Anthrone Test in Carbohydrate Chemistry
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Questions and Answers

What is the main use of the Molisch Test?

  • To evaluate the acidity of a solution
  • To determine the presence of proteins
  • To distinguish between aldose and ketose sugars (correct)
  • To measure the concentration of amino acids

    • What happens during the Anthrone Test for detecting carbohydrates?

  • Sugars undergo oxidation
  • Proteins are precipitated
  • Fats are emulsified
  • Sugars undergo hydrolysis and dehydration (correct)

    • Why should heating be limited to no more than 3 minutes in the Anthrone Test?

  • To ensure positive identification of aldose sugars
  • To prevent loss of volatile compounds
  • To avoid hydrolysis of sugars
  • To prevent the breakdown of carbohydrates (correct)

    • What does the term 'reactivity' refer to in the context of aldose and ketose sugars?

    <p>The speed of reaction with reagents</p> Signup and view all the answers

    What is the role of concentrated sulfuric acid in carbohydrate testing?

    <p>It catalyzes hydrolysis and dehydration of sugars</p> Signup and view all the answers

    What is the initial reaction of polysaccharides when tested?

    <p>Hydrolysis of glycosidic bonds</p> Signup and view all the answers

    What type of medium is typically used when testing for reducing properties of sugars?

    <p>Alkaline medium</p> Signup and view all the answers

    Which of the following substances is not classified as a reducing sugar?

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

    Which compound is produced during the dehydration of hexoses in carbohydrate testing?

    <p>Hydromethyl furfural</p> Signup and view all the answers

    What occurs after the initial oxidation and isomerization of reducing sugars?

    <p>Yielding products with low molecular weight</p> Signup and view all the answers

    Which test is primarily used to detect reducing sugars?

    <p>Benedict's Test</p> Signup and view all the answers

    Which of the following is a characteristic observation in Benedict's Test?

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

    Which reagent is NOT typically used in Benedict's Test?

    <p>Sodium nitrate</p> Signup and view all the answers

    What is the status of polysaccharides with four or more monosaccharide units regarding reducing properties?

    <p>They are typically non-reducing sugars</p> Signup and view all the answers

    Which characteristic makes a sugar non-reducing?

    <p>Lack of a free aldehyde or ketone group</p> Signup and view all the answers

    What happens to aldoses in the presence of weak alkali?

    <p>They are converted into ketoses or other aldoses.</p> Signup and view all the answers

    Which of the following carbohydrates can act as a reducing sugar?

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

    What color complex does amylose form with iodine?

    <p>Deep blue complex</p> Signup and view all the answers

    Which sugar is produced as a result of the iodine test?

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

    What is the expected result of a Benedict's test on these sugars?

    <p>Positive result</p> Signup and view all the answers

    What type of crystals are yielded from a phenylhydrazine test?

    <p>Glucosazone crystals</p> Signup and view all the answers

    What color is the complex formed with glycogen during the iodine test?

    <p>Reddish brown complex</p> Signup and view all the answers

    What happens to the color of the solution when glucose is mixed with Ba(OH)2 before inversion?

    <p>It turns blue.</p> Signup and view all the answers

    How can one identify a sugar by its structure?

    <p>By a pattern of hydroxyl groups.</p> Signup and view all the answers

    Which type of sugars are resistant to oxidation by general oxidizing agents?

    <p>Sugars containing only glycosidic linkages.</p> Signup and view all the answers

    What happens to the active group of reducing sugars when heated in the presence of certain metallic ions?

    <p>It is oxidized and metallic ions are reduced.</p> Signup and view all the answers

    What is the role of enediols in the reduction process of cupric ions?

    <p>They reduce cupric ions to cuprous form.</p> Signup and view all the answers

    What forms when cuprous ions combine with hydroxide ions due to the reaction with reducing sugars?

    <p>Yellow cuprous hydroxide.</p> Signup and view all the answers

    What is produced when reducing sugars are oxidized in an alkaline condition?

    <p>Enediols.</p> Signup and view all the answers

    Which oxidizing agents are mentioned as contributors to the oxidation of reducing sugars?

    <p>Cupric and Bismuth.</p> Signup and view all the answers

    What color does cuprous hydroxide turn upon heating?

    <p>Red.</p> Signup and view all the answers

    What is a characteristic of reducing disaccharides regarding their structure?

    <p>They have at least one free aldehyde or ketone group.</p> Signup and view all the answers

    What is produced when aldehyde or ketone groups in sugar are boiled with an alkali?

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

    Which reagent is commonly used in the oxidation of monosaccharides to yield soluble dicarboxylic acid?

    <p>Nitric acid</p> Signup and view all the answers

    What is an expected result when galactose is oxidized?

    <p>It yields soluble dicarboxylic acid</p> Signup and view all the answers

    What happens to a sugar when it is boiled with sodium hydroxide ammonia?

    <p>It undergoes tautomerization</p> Signup and view all the answers

    What color is usually associated with the production of caramel from sugars?

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

    Study Notes

    Detection of Carbohydrates

    • Carbohydrates can be detected using Molisch's test or Anthrone test.
    • Anthrone test distinguishes between aldose and ketose sugars, with ketoses being more reactive.
    • Concentrated sulfuric acid hydrolyzes glycosidic bonds and dehydrates monosaccharides to form furfural (pentoses) or hydromethyl furfurals (hexoses).

    Reducing Properties of Sugars

    • Reducing sugars possess free aldehyde or ketone groups, allowing them to reduce metallic ions.
    • Reduction of metallic ions during heating leads to color changes:
      • Apple green indicates traces
      • Yellow indicates a plus one result
      • Orange indicates a plus two result
      • Red indicates a plus three result
    • Cuprous hydroxide forms complexes with sugars, leading to visible color changes in tests.

    Reducing vs Non-Reducing Disaccharides

    • All monosaccharides and disaccharides are reducing sugars, except sucrose.
    • Polysaccharides with four or more monosaccharide units are considered non-reducing.

    Common Tests for Reducing Sugars

    • Benedict's test uses copper acetate, copper sulfate, acetic acid, sodium hydroxide, and sodium nitrate.
    • Observing scanty red precipitate (cuprous oxide) indicates positive results for monosaccharides.
    • Barfoed’s Test reveals reducing disaccharides.

    Aldaric Acid Formation

    • When reducing sugars are boiled with alkali, they undergo tautomerization to form caramel.
    • Aldaric acid results from oxidation of both aldehyde and primary alcohol to carboxylic acids.

    Sugar Interconversion

    • Aldoses can convert to ketoses and vice versa in the presence of weak alkali.
    • Interconversion leads to equal amounts of glucose, mannose, and fructose at equilibrium.

    Iodine Test for Polysaccharides

    • Iodine forms a coordinate complex with helical structures of polysaccharides.
    • Complex colors:
      • Amylose: Deep blue complex
      • Amylopectin: Purple complex
      • Glycogen: Reddish brown complex
      • Erythrodextrin: Red complex
      • Achrodextrin: Colorless

    Starch Hydrolysis

    • Hydrolysis of starch can be noted and classified based on the pattern of hydroxyl groups in sugar structure.
    • Inversion of sucrose can be studied through reactions involving Ba(OH)2 and water to monitor color changes.

    Tip for Sugar Identification

    • Analyze and use the pattern of hydroxyl groups in a sugar's structure to determine its classification.

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    Description

    Explore the Anthrone Test, a method used to detect carbohydrates in a solution. This quiz will cover the principles of the test, including how concentrated sulfuric acid interacts with carbohydrates. Test your knowledge of distinguishing aldoses and understanding the significance of carbohydrates in chemistry.

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