AQA A-Level Chemistry 7405
Atomic Structure
Amount of Substance
Bonding
Energetics and Thermodynamics
Kinetics
Chemical Equilibria
Redox and Electrochemistry
Acids and Bases
Periodicity and Group Chemistry
Period 3 Elements and Their Oxides
Transition Metals
Introduction to Organic Chemistry
Hydrocarbons
Halogenoalkanes, Alcohols and Organic Analysis
Carbonyls, Carboxylic Acids and Derivatives
Aromatic Chemistry and Amines
Polymers, Amino Acids, Proteins and DNA
Organic Synthesis, NMR and Chromatography
Halogenoalkanes, Alcohols and Organic Analysis
Distinguishing Aldehydes and Ketones
- 3 things to know
- Papers 2 and 3
Overview
Fehling's and Tollens' reagents, and the observations that separate the two.
What you need to know
Answer each one before you reveal it.
What observation indicates a positive result when Tollens' reagent reacts with an aldehyde?
What observation indicates a positive result when Fehling's solution reacts with an aldehyde?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What reagent is used to distinguish between aldehydes and ketones?
Model answer
Tollens' reagent or Fehling's solution
- 2
What observation indicates a positive result when Tollens' reagent reacts with an aldehyde?
Model answer
A silver mirror forms on the inside of the test tube
- 3
What observation indicates a positive result when Fehling's solution reacts with an aldehyde?
Model answer
A brick-red precipitate forms
- 4
Why do ketones not react with Tollens' reagent?
Model answer
Ketones cannot be oxidised by mild oxidising agents as they have no hydrogen atom attached to the carbonyl carbon
- 5
Why do ketones not react with Fehling's solution?
Model answer
Ketones cannot be oxidised by mild oxidising agents as they have no hydrogen atom attached to the carbonyl carbon
- 6
What is the chemical basis for Tollens' reagent being able to distinguish aldehydes from ketones?
Model answer
Tollens' reagent is a mild oxidising agent that can oxidise aldehydes but not ketones
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