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Questions and Answers
What is the general formula for aldehydes?
What is the general formula for aldehydes?
RCHO
What is the general formula for ketones?
What is the general formula for ketones?
RCOR'
The group R in an aldehyde can be aliphatic or aromatic.
The group R in an aldehyde can be aliphatic or aromatic.
True
What functional group is present in both aldehydes and ketones?
What functional group is present in both aldehydes and ketones?
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Which of the following are examples of aldehydes?
Which of the following are examples of aldehydes?
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Which of the following are examples of ketones?
Which of the following are examples of ketones?
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What reagent is used in the general test for both aldehydes and ketones?
What reagent is used in the general test for both aldehydes and ketones?
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Both aldehydes and ketones give a yellow or orange precipitate with 2,4-Dinitrophenylhydrazine.
Both aldehydes and ketones give a yellow or orange precipitate with 2,4-Dinitrophenylhydrazine.
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What is the name of the precipitate formed when 2,4-Dinitrophenylhydrazine reacts with aldehydes or ketones?
What is the name of the precipitate formed when 2,4-Dinitrophenylhydrazine reacts with aldehydes or ketones?
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Tollen's reagent is a combination of silver nitrate solution with ammonium hydroxide in the presence of sodium hydroxide solution.
Tollen's reagent is a combination of silver nitrate solution with ammonium hydroxide in the presence of sodium hydroxide solution.
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What is the main difference between aldehydes and ketones in terms of oxidation?
What is the main difference between aldehydes and ketones in terms of oxidation?
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Tollen's reagent gives a positive result with both aldehydes and ketones.
Tollen's reagent gives a positive result with both aldehydes and ketones.
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When Tollen's reagent is used, what is the resulting product from the oxidation of an aldehyde?
When Tollen's reagent is used, what is the resulting product from the oxidation of an aldehyde?
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What is the visual indication of a positive Tollen's test?
What is the visual indication of a positive Tollen's test?
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Tollen's test requires an alkaline medium.
Tollen's test requires an alkaline medium.
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Why is ammonium hydroxide used in Tollen's reagent?
Why is ammonium hydroxide used in Tollen's reagent?
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Fehling's reagent is a deep blue solution.
Fehling's reagent is a deep blue solution.
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What is the distinguishing visual result of a positive Fehling's test?
What is the distinguishing visual result of a positive Fehling's test?
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Fehling's test is useful for distinguishing between aldehydes and ketones.
Fehling's test is useful for distinguishing between aldehydes and ketones.
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The haloform test is a special test for aldehydes and ketones containing a terminal methyl group.
The haloform test is a special test for aldehydes and ketones containing a terminal methyl group.
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Which of the following compounds are examples of aldehydes or ketones with a terminal methyl group?
Which of the following compounds are examples of aldehydes or ketones with a terminal methyl group?
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The haloform test for aldehydes or ketones is similar to the haloform test for alcohols.
The haloform test for aldehydes or ketones is similar to the haloform test for alcohols.
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What is the name of the test used to detect the presence of a terminal methyl group in aldehydes or ketones?
What is the name of the test used to detect the presence of a terminal methyl group in aldehydes or ketones?
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What is the name of the test that utilizes sodium nitroprusside?
What is the name of the test that utilizes sodium nitroprusside?
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A red color complex formation indicates a positive sodium nitroprusside test.
A red color complex formation indicates a positive sodium nitroprusside test.
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Polymerization is a reaction that can occur with formaldehyde and salicylaldehyde.
Polymerization is a reaction that can occur with formaldehyde and salicylaldehyde.
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What reagent is used in the polymerization reaction for formaldehyde and salicylaldehyde?
What reagent is used in the polymerization reaction for formaldehyde and salicylaldehyde?
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What is the appearance of the polymer formed in the reaction with formaldehyde and resorcinol?
What is the appearance of the polymer formed in the reaction with formaldehyde and resorcinol?
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The Cannizzaro reaction is a self oxidation-reduction reaction.
The Cannizzaro reaction is a self oxidation-reduction reaction.
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The Cannizzaro reaction is specific for aldehydes that do not contain an alpha hydrogen atom.
The Cannizzaro reaction is specific for aldehydes that do not contain an alpha hydrogen atom.
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What are the products of the Cannizzaro reaction?
What are the products of the Cannizzaro reaction?
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The Cannizzaro reaction requires a strong basic medium.
The Cannizzaro reaction requires a strong basic medium.
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Benzaldehyde can undergo the Cannizzaro reaction.
Benzaldehyde can undergo the Cannizzaro reaction.
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Salicylaldehyde can undergo the Cannizzaro reaction.
Salicylaldehyde can undergo the Cannizzaro reaction.
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Acetone can undergo the Cannizzaro reaction.
Acetone can undergo the Cannizzaro reaction.
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What is the product of the Cannizzaro reaction with benzaldehyde?
What is the product of the Cannizzaro reaction with benzaldehyde?
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The Cannizzaro reaction is a useful method for synthesizing carboxylic acids.
The Cannizzaro reaction is a useful method for synthesizing carboxylic acids.
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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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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.
