Aldehyde and Ketone Identification Quiz
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Questions and Answers

What is the general formula for ketones?

  • RCHO
  • RCOOR'
  • RCOR' (correct)
  • R(OH)R'
  • Which reagent is used to differentiate between aldehydes and ketones based on oxidation potential?

  • Tollen's reagent (correct)
  • 2,4-Dinitrophenylhydrazine
  • Benedict's solution
  • Chromic acid
  • What type of precipitate do aldehydes and ketones form when reacted with 2,4-Dinitrophenylhydrazine?

  • White
  • Colorless
  • Yellow or orange (correct)
  • Brown
  • What result indicates the presence of an aldehyde during Tollen's test?

    <p>Formation of a silver mirror</p> Signup and view all the answers

    How do aldehydes differ from ketones in their chemical reactivity?

    <p>Aldehydes can be easily oxidized whereas ketones cannot.</p> Signup and view all the answers

    What is the purpose of ammonium hydroxide in Tollen's reagent?

    <p>To prevent the formation of brown silver oxide</p> Signup and view all the answers

    Which of the following statements about formaldehyde is true?

    <p>Formaldehyde contains one hydrogen atom as the R group.</p> Signup and view all the answers

    Which reaction condition is necessary for the successful oxidation of aldehydes in Tollen's test?

    <p>Presence of an alkaline medium</p> Signup and view all the answers

    What is the main distinguishing feature of aldehydes in the Fehling's test?

    <p>Aldehydes reduce Fehling's reagent to give a red precipitate.</p> Signup and view all the answers

    Which of the following aldehydes is NOT mentioned as undergoing the Cannizzaro reaction?

    <p>Acetaldehyde</p> Signup and view all the answers

    What color complex indicates a positive result in the sodium nitroprusside test?

    <p>Red color complex</p> Signup and view all the answers

    What occurs during the Cannizzaro reaction?

    <p>One molecule acts as the reducing agent and another as the oxidizing agent.</p> Signup and view all the answers

    Which of the following statements about ketones in Fehling's test is correct?

    <p>Ketones do not change the color of Fehling's reagent.</p> Signup and view all the answers

    During the polymerization reaction, what indicates a positive result when mixing formaldehyde and resorcinol?

    <p>A reddish violet color or a white ring is formed.</p> Signup and view all the answers

    Which of the following compounds can give a positive result in the Iodoform test?

    <p>Benzyl methyl ketone</p> Signup and view all the answers

    What is the expected result when benzaldehyde is reacted with concentrated hydrochloric acid after the Cannizzaro reaction?

    <p>Benzoic acid is liberated as a white precipitate.</p> Signup and view all the answers

    Study Notes

    Aldehyde and Ketone Identification

    • Aldehydes: Compounds with the general formula RCHO. R can be aliphatic or aromatic. Formaldehyde has a hydrogen atom for R.
    • Ketones: Compounds with the general formula RCOR'. R and R' can be aliphatic or aromatic.
    • Functional Group: Both contain a carbonyl group (C=O), which is key to their chemical and physical properties. Examples of aldehydes include formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, and salicylaldehyde. Ketones include acetone, acetophenone, benzyl methyl ketone, and benzophenone.

    Chemical Reactions

    • 2,4-Dinitrophenylhydrazine (2,4-DNPH) Test: Both aldehydes and ketones react with 2,4-DNPH to form a yellow or orange precipitate. This precipitate is a 2,4-dinitrophenylhydrazone.
    • General Test Procedure: Add 2-3 drops of the compound to 3 drops of the reagent. If the compound is insoluble in water, dissolve it in 1 mL of methanol first.

    Differentiation Tests

    • Tollen's Test: Aldehydes react with Tollen's reagent (ammoniacal silver nitrate) to form a silver mirror (Ag). This reaction involves the oxidation of the aldehyde to a carboxylic acid.
      • Procedure: Add 2-3 drops of the compound to 2-3 mL of Tollen's reagent. Warm the test tube if no reaction occurs.
    • Fehling's Test: Only aldehydes reduce Fehling's reagent (a deep blue solution) to give a red cuprous oxide (Cu₂O) precipitate.
      • Procedure: Add 5 drops of the compound to 1 mL of Fehling’s solution and heat in a water bath for 5 minutes (shake for water insoluble compounds).
    • Important Note: Ketones do not react positively with either Tollen's or Fehling's reagent.

    Special Tests for Terminal Methyl Groups

    • Iodoform Test: This test identifies aldehydes and ketones with a terminal methyl group.
    • Sodium Nitroprusside Test: Also tests for compounds with a terminal methyl group causing a red color
    • Polymerization reaction: Formaldehyde or salicylaldehyde will polymerize with resorcinol in the presence of sulfuric acid.

    Cannizzaro Reaction

    • Conditions: Benzaldehyde, salicylaldehyde, and formaldehyde (no alpha-hydrogen atoms) undergo a self-oxidation-reduction reaction in a strong base (e.g., sodium hydroxide).
    • Products: The reaction produces a mixture of an alcohol and a salt of the corresponding carboxylic acid.
    • Procedure: Add a few drops of aldehyde to 0.5 mL of 30% sodium hydroxide and heat gently for 5 minutes. Then add water and concentrated hydrochloric acid for reaction confirmation.

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    Description

    Test your knowledge on aldehyde and ketone identification, including their structural formulas and reactions. This quiz covers essential tests like 2,4-DNPH and differentiation tests such as Tollen's Test. Perfect for chemistry students looking to strengthen their understanding of organic compounds.

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