Laboratory Activity: Teacher Notes

Major Chemical Concept

The methods for extraction of milk components are based upon their chemical differences:

• Fats: Extraction from a polar emulsion with a nonpolar solvent.
• Proteins: Precipitation by denaturation.
• Water: Evaporation.
• Carbohydrates: By difference.

Level

For all levels of high school chemistry.

Expected Student Background

Students should be familiar with the properties of fats, proteins, and carbohydrates.

Time

Two 50-min periods. It is not necessary for the laboratory periods to be on consecutive days.

Safety

1. Read the Safety Considerations in the Student Version.
2. The nonpolar solvent is volatile and has hazardous fumes.

Materials (For 24 students working in pairs)

Part 1

Nonconsumables

• Balances
• 24 Graduated cylinders, 100-mL
• 12 Erlenmeyer flasks, 250-mL
• 12 Stoppers to fit flasks
• 12 Transfer pipets and bulbs (size appropriate for extracting in steps 100 mL aqueous layer from milk sample); alternately, separatory funnels
• 12 Beakers, 250-mL

Consumables

• Fresh whole milk, 1.2 L
• Nonpolar solvent, 1.2 L (see Advanced Preparation, Part 1)

Nonconsumables

• 12 Buchner funnels, suction flasks; alternatively, funnels, flutedfilter paper
• 12 Spatulas
• 12 Beakers, 250-mL
• 12 Watch glasses

Consumables

• Aqueous layer (from Part 1) in 250-mL beaker
• Vinegar, 1.2 L
• 12 Filter papers (to fit Buchner funnel)

Continued

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