Benedict's Test for Reducing Sugars
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Questions and Answers

What is the primary reason why some sugars like glucose are called reducing sugars?

  • They lack any functional groups.
  • They contain complex carbohydrates.
  • They have free ketone or aldehyde groups. (correct)
  • They are incapable of transferring hydrogens.

Which component in Benedict's reagent provides the necessary alkaline conditions?

  • Sodium bicarbonate
  • Sodium carbonate (correct)
  • Sodium hydroxide
  • Sodium chloride

What color change occurs in a positive Benedict's test?

  • Yellow to blue
  • Blue to orange red/ brick red (correct)
  • Green to blue
  • Blue to green

Which of the following sugars does not react with Benedict's reagent?

<p>Sucrose (D)</p> Signup and view all the answers

What is the role of sodium citrate in Benedict's reagent?

<p>To form complexes with copper(II) ions (B)</p> Signup and view all the answers

In the context of Benedict's test, which of the following is not a reducing sugar?

<p>Starch (C)</p> Signup and view all the answers

Flashcards

Reducing Sugars

Sugars with a free ketone or aldehyde group, capable of reducing other substances.

Benedict's reagent

A solution used to detect the presence of reducing sugars.

Sodium carbonate

Component of Benedict's reagent, providing alkaline conditions for the test.

Positive Benedict's test

Results in a color change from blue to orange/red-brick.

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Non-reducing sugar

A sugar that does not react with Benedict's reagent.

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Sucrose

An example of a non-reducing sugar.

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Sodium citrate

Stailizes the copper(II) ions in Benedict's reagent preventing precipitation.

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Benedict's test

A chemical test to identify reducing sugars based on color change.

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Reducing sugar

Sugar with free ketone or aldehyde group able to donate electrons/reduce another substance.

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Starch

A non-reducing sugar.

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Study Notes

Benedict's Test

  • Identifies reducing sugars (monosaccharides) with free ketone or aldehyde functional groups.
  • Reducing sugars, like glucose, can transfer hydrogens (electrons) to other compounds, causing a reduction reaction.

Characteristics of Reducing Sugars

  • All monosaccharides are reducing sugars due to their exposed carbonyl group.
  • Some disaccharides, like sucrose, are non-reducing sugars and won't react with Benedict's reagent.
  • Large polymers of glucose, such as starch, are not reducing sugars.

Principle of Benedict's Test

  • Heating Benedict's solution with simple carbohydrates causes a color change to orange-red/brick-red.
  • Copper (II) ions in the solution are reduced to Copper (I) ions, leading to the color change.
  • Red copper(I) oxide formed is insoluble in water and precipitates out of solution, forming a precipitate.

Benedict Reagent

  • Sodium carbonate provides alkaline conditions necessary for the redox reaction.
  • Sodium citrate complexes with copper (II) ions to prevent deterioration to copper(I) ions during storage.

Objective and Specificity

  • The objective of Benedict's test is to distinguish between reducing and non-reducing sugars.
  • Benedict's test is specific for reducing sugars.

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Description

Identify reducing sugars with Benedicts reagent. Learn about monosaccharides, reduction reactions and color changes.

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