Lesson 17B.1

17B.1 Aldehydes and ketones: identification and reactions Quiz: Pearson Edexcel Chemistry, Unit 17

20 questions

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Lesson 17B.1, Aldehydes and ketones: identification and reactions: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 17: Organic Chemistry II, written with Revision Ninja.

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The 20 questions

  1. Which functional group identifies an aldehyde?

    • -CHO, a carbonyl group bonded to a hydrogen atom
    • -CO-, a carbonyl group bonded to two carbon atoms
    • -OH, a hydroxyl group bonded to a benzene ring
    • -COOH, a carbonyl group bonded to a hydroxyl group

  2. Why do aldehydes and ketones have lower boiling temperatures than alcohols of similar molar mass?

    • They are always gases at room temperature
    • They have a higher number of carbon atoms per molecule
    • They have stronger covalent bonds than alcohols
    • They cannot form intermolecular hydrogen bonds with each other

  3. Which reagent gives a silver mirror with an aldehyde but not with a ketone?

    • Iodine in alkali
    • Lithium tetrahydridoaluminate
    • Tollens' reagent
    • Acidified dichromate(VI) ions

  4. What is observed when an aldehyde is warmed with Fehling's solution?

    • A yellow precipitate of triiodomethane forms immediately
    • A white precipitate forms that dissolves in excess acid
    • The solution turns from blue to green with no solid forming
    • A brick-red precipitate forms as the blue copper(II) ions are reduced

  5. What is the product when propanal is reduced by lithium tetrahydridoaluminate in dry ether?

    • Propan-1-ol, a primary alcohol
    • Propanoic acid, a carboxylic acid
    • Propan-2-ol, a secondary alcohol
    • Propan-1-amine, a primary amine

  6. What is the product when propanone is reduced by lithium tetrahydridoaluminate?

    • Propan-2-ol, a secondary alcohol
    • Propanoic acid, a carboxylic acid
    • Propanal, an aldehyde
    • Propan-1-ol, a primary alcohol

  7. What is observed when propanone is warmed with alkaline iodine?

    • The solution turns from orange to green
    • A yellow precipitate of triiodomethane forms
    • A brick-red precipitate of copper(I) oxide forms
    • A silver mirror forms on the inside of the tube

  8. Which reagent is used to test for the presence of a carbonyl group in an unknown compound?

    • 2,4-dinitrophenylhydrazine (2,4-DNPH)
    • Fehling's solution, which forms a brick-red precipitate with reducing agents
    • Tollens' reagent, which forms a silver mirror with aldehydes
    • Lithium tetrahydridoaluminate in dry ether solution

  9. What is produced when an aldehyde is oxidised by acidified dichromate(VI) ions?

    • A ketone, with a brick-red precipitate forming
    • A primary alcohol, with the orange solution turning green
    • An alkene, with the orange solution decolourising
    • A carboxylic acid, with the orange solution turning green

  10. Ketones such as propanone do not react with Tollens' reagent. Why?

    • They form a stable complex with silver that is colourless
    • They are too volatile and evaporate before the reaction can start
    • They are reduced by silver ions to primary alcohols
    • They cannot be oxidised further without breaking carbon-carbon bonds

  11. A nucleophilic addition of HCN to propanone produces a product with a chiral centre. What is the result of the reaction?

    • A single enantiomer, since the reaction is stereospecific and always gives one form of the product
    • A racemic mixture, since the cyanide ion can attack either face of the planar carbonyl group
    • A product with no chiral centre, since the planar carbonyl carbon becomes achiral after the addition step
    • A pure alkene, since the carbonyl group is eliminated as water and the double bond is formed in the product

  12. Which reagent reduces an aldehyde to a primary alcohol?

    • Hydrogen gas with aqueous sodium hydroxide
    • Acidified dichromate(VI) ions with heating
    • Lithium tetrahydridoaluminate in dry ether
    • Fehling's solution at room temperature

  13. Why is 2,4-DNPH used to identify a carbonyl compound once it has been detected?

    • It oxidises the carbonyl compound to an acid that can be titrated
    • The melting temperature of the orange precipitate is compared with data for known derivatives
    • It converts the carbonyl compound into an alkene that can be identified by bromine water
    • It reacts with the carbonyl group to form a colourless solution with a sharp smell

  14. Which statement about the reactions of aldehydes with Fehling's solution is correct?

    • Ketones reduce the copper(II) complex in Fehling's solution more readily than aldehydes do under the same conditions
    • Fehling's solution oxidises ketones to alkenes, which then decolourise the blue solution at room temperature
    • Both aldehydes and ketones give a silver mirror with Fehling's solution, which is a test for each functional group
    • Aldehydes reduce the copper(II) complex in Fehling's solution, and ketones do not give this reaction

  15. Which compound gives a positive iodoform test?

    • Propan-1-ol
    • Ethanoic acid
    • Ethanal
    • Methanol

  16. What is the mechanism type for the reaction of HCN with an aldehyde in the presence of KCN?

    • Nucleophilic addition, where the cyanide ion attacks the electron-deficient carbonyl carbon
    • Electrophilic addition, where the carbonyl oxygen attacks the cyanide ion
    • Elimination, where water is removed to form a carbon-carbon double bond
    • Free-radical substitution, where a hydrogen atom is replaced by CN

  17. In the reaction of an aldehyde with lithium tetrahydridoaluminate, what does [H] represent in the equation?

    • The reducing agent, which supplies hydrogen atoms in the reduction
    • The oxidising agent that removes hydrogen from the aldehyde
    • The acid catalyst that protonates the carbonyl oxygen
    • The solvent that dissolves the organic product

  18. What is observed when a ketone such as propanone is warmed with Tollens' reagent?

    • The solution turns green as the reagent is oxidised
    • No silver mirror forms, and the reagent stays unchanged
    • A brick-red precipitate forms in the solution
    • A silver mirror forms on the inside of the tube

  19. What is the product of the reaction of propanone with 2,4-DNPH?

    • A yellow or orange solid derivative, the 2,4-dinitrophenylhydrazone
    • A brick-red precipitate of copper(I) oxide formed in the solution
    • A colourless gas that turns limewater milky when it is bubbled in
    • A silver mirror deposited on the walls of the tube by reduction

  20. What is the product when propanal is oxidised by acidified dichromate(VI) ions?

    • Propan-1-ol
    • Propanone
    • Propanoic acid
    • Propanoyl chloride

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