Laboratory Activity 3: Teacher Notes
Continued
Part 4
Nonconsumables
- 12 Graduated cylinders, 10-mL
- 12 Evaporating dishes
- 12 Glass stirring rods
- 12 Beakers, 250-mL
- 12 Ringstands
- 12 Ring clamps
- 12 Wire mesh
- 12 Burners
Consumables
- Milk, 60 mL
- Boiling chips
Advance Preparation
Part 1
- Purchase fresh whole milk. (Lowfat milks do not work very well.) Check the label on the carton to see if the declared values match those given to students in the data table. Adjust accordingly.
- Use separatory funnels if they are available instead of the pipets in Part 1, Step 7.
- Possible nonpolar solvents include trichlorotrifluoroethane (TTE), hexane, cyclohexane, and dichloromethane. Consider the hazards and cost for using each solvent. NOTE: TTE is available as DuPont TF Solvent from dry-cleaning supply companies; this technical grade solvent is considerably less expensive than the higher-grade TTE found in some chemical supply catalogs. Mix equal amounts (1mL) of each nonpolar solvent and water to determine position of water layer.
Part 2 and 3
- A Buchner funnel and aspirator is ideal for the filtration of the protein. If not available, filter material through fluted filter paper to hasten filtration.
- If filter paper is used, remember to remove the filter paper containing the protein from all students' funnels for overnight drying at the close of the first day. Set them on paper towels to dry overnight. Try not to leave the protein sample in one large clump (low surface area retards drying). Spread the protein thinly on the filter paper with a spatula. Leave the appropriate beaker and filtrate next to each filter paper.
- Air drying will not remove all the water from the protein. However, the mass of the water remaining is not large enough to affect the students' results in any significant way. If desired, the protein could be given a final wash in ethanol to hasten drying.
- Only the casein fraction of the protein is removed during protein extraction. The whey proteins (Beta-lactoglobulin and Alpha-lactalbumin) are not precipitated. Thus it is incorrect to claim that this procedure measures "all" milk protein. However, since casein is the major protein in milk, student results will be quite acceptable.
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