Overview
This lecture covers biochemistry lab tests to identify starch, simple sugars, fats, proteins, and pH levels using various chemical reagents and equipment.
Starch Test with Iodine
- Iodine solution is used to test for the presence of starch.
- Mixing iodine with a starch solution results in a characteristic color change.
- Unknown samples are tested to determine which contains starch; a positive match shows the same color as the starch control.
Simple Sugar Test with Benedict’s Solution
- Benedict’s solution detects simple sugars like glucose.
- Mix 1 mL of each sample with Benedict’s solution and heat to 70°C.
- A color change after heating indicates the presence of reducing sugars.
- Identified which unknowns contained glucose by comparing color changes.
Fat Test with Paper (Oil Spot Test)
- Oil, water, and various samples are dropped on paper to test for fats.
- A translucent spot indicates the presence of fat/oil.
Protein Test with Biuret Reagent
- Biuret reagent is used to test for proteins.
- Albumin serves as the positive control.
- Add Biuret reagent to each sample; a color change indicates protein presence.
pH Testing with Indicators
- pH of unknowns is tested with pH paper strips and compared to color charts.
- Methyl orange and phenolphthalein are additional pH indicators used for color comparison.
- A portable pH meter is used for precise pH measurement.
Review of Results
- Compared results to controls for each test to identify which unknowns contained starch, sugar, fat, or protein.
- Noted which unknowns matched the controls in color or reaction.
Key Terms & Definitions
- Starch — a polysaccharide tested with iodine.
- Iodine Test — identifies starch by color change.
- Benedict’s Solution — detects reducing sugars like glucose with heat.
- Biuret Test — detects proteins by color change.
- Albumin — protein reference used as a control.
- Methyl Orange — pH indicator (acidic to neutral).
- Phenolphthalein — pH indicator (neutral to basic).
- pH Meter — device for measuring the hydrogen ion concentration of a solution.
Action Items / Next Steps
- Compare lab results to controls and document which unknowns test positive for each biomolecule.
- Complete any lab manual questions and submit observations.
- Review color chart comparisons for pH testing.