1. Uji Fehling - Uji Daya Mereduksi

Introduction

This tutorial will guide you through the process of performing the Fehling test, a chemical test used to identify reducing sugars based on their ability to reduce copper ions from Cu2+ to Cu+. The result of this reaction is the formation of a colored precipitate, which can vary in color depending on the concentration of carbohydrates present in the sample. Understanding this test is essential in fields like biochemistry and food science.

Step 1: Prepare the Fehling Reagents

• Gather the necessary chemicals:
  • Fehling's Solution A: Copper(II) sulfate solution.
  • Fehling's Solution B: A solution of potassium sodium tartrate and sodium hydroxide.
• Mix equal volumes of Solutions A and B just before conducting the test. This creates the active reagent.

Step 2: Prepare the Sample

• Take the sample you wish to test, which could be a solution containing reducing sugars.
• If using solid samples, dissolve the appropriate amount in distilled water to create a clear solution.

Step 3: Conduct the Test

• In a test tube, add 1-2 mL of the prepared Fehling's reagent.
• Add 1-2 mL of your sample solution to the test tube.
• Heat the mixture gently in a boiling water bath for about 5-10 minutes.

Step 4: Observe the Reaction

• After heating, observe the color change in the solution. The possible outcomes are:
  • No color change indicates no reducing sugars present.
  • A green precipitate suggests a low concentration of reducing sugars.
  • A yellow-orange precipitate indicates a moderate concentration.
  • A brick-red precipitate signifies a high concentration of reducing sugars.

Practical Tips

• Ensure the solutions are freshly prepared for accurate results.
• Use a color chart to help determine the concentration of reducing sugars based on the color of the precipitate.
• Be cautious when heating the test tube to avoid splashes or burns.

Common Pitfalls to Avoid

• Avoid using acidic solutions, as they can interfere with the reaction.
• Ensure that the reagents are mixed well before adding the sample; improper mixing can lead to inaccurate results.

Conclusion

The Fehling test is a simple yet effective method to detect reducing sugars in various samples. By following the outlined steps and observing the color changes, you can determine the concentration of carbohydrates present. For further exploration, consider testing different types of carbohydrates or comparing results with other reducing sugar tests.