Qualitative Tests for Carbohydrates PDF
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Uploaded by GoldZirconium
Chinese General Hospital Colleges
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Summary
This document describes an experiment on qualitative tests used to identify different types of carbohydrates. The materials required, including various reagents, are listed; procedures for each test are outlined, identifying positive results for each. It also features question prompts related to this experiment. This is not a past paper.
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**QUALITATIVE TESTS FOR CARBOHYDRATES** **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 Rea...
**QUALITATIVE TESTS FOR CARBOHYDRATES** **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 1\. Prepare test tubes containing 3 ml of the following: - Xylose - Glucose - Starch - Lactose - Fructose Use the above samples for each qualitative test. 2\. Use the procedures below for the qualitative testing. **\ ** +-----------------------+-----------------------+-----------------------+ | Test | Procedure | Positive Result | +=======================+=======================+=======================+ | Molisch's Test | 1. There should be a | Purple ring | | | control of which | | | | 4 ml of distilled | | | | water is mixed | | | | with 2 drops of | | | | Molisch's | | | | reagent. | | | | | | | | 2. Add 2 drops of | | | | Molisch's reagent | | | | to 4 ml of a | | | | sample. | | | | | | | | 3. Add 5 ml of | | | | concentrated | | | | H2SO4 to the test | | | | tube while it is | | | | inclined. Allow | | | | the acid to run | | | | down the side of | | | | the tube. Note | | | | the color of the | | | | ring formed at | | | | the junction of | | | | the two liquids. | | | | | | | | 4. Do the same with | | | | the control. | | +-----------------------+-----------------------+-----------------------+ | Bial's Orcinol Test | 1. Add 3 ml of | Blue green color | | | Bial's reagent to | | | | 1 ml of the | | | | sample. | | | | | | | | 2. Heat the test | | | | tube over a | | | | Bunsen burner | | | | until the | | | | solution begins | | | | to boil. Add 2 | | | | drops of 10% | | | | FeCl3 solution. | | | | Note the color. | | +-----------------------+-----------------------+-----------------------+ | Seliwanoff's Test | 1. Add 4 ml of | Red or pink | | | Seliwanoff's | | | | reagent to 1 ml | | | | of sample. | | | | | | | | 2. Place the test | | | | tube in a boiling | | | | water. Wait for a | | | | minute then note | | | | the changes. | | | | | | | | 3. Continue heating | | | | and observe the | | | | changes at | | | | one-minute | | | | intervals. | | +-----------------------+-----------------------+-----------------------+ | Benedict's Test | 1. Add 5 ml of | Formation of | | | Benedict's | precipitate | | | reagent to 1 ml | | | | of sample. | | | | | | | | 2. Place the test | | | | tube in a boiling | | | | water bath for 3 | | | | minutes. Observe | | | | the color of the | | | | solution and | | | | possible | | | | appearance of | | | | precipitates. | | +-----------------------+-----------------------+-----------------------+ | Barfoed's Test | 1. Add 3 ml of | Red coloration | | | Barfoed's reagent | | | | t 1 ml of sample. | | | | | | | | 2. Place the test | | | | tube in a boiling | | | | water bath for 10 | | | | minutes. | | +-----------------------+-----------------------+-----------------------+ | Tollen's test | 1. Add 2 ml of | Appearance of a | | | Tollen's reagent | silver mirror | | | to 5 drops of | | | | sample. | | | | | | | | 2. Add dilute NH4OH | | | | until the brown | | | | precipitate of | | | | silver oxide | | | | dissolves. | | | | | | | | 3. Place the test | | | | tube in a boiling | | | | water bath for 5 | | | | minutes. | | +-----------------------+-----------------------+-----------------------+ | Iodine Test | 1. Add a few drops | Bluish-black color | | | of 0.01 M iodine | | | | solution into 0.5 | | | | mL of sample. | | | | | | | | 2. Heat sample in a | | | | water bath and | | | | observe change. | | +-----------------------+-----------------------+-----------------------+ QUESTIONS: 1. What makes carbohydrates reactive? 2. What are reducing sugars? 3. What are the differences observed from the different samples?
