Preparation of Reagents

Preparation of Reagents

Benedict’s Reagent

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Requirements (Chemicals):

1. Copper(II) sulfate pentahydrate (CuSO₄·5H₂O) – 17.3 g
2. Sodium carbonate (Na₂CO₃) – 100 g (anhydrous)
3. Sodium citrate (C₆H₅Na₃O₇·2H₂O) – 173 g
4. Distilled water – To make 1 liter

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Theory Behind Components:

1. Copper(II) sulfate provides the Cu²⁺ ions (blue color), which are reduced by reducing sugars.
2. Sodium carbonate creates an alkaline medium, necessary for the redox reaction.
3. Sodium citrate acts as a complexing agent, preventing precipitation of copper carbonate in alkaline solution by keeping Cu²⁺ in solution.

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Procedure:

1. Dissolve sodium carbonate (100 g) and sodium citrate (173 g) in about 800 mL of distilled water in a beaker or volumetric flask. Stir well until fully dissolved.

2. In a separate container, dissolve copper(II) sulfate pentahydrate (17.3 g) in about 100 mL of distilled water.

3. Slowly add the copper sulfate solution to the carbonate-citrate solution with constant stirring.

4. Once completely mixed, make up the volume to 1 liter with distilled water.

5. Store the reagent in a dark bottle (amber glass) and label properly. The reagent is stable for several months at room temperature.

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Storage:

1. Store in a cool, dark place.
2. Always shake well before use.
3. Discard if any precipitate forms or color fades significantly.

Preparation of Molisch’s Reagent

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Requirements (Chemicals):

1. α-Naphthol (alpha-naphthol) – 5 g
2. Ethanol (95% or absolute alcohol) – 100 mL

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Procedure:

1. Take a clean, dry amber glass bottle.

2. Dissolve 5 grams of α-naphthol in 100 mL of ethanol.

3. Shake well until the α-naphthol is completely dissolved.

4. Label the bottle: “Molisch’s Reagent – 5% α-Naphthol in Ethanol”.

5. Store the reagent in a cool, dark place, tightly stoppered.

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Note:

1. Use pure α-naphthol for best results.
2. The reagent is flammable due to ethanol – handle with care.
3. Store in an amber bottle to prevent degradation from light exposure.