Q9. After performing the experiment with glucose and bromine water, which statements are correct?

Background

Topic: Functional groups and chemical reactivity of carbohydrates (glucose, fructose, aldehydes).

This question tests your understanding of the chemical properties of glucose, especially its aldehyde group, and how it reacts with bromine water. It also asks you to compare glucose with other compounds like fructose and formic aldehyde.

Key Terms and Formulas

• Aldehyde group (-CHO): A functional group present in glucose's open-chain form, responsible for its reducing properties.

• Bromine water (Br2/H2O): A mild oxidizing agent used to test for aldehydes.

• Reaction:

Step-by-Step Guidance

1. Recall that glucose in its open-chain form contains an aldehyde group, which can be oxidized by bromine water.

2. When bromine water reacts with an aldehyde, the solution loses its characteristic color, but does not form a precipitate.

3. Fructose contains a ketone group, which does not react with bromine water under these conditions, so the color remains.

4. Formic aldehyde (methanal) also reacts with bromine water, causing decolorization, so this test cannot distinguish between glucose and formic aldehyde.

5. Review each statement and use your understanding of the reactions to determine which are correct or incorrect, but stop before marking the answers.

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Q10. After performing the experiment with glucose and bromine water, which statements are correct?

Background

Topic: Oxidation of glucose, identification of reaction products, and functional group analysis.

This question tests your knowledge of the products formed when glucose reacts with bromine water, and the chemical nature of glucose.

Key Terms and Formulas

• Gluconic acid: The organic product formed when glucose is oxidized by bromine water.

• Polyalcohol: A compound with multiple hydroxyl groups; glucose is a polyalcohol but the reaction here tests its aldehyde group.

• Oxidation: The process where glucose's aldehyde group is converted to a carboxylic acid.

• Reaction:

Step-by-Step Guidance

1. Identify the organic product formed after the reaction: the aldehyde group in glucose is oxidized to a carboxylic acid (gluconic acid).

2. Consider whether the experiment demonstrates glucose's polyalcohol properties or its aldehyde properties.

3. Determine if the reaction involves oxidation or reduction of glucose.

4. Think about whether this experiment can distinguish between glucose and fructose, based on their reactivity with bromine water.

5. Review each statement and use your understanding to decide which are correct, but stop before marking the answers.

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Q12. In a practical test, students are asked to identify two solutions (X and Y) as glucose 1% or fructose 1%. Which statements are correct?

Background

Topic: Functional group analysis, oxidation-reduction reactions, and identification of carbohydrates.

This question tests your ability to interpret experimental results to distinguish between glucose and fructose, and to understand the chemical basis for the observed phenomena.

Key Terms and Formulas

• Hydroxy groups: Both glucose and fructose have multiple adjacent hydroxyl groups, which can form colored complexes with CuSO4 in alkaline solution.

• Aldehyde group: Glucose has an aldehyde group; fructose does not, but can isomerize under alkaline conditions.

• Oxidation-reduction reactions: Both reactions with CuSO4/NaOH and bromine water involve redox processes.

• Key reactions:

Step-by-Step Guidance

1. In step 2, both glucose and fructose form a blue solution with CuSO4 in alkaline medium, indicating the presence of adjacent hydroxyl groups.

2. In step 3, heating causes both solutions to form a red precipitate (Cu2O), showing that both can act as reducing sugars under these conditions.

3. In step 4, only glucose reacts with bromine water, causing decolorization; fructose does not, so the color remains.

4. Use the results from step 4 to identify which solution is glucose and which is fructose.

5. Consider whether the reactions in steps 2 and 3 are redox reactions.

6. Review each statement and use your understanding to decide which are correct, but stop before marking the answers.

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