Since it can detect the presence of a reducing sugar, Benedict’s solution can be used to distinguish between aldehydes and ketones. An illustration detailing the reaction between an aldose and Benedict’s reagent that results in the formation of cuprous oxide is provided above. Sugar needs to be decomposed into its components glucose and fructose then the glucose test would be positive but the starch test would still be negative. A color change would signify the presence of a reducing sugar.[2]. Place inside the test tube 1 ml of sample. The final product can be employed to check for the presence of reducing sugars. 2 ml (10 drops) of Benedict’s reagent (CuSO4) is placed in the test tube. (g) Sodium Nitroprusside Test: Dissolve sodium nitroprusside in distilled water in a clean test tube. To learn more about Benedict’s test and other important chemical tests (such as Molisch’s test), register with BYJU’S and download the mobile application on your smartphone. Therefore, simple carbohydrates containing a free ketone or aldehyde functional group can be identified with this test. Add 2 mL of 3 M sodium hydroxide and then slowly add 3 mL of the iodine solution. The color varies from green to dark red (brick) or rusty-brown, depending on the amount of and type of sugar. [2] Such tests that use this reagent are called the Benedict's tests. A greenish precipitate indicates about 0.5 g% concentration; yellow precipitate indicates 1 g% concentration; orange indicates 1.5 g% concentration; and red indicates 2 g% or higher concentration. Benedict’s quantitative reagent contains potassium thiocyanate and is used to determine how much reducing sugar is present. Test For Reducing Sugars: ketone. However, a positive reaction can also be given by the presence of ascorbic acid, homogentisic acid, and other reducing substances urine. The presence of other reducing substances also gives a positive result. During a water bath, which is usually 4–10 minutes, the solution should progress through the colors of blue (with no reducing sugar present), orange, yellow, green, red, and then brick red precipitate or brown (if a high concentration of reducing sugar is present). The titration should be repeated with 1% glucose solution instead of the sample for calibration. The reducing sugar can be either a monosaccharide or a disaccharide. [5] Sodium citrate acts as a complexing agent which keeps Cu2+ in solution since it would otherwise precipitate as cupric carbonate. Hendrix College- Benedicts Test for Glucose. If the substance to be tested is water soluble, dissolve 4 drops of a liquid or an estimated 50 mg of a solid in 2 mL of water in a large test tube. 2. Sucrose (table sugar) contains two sugars (fructose and glucose) joined by their glycosidic bond in such a way as to prevent the glucose undergoing isomerization to an aldehyde, or fructose to alpha-hydroxy-ketone form. Widal Test- Introduction, Principle, Procedure,…, Benedict’s Test- Principle, Composition,…, Different Size, Shape and Arrangement of Bacterial Cells, Nutrient Agar: Composition, Preparation and Uses, MacConkey Agar- Composition, Principle, Uses,…, Differences between Gram Positive and Gram Negative Bacteria. , – fellow pre-med student trying to pass pharmacy, ohh no worries at all, hope you are enjoying your results XDXDXD. The end result of Benedict’s test is a brick-red colored precipitate. KNUST Open Educational Resources, Benedict’s Test – Qualitative Test in Carbohydrates. Aldehydes give a positive result, and ketones give a negative result for Benedict’s test.

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