Aldehydes and Ketones: Nucleophilic Addition and the Tests That Separate Them · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Aldehydes, ketones and their tests

Science · Chemistry · ages 17-18
Name ______________________   Date ____________

  1. What does Tollens reagent do to an aldehyde and to a ketone?

    • Mirrors both of them
    • Mirrors neither of them
    • Mirrors aldehydes only

  2. Why does a nucleophile attack the carbonyl carbon?

    • It carries a partial positive charge
    • The carbon carries a full negative charge
    • The oxygen pushes nucleophiles onto carbon

  3. Fehling solution stays blue with ketones but turns brick red with aldehydes.

    Circle one:   True   False

  4. Propanal reacts with cyanide. Why do equal amounts of both mirror forms appear?

    • Both faces are equally open
    • The cyanide used is already a mixture
    • The product keeps flipping between forms

  5. What happens to the carbonyl double bond when cyanide adds?

    • It stays exactly as it was
    • It breaks; CN bonds to carbon
    • It moves onto the oxygen alone

  6. What does reduction give for propanal and for propanone?

    • Primary alcohol from propanal, secondary alcohol from propanone
    • Secondary alcohol from propanal, primary alcohol from propanone
    • A carboxylic acid from both of them

  7. A student draws only one mirror form from cyanide addition to propanal and calls it complete. What is missing?

    • Its twin from the other face
    • A second cyanide adding to the same carbon
    • The water molecule that splits the product

  8. An unknown gives no mirror with Tollens but reddens Fehling. A student calls it a ketone. What is wrong?

    • Nothing is wrong, since ketones redden Fehling
    • Fehling says aldehyde; repeat Tollens
    • Both tests always agree, so the sample must be water
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Aldehydes, ketones and their tests W1-mt_bVcJ0UaXk6-s1

  1. Mirrors aldehydes only · Aldehydes oxidise further and plate the mirror, while ketones resist.
  2. It carries a partial positive charge · Oxygen drags electrons away, leaving carbon short of charge and inviting attack.
  3. True · Only aldehydes reduce the blue mixture to red solid. The sentence is true.
  4. Both faces are equally open · The flat carbonyl of propanal shows two equal faces, and its new carbon holds four different groups, so both attacks give mirror forms equally often.
  5. It breaks; CN bonds to carbon · The double bond opens so CN can bond to carbon and oxygen becomes OH.
  6. Primary alcohol from propanal, secondary alcohol from propanone · Aldehydes reduce to primary alcohols and ketones to secondary alcohols.
  7. Its twin from the other face · Both faces react equally, so with propanal the product is always the pair, never one alone.
  8. Fehling says aldehyde; repeat Tollens · Brick red with Fehling means an aldehyde, which should also mirror, so the Tollens run went wrong.
Worksheet · LightMySky