldehydes to give secondary alcohols, ketones to give tertiary alcohols and carbon dioxide to give carboxylic acids, after acid hydrolysis.
- Practical techniques Reflux for slow reactions with volatile liquids, distillation to separate and purify liquids, a separating funnel for immiscible layers, and recrystallisation from minimum hot solvent for solids. Melting temperature checks purity.
- Planning a route Work backwards from the target to identify the functional group needed, check the carbon count, and give each intermediate's name or structure with reagents and conditions.
- Yield and safety Overall yield is the product of the yields of each step. Consider hazards of reagents, such as using a fume cupboard for toxic HCN or KCN and dry conditions for LiAlH4 and Grignard reagents.
Common mistakes in Organic Synthesis
- Giving a reagent without conditions, for example 'KCN' rather than 'KCN in ethanol, heat under reflux'.
- Changing the carbon chain length without realising it. Count the carbons in the starting material and the target.
- Adding overall yields instead of multiplying them for a multi-step route.
- Describing recrystallisation with a large volume of cold solvent. Use the minimum volume of hot solvent, cool to crystallise, filter under reduced pressure and wash with cold solvent.
- Forgetting that Grignard reagents and LiAlH4 must be kept away from water.
Try three Organic Synthesis exam-style questions
1. Outline a two-step synthesis of propanoic acid from bromoethane, giving reagents, conditions and the intermediate. (4 marks)
Show the mark scheme answer
Step 1: KCN in ethanol, heat under reflux; intermediate propanenitrile, CH3CH2CN; step 2: dilute hydrochloric acid, heat under reflux; gives CH3CH2COOH.
2. A two-step synthesis has yields of 80% and 65%. Calculate the overall percentage yield. (1 mark)
Show the mark scheme answer
0.80 x 0.65 x 100 = 52%.
3. Describe how impure benzoic acid could be purified by recrystallisation and how its purity could be checked. (4 marks)
Show the mark scheme answer
Dissolve in the minimum volume of hot water (solvent); filter hot to remove insoluble impurities; cool so crystals form, then filter under reduced pressure and wash with a little cold solvent and dry; measure melting temperature, a sharp value matching the data book value shows purity.
Organic Synthesis FAQs
What does Edexcel International A Level Chemistry Organic synthesis cover?
It covers planning multi-step routes between functional groups, changing chain length with nitriles and Grignard reagents, practical preparation and purification techniques, yields and hazards.
Which unit is Organic synthesis examined in?
Organic synthesis is part of Unit 5, but it draws on organic reactions from Units 1, 2 and 4.
How do I revise for synthesis questions?
Make a one-page reaction map with every reagent and condition, test yourself by covering the arrows, and practise working backwards from unfamiliar target molecules.
