Questions and Answers
The result of the iodine test with 5ml of sugar and 2 drops of iodine is a blue color.
True
The Fehling test is used to measure the presence of starch in a solution.
False
A violet ring forms at the junction of the two solutions when conducting the Molish test.
True
The Molish test involves a solution containing iodine.
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A blue color observed in the iodine test indicates the presence of sugar.
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Sucrose is composed of α-glucose and β-fructose joined by an α 1 - β 2 glycosidic bond.
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Fructose is classified as an aldo-reducing sugar.
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The glycosidic bond in sucrose involves two aldehyde groups.
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Glucose is classified as a keto-reducing sugar.
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The structural formula of sucrose can be represented as α-glucose + β-fructose.
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1 ml of sugar combined with 3 ml of Barfoid reagent does not result in a reaction after 4 minutes.
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Barfoid reagent is used to test for the presence of reducing sugars.
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A observation after 4 minutes indicates that the sugar has been reduced.
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The reaction time for investigating reducing sugars with Barfoid reagent is typically less than 4 minutes.
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Mixing 1 ml of sugar with 3 ml of Barfoid reagent is an inappropriate amount for testing reducing sugars.
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The general test for carbohydrates involves adding 3 ml of sugar and 3 drops of alpha naphthol.
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Alpha naphthol should be added after the concentrated H2SO4 in the carbohydrate test.
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The concentrated H2SO4 is added slowly to the sugar and alpha naphthol mixture.
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Shaking the mixture well is an unnecessary step in the general test for carbohydrates.
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The observation of the test occurs before adding concentrated H2SO4.
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Sucrose has a red precipitate in the Fehling test.
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Fructose is identified as a reducing sugar in the Fehling test.
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Starch is colorless and odorless when examined physically.
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Lactose gives a violet ring in the Molish test.
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Glucose produces a blue color in the iodine test.
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All carbohydrates are colorless, odorless, and clear except starch.
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A positive result in the Seliwanoff test indicates the presence of a reducing sugar.
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The iodine test reveals a blue color in the presence of starch.
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Barfoid test results indicate sucrose is a monosaccharide.
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All sugars tested have neutral reactions.
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Study Notes
Sucrose Composition
- Sucrose is formed from α-glucose and β-fructose through an α1-β2 glycosidic bond.
- Fructose is categorized as a keto-reducing sugar; glucose is an aldo-reducing sugar.
General Tests for Carbohydrates
- Molish Test: Mix 3 ml of sugar with 3 drops of alpha naphthol, shake, and add 2 ml of concentrated H2SO4 slowly. A violet ring indicates a positive result for carbohydrates.
- Iodine Test: Adding 5 ml of sugar with 2 drops of iodine produces a blue color if starch is present.
- Fehling Test: Mix 1 ml of sugar with 3 ml of Barfoid reagent and wait 4 minutes; visual observations assess reduction.
Physical Characteristics of Carbohydrates
- Most carbohydrates are colorless, odorless, clear, and neutral, except for starch, which is whitish and turbid.
Glucose Identification
- Physical Properties: Colorless, odorless, clear solution, neutral reaction.
- Chemical Tests:
- Biuret Test: No violet color indicates it's not a protein.
- Molish Test: Violet ring confirms it's a carbohydrate.
- Iodine Test: No blue color shows it's not starch.
- Fehling Test: Red precipitate confirms it is a reducing sugar.
- Benedict Test: Red precipitate confirms it's a reducing sugar.
- Barfoid Test: Produces a red precipitate and red fumes, indicating it's a monosaccharide.
- Seliwanoff Test: No red color shows it's not a keto-sugar.
Fructose Identification
- Physical Properties: Colorless, odorless, clear solution, neutral reaction.
- Chemical Tests: Identical results to glucose, with a defining Seliwanoff Test producing red color indicating it is a keto sugar.
Lactose Identification
- Physical Properties: Colorless, odorless, clear solution, neutral reaction.
- Chemical Tests:
- Results similar to glucose; red precipitate in Fehling and Benedict tests confirms it is a reducing sugar.
- No red precipitate in Barfoid Test indicates it's not a monosaccharide.
Sucrose Identification
- Physical Properties: Colorless, odorless, clear solution, neutral reaction.
- Chemical Tests:
- No violet in Biuret Test confirms it's not a protein.
- Molish Test shows violet ring indicating a carbohydrate.
- No blue color in Iodine Test confirms no starch.
- No red precipitate in Fehling and Benedict tests indicates it's not a reducing sugar.
- Upon acid hydrolysis and after neutralization, sucrose is broken down into glucose and fructose, registered as reducing sugars in Fehling and Seliwanoff tests, respectively.
Starch Identification
- Physical Properties: Whitish, odorless, turbid solution, neutral reaction.
- Chemical Tests:
- No violet color in Biuret Test indicates no protein.
- Molish Test shows violet ring confirming carbohydrate presence.
- Blue color in Iodine Test indicates starch is present.
- No red precipitate in Fehling and Benedict tests shows it's not a reducing sugar.
- Acid hydrolysis confirms starch hydrolyzes to glucose, confirmed by red precipitate in Fehling Test and no blue color in Iodine Test.
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Description
Explore the composition, tests, and characteristics of carbohydrates through this quiz. Delve into sucrose formation, various identification tests, and the physical properties of carbohydrates. Enhance your understanding of glucose and fructose in a fun and educational way.
