Reagent: Benedict's solution (Blue).
Method: Add reagent to the sample and heat in a water bath (approx. 80°C - 100°C) for 5 minutes.
Principle: Reducing sugars reduce soluble blue copper(II) ions to insoluble red copper(I) oxide precipitate.
Result Spectrum: Blue (None) Green/Yellow (Trace) Orange (Moderate) Brick Red (High). This is a semi-quantitative test.
Reagent: Iodine solution (Yellow-brown).
Method: Add drops directly to the sample at room temperature.
Result: A color change to Blue-Black indicates the presence of starch.
Chemical Hazards: Biuret solution contains sodium hydroxide (corrosive) and copper sulfate (irritant). Eye protection is mandatory.
Flammability: Ethanol is highly flammable. The lipid test must be performed away from open Bunsen burner flames.
Thermal Hazards: The Benedict's test requires a water bath near boiling point. Care must be taken to avoid scalding.
General Hygiene: Wash hands immediately if chemicals contact skin; never taste laboratory samples.
Color Descriptions: Be precise. Use "Brick Red" for high glucose, not just "Red". Use "Blue-Black" for starch, not "Dark Blue".
Negative Results: Always state the starting color if the result is negative (e.g., "Remains blue" is better than "No change").
Method Sequence: For lipids, the order is critical: Ethanol then Water. Mixing them all at once often fails to produce a clear emulsion.
Heat Requirement: If a question asks for a glucose test description, omitting the "heat" step usually results in zero marks for the method.
