A positive Seliwanoff's test is obtained with? A] Glucose B] Fructose C] Galactose D] Mannose

A positive Seliwanoff’s test is obtained with Fructose.

Seliwanoff’s test is a compound test which separates aldose and ketose sugars. This test is much like Bial’s test. his test depends on the rule that, when heated, ketones are more quickly dried out than aldoses. It is named after Theodor Seliwanoff, the scientific expert, who performed the test.

Two important things required to perform the experiment are

  • Seliwanoff’s Reagent.
  • The material in which you are trying to test the presence of Keto sugar.

To prepare this reagent you will need HCL, distilled water, and resorcinol. Once you have these three things you are ready to prepare the reagent for the test.

First add 34ml of hydrochloric acid in 68 ml of distilled water and after that, add 0.15 ml of resorcinol. Reagent is ready to perform the experiment.

Principle: Seliwanoff Test is a test to separate keto sugars structure Aldo sugars. Keto sugars get dried out in the nearness of concentrated acids to yield furfurals or their subsidiaries which react with resorcinol in Seliwanoff reagent to yield a cherry-red hue complex as the positive result. A cherry-red shading shows the nearness of ketohexoses. Ketopentoses yield blue-green series while aldoses and disaccharides give no shading change.

Procedure:

  1. Take a test tube and add 5 ml of Seliwanoff’s reagent in it. Make sure that the amount of reagent you are adding in the test tube doesn’t exceed 5 ml and measure it before pouring it.
  2. Now the material which is to be tested, pick it up, measure 1 ml of it and pour it down in the test tube.
  3. The third step should be to heat the solution using boiling water. Boil the solution in boiling water for 5 minutes and then wait on for the results. Now note down the colour change obtained which gives you the final result.

Result:

After the test is being performed, you will observe the color changes in the solution. If the color turns to Red, then this means that your results are positive and keto sugar is present inside the solution.

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