Carbohydrate Qualitative Tests
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Questions and Answers

What is indicated by the appearance of a silver mirror in the Tollen's reagent test?

  • Presence of reducing sugars (correct)
  • Presence of fructose
  • Presence of non-reducing sugars
  • Absence of carbohydrates

    • What is the purpose of adding dilute NH4OH in the Tollen's reagent test?

  • To dissolve silver oxide precipitate (correct)
  • To initiate the precipitation of silver
  • To neutralize the sample solution
  • To create a more concentrated solution

    • What color change is expected in the iodine test when starch is present?

  • Bluish-black color (correct)
  • Green color
  • Yellow color
  • Red color

    • What demonstrates that a sample contains carbohydrates when using the iodine test?

    <p>Appearance of a bluish-black color</p> Signup and view all the answers

    What is the significance of heating the sample in the iodine test?

    <p>To enhance the reaction rate</p> Signup and view all the answers

    What is the expected positive result for Molisch's test?

    <p>Purple ring</p> Signup and view all the answers

    Which reagent is added to the sample immediately after Molisch's reagent in Molisch's Test?

    <p>Concentrated H2SO4</p> Signup and view all the answers

    What should be prepared first before conducting the Molisch's test?

    <p>4 ml of distilled water mixed with Molisch's reagent</p> Signup and view all the answers

    How should the concentrated H2SO4 be added during the Molisch's test procedure?

    <p>As a layer by running down the side of the tube</p> Signup and view all the answers

    Which carbohydrate samples are included for testing using Molisch's reagent?

    <p>Xylose, Glucose, Starch, Lactose, and Fructose</p> Signup and view all the answers

    Which of the following reagents is used to test for aldoses in carbohydrate qualitative tests?

    <p>Tollen's Reagent</p> Signup and view all the answers

    What role does the distilled water play in the Molisch's test?

    <p>It serves as a control for comparison.</p> Signup and view all the answers

    Which piece of equipment is essential for heating during carbohydrate qualitative tests?

    <p>Bunsen Burner</p> Signup and view all the answers

    What is the expected color change in Bial's Orcinol Test?

    <p>Blue green</p> Signup and view all the answers

    Which reagent is used first in Seliwanoff's Test?

    <p>Seliwanoff's reagent</p> Signup and view all the answers

    What is the purpose of adding FeCl3 solution in Bial's Orcinol Test?

    <p>To initiate a color change</p> Signup and view all the answers

    What should be done after adding Seliwanoff's reagent to the sample?

    <p>Place it in boiling water</p> Signup and view all the answers

    What color is noted as a result of Seliwanoff's Test?

    <p>Red or pink</p> Signup and view all the answers

    What is the first step in conducting Bial's Orcinol Test?

    <p>Adding Bial's reagent to the sample</p> Signup and view all the answers

    What is the significance of waiting for a minute during Seliwanoff's Test?

    <p>To ensure accurate color change observation</p> Signup and view all the answers

    Which step comes after heating the test tube in Bial's Orcinol Test?

    <p>Noting the color of the solution</p> Signup and view all the answers

    What is the first step in conducting Benedict's Test?

    <p>Add 5 ml of Benedict's reagent to 1 ml of sample.</p> Signup and view all the answers

    How long should the test tube be placed in the boiling water bath for Benedict's Test?

    <p>3 minutes</p> Signup and view all the answers

    What characteristic change indicates a positive result in Benedict's Test?

    <p>Formation of a colored precipitate</p> Signup and view all the answers

    What should be observed after adding Barfoed's reagent to the sample?

    <p>Red coloration after heating</p> Signup and view all the answers

    For how long should the test tube be in the boiling water bath during Barfoed's Test?

    <p>10 minutes</p> Signup and view all the answers

    At what intervals should changes be observed during the heating phase in unspecified procedures?

    <p>Every minute</p> Signup and view all the answers

    Which reagent is used in the first step of Barfoed's Test?

    <p>Barfoed's reagent</p> Signup and view all the answers

    What is the observation period for color change when conducting Benedict's Test?

    <p>At 1-minute intervals</p> Signup and view all the answers

    Study Notes

    Carbohydrate Qualitative Tests

    • Materials:
      • Xylose
      • Glucose
      • Starch
      • Lactose
      • Fructose
      • Molisch's Reagent
      • Concentrated H2SO4
      • Bial's Orcinol reagent
      • Seliwanoff's Reagent
      • 10% FeCl3
      • Benedict's Reagent
      • Barfoed's Reagent
      • Tollen's Reagent
      • Diluted NH4OH
      • 0.01M Iodine Solution
      • Water bath
      • Iron Stand and Ring
      • Wire Gauze
      • Bunsen Burner
      • 250 ml Beakers (3)
      • Stirring Rod
      • Dropper
      • Pipette
      • Test Tubes and Rack
      • distilled water
    • Procedure:
      • Prepare five test tubes each containing 3 ml of each sample: Xylose, Glucose, Starch, Lactose, and Fructose.
      • Use each sample for the following qualitative tests
    • Qualitative Tests:
      • Molisch's Test:
        • A control with distilled water and Molisch's reagent
        • Add 2 drops of Molisch's reagent to 4 ml of a sample followed by 5 ml of concentrated H2SO4
        • Positive Result: Purple ring formed at the junction of the liquids
      • Bial's Orcinol Test:
        • Add 3 ml of Bial's reagent to 1 ml of sample and heat in a boiling water bath
        • Add 2 drops of 10% FeCl3 and note the color
        • Positive Result: Blue-green color
      • Seliwanoff's Test:
        • Add 4 ml of Seliwanoff's reagent to 1 mL of sample and place the test tube in a boiling water bath
        • Positive Result: Red or pink coloration
      • Tollen's Test:
        • Add 2 ml of Tollen's reagent to 5 drops of a sample
        • Add dilute NH4OH until brown precipitate of silver oxide dissolves
        • Place the test tube in a boiling water bath for 5 minutes
        • Positive Result: Appearance of a silver mirror
      • Benedict's Test:
        • Add 5 ml of Benedict's reagent to 1 ml of sample
        • Place the test tube in a boiling water bath for 3 minutes and observe the color
        • Positive Result: Formation of precipitate
      • Barfoed's Test:
        • Add 3 ml of Barfoed's reagent to 1 ml of sample
        • Place the test tube in a boiling water bath for ten minutes
        • Positive Result: Red coloration
      • Iodine Test:
        • Add a few drops of 0.01 M iodine solution into 0.5 mL of a sample
        • Heat the sample in a water bath and observe
        • Positive Result: Bluish-black color

    Carbohydrate Reactivity

    • The presence of a free carbonyl group (aldehyde or ketone) makes carbohydrates reactive.

    Reducing Sugars

    • Reducing sugars are carbohydrates that have a free aldehyde or ketone group and can reduce other compounds.
    • They are able to donate electrons and reduce other molecules.

    Carbohydrate Sample Test Results

    • The differences observed from the different samples are due to the specific chemical structures of each carbohydrate and their ability to react with the reagents used in the tests.
    • For example, Monosaccharides with a free anomeric hydroxyl group are strong reducing agents.
      • This is why glucose and fructose will give a positive Benedict's test, while starch and lactose will not.
    • Disaccharides such as lactose are also reducing sugars
      • This is because one of the anomeric hydroxyl groups is free.
    • Starch is a polysaccharide, and has a glycosidic bond, making it a non-reducing sugar.
      • This is why starch will not give a positive Benedict's test.
    • The differences in color changes observed in the tests can indicate whether the carbohydrate is a reducing sugar or a non-reducing sugar.
    • The tests allow for the identification of different structural features of carbohydrate molecules.

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    Related Documents

    Qualitative Tests for Carbohydrates PDF

    Description

    This quiz covers various qualitative tests for carbohydrates using substances like xylose, glucose, and starch. Participants will learn about different reagents and their applications in detecting sugars and polysaccharides. Familiarity with laboratory procedures and reagents is essential for performing these tests accurately.

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