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Questions and Answers
What color change is observed when Barfoed's reagent reacts with a sugar solution?
What color change is observed when Barfoed's reagent reacts with a sugar solution?
- Yellow to brown
- Colorless to blue
- Blue to red (correct)
- Blue to green
What is the correct concentration ratio for Barfoed's reagent preparation?
What is the correct concentration ratio for Barfoed's reagent preparation?
- 13.3 g copper acetate in 100 ml water with 1.8 ml glacial acetic acid
- 13.3 g copper acetate in 200 ml water with 1.8 ml glacial acetic acid (correct)
- 13.3 g copper acetate in 100 ml water with 0.9 ml glacial acetic acid
- 1.8 g copper acetate in 200 ml water with 13.3 ml glacial acetic acid
Which of the following statements is true about the iodine test for polysaccharides?
Which of the following statements is true about the iodine test for polysaccharides?
- Iodine solution gives a blue color with starch and a brown color with glycogen. (correct)
- Iodine solution becomes colorless with glycogen and brown with starch.
- Iodine solution turns red with glycogen and blue-black with starch.
- Iodine solution turns blue with glycogen and brown with starch.
Study Notes
Carbohydrate Tests
- Two tests are described to identify carbohydrates: Barfoed's Test and Iodine's Test
Barfoed's Test
- Materials: Carbohydrate solutions (1 g/l and 10 g/l), Barfoed's reagent, beaker, test tubes, graduated pipettes, funnel, filter paper, and watchglass
- Procedure: Mix 2ml of sugar solution with 1ml of Barfoed's reagent, boil for 3 minutes, and cool to observe a brick red precipitate
- Indicator: Formation of a brick red precipitate
Iodine's Test
- Materials: Carbohydrate solutions (1 g/l and 10 g/l), Iodine's solution, beaker, test tubes, graduated pipettes, funnel, paper, and watchglass
- Procedure: Add 1-2 drops of iodine solution to 3 mL of polysaccharide solution and observe the color change
- Indicators:
- Blue color with starch that disappears on heating and reappears on cooling
- Brown color with glycogen
- Formation of a blue-black complex with polysaccharides
Key Points
- Barfoed's Test is specific for reducing sugars
- Iodine's Test is specific for detecting starch and glycogen
- Different polysaccharides produce different color results with the iodine test
- Heating and cooling affect the color formation in Iodine's Test
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Description
Identify the procedures and materials used in testing carbohydrates using Barfoed's and Iodine's tests. Understand the chemical reactions and observations involved.
