Identification of Aldehydes and Ketones
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Questions and Answers

What is the general formula for aldehydes?

RCHO

What is the general formula for ketones?

RCOR'

The group R in an aldehyde can be aliphatic or aromatic.

True

What functional group is present in both aldehydes and ketones?

<p>carbonyl group (C=O)</p> Signup and view all the answers

Which of the following are examples of aldehydes?

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

Which of the following are examples of ketones?

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

What reagent is used in the general test for both aldehydes and ketones?

<p>2,4-Dinitrophenylhydrazine</p> Signup and view all the answers

Both aldehydes and ketones give a yellow or orange precipitate with 2,4-Dinitrophenylhydrazine.

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

What is the name of the precipitate formed when 2,4-Dinitrophenylhydrazine reacts with aldehydes or ketones?

<p>2,4-Dinitrophenylhydrazone</p> Signup and view all the answers

Tollen's reagent is a combination of silver nitrate solution with ammonium hydroxide in the presence of sodium hydroxide solution.

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

What is the main difference between aldehydes and ketones in terms of oxidation?

<p>Aldehydes are easily oxidized while ketones are not.</p> Signup and view all the answers

Tollen's reagent gives a positive result with both aldehydes and ketones.

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

When Tollen's reagent is used, what is the resulting product from the oxidation of an aldehyde?

<p>A carboxylic acid</p> Signup and view all the answers

What is the visual indication of a positive Tollen's test?

<p>A silver mirror</p> Signup and view all the answers

Tollen's test requires an alkaline medium.

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

Why is ammonium hydroxide used in Tollen's reagent?

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

Fehling's reagent is a deep blue solution.

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

What is the distinguishing visual result of a positive Fehling's test?

<p>A red cuprous oxide precipitate</p> Signup and view all the answers

Fehling's test is useful for distinguishing between aldehydes and ketones.

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

The haloform test is a special test for aldehydes and ketones containing a terminal methyl group.

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

Which of the following compounds are examples of aldehydes or ketones with a terminal methyl group?

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

The haloform test for aldehydes or ketones is similar to the haloform test for alcohols.

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

What is the name of the test used to detect the presence of a terminal methyl group in aldehydes or ketones?

<p>Iodoform test</p> Signup and view all the answers

What is the name of the test that utilizes sodium nitroprusside?

<p>Sodium nitroprusside test</p> Signup and view all the answers

A red color complex formation indicates a positive sodium nitroprusside test.

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

Polymerization is a reaction that can occur with formaldehyde and salicylaldehyde.

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

What reagent is used in the polymerization reaction for formaldehyde and salicylaldehyde?

<p>Concentrated sulfuric acid</p> Signup and view all the answers

What is the appearance of the polymer formed in the reaction with formaldehyde and resorcinol?

<p>Reddish violet</p> Signup and view all the answers

The Cannizzaro reaction is a self oxidation-reduction reaction.

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

The Cannizzaro reaction is specific for aldehydes that do not contain an alpha hydrogen atom.

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

What are the products of the Cannizzaro reaction?

<p>An alcohol and a carboxylic acid</p> Signup and view all the answers

The Cannizzaro reaction requires a strong basic medium.

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

Benzaldehyde can undergo the Cannizzaro reaction.

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

Salicylaldehyde can undergo the Cannizzaro reaction.

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

Acetone can undergo the Cannizzaro reaction.

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

What is the product of the Cannizzaro reaction with benzaldehyde?

<p>Benzyl alcohol and sodium benzoate</p> Signup and view all the answers

The Cannizzaro reaction is a useful method for synthesizing carboxylic acids.

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

Study Notes

Identification of Aldehydes and Ketones

  • 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.
  • Common carbonyl group (C=O): This group is present in both aldehydes and ketones and is responsible for their key chemical and physical properties.
  • Examples of aldehydes: Formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, salicylaldehyde.
  • Examples of ketones: Acetone, acetophenone, benzyl methyl ketone, 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 test is used for the general identification of both functional groups.

Differentiation Tests (Aldehyde vs. Ketone)

  • Aldehydes react with oxidizing agents (Tollen's and Fehling's reagents) whereas ketones do not.
  • Tollen's test:
    • Reacts with ammonical silver nitrate solution.
    • Oxidation of the aldehyde produces a carboxylic acid.
    • Silver ions are reduced to form a silver mirror.
    • Procedure is to mix the compound with Tollen's reagent and observe if a silver mirror is formed; if not, warm the mixture gently.
  • Fehling's test:
    • Uses Fehling's solution (complex solution involving copper ions).
    • Only aldehydes react by reducing the copper(II) ions to red copper oxide (Cu2O) precipitate.
    • Aldehydes change color from blue to green and then precipitate in a red color.
    • Procedure is to mix the compound with Fehling's reagent and heat the mixture for 5 minutes in a water bath. Observe for color change and a red precipitate.

Special Tests for Terminal Methyl Groups

  • Iodoform Test: Identifies compounds with a terminal methyl group in ketones. Specific procedure is required; check for details.
  • Sodium Nitroprusside Test: Used to identify compounds with terminal methyl groups. Procedure: add sodium nitroprusside solution to the compound followed by excess 30% NaOH solution. A positive result is a red or reddish violet color complex.

Cannizzaro Reaction

  • Certain aldehydes (benzaldehyde, salicylaldehyde, and formaldehyde) can undergo a self-oxidation-reduction reaction in basic conditions to produce both an alcohol and a carboxylate salt.
  • This test allows for the aldehyde identification but note that testing formaldehyde with this method is not suitable. Formaldehyde, for example, produces formic acid which is liquid rather than a solid, therefore not suitable for comparison.

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Identification Of Aldehydes And Ketones PDF

Description

This quiz focuses on distinguishing between aldehydes and ketones based on their structures and chemical properties. You will explore key reactions, including the 2,4-DNPH test, and learn how to identify these compounds through various tests. Suitable for chemistry students looking to deepen their understanding of organic compounds.

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