Physical Separations
HOW MUCH FAT IS IN YOUR CHIPS?
Introduction
If you look on the back of any food package, you will see that the label breaks the nutritional content into
the categories such as carbohydrates, proteins, and fats, sodium, fiber, etc. The nutritional content is printed to help
you monitor and maintain a healthy diet. Other ingredients such as water, natural and artificial flavorings, dyes, and
preservatives typically do not affect the nutritional content.
Studies conducted by doctors and scientists show that Americans consume far more fats, sugars, and salt
than recommended for a healthy diet. In this experiment you will determine the amount of fat in different snack
chips. Snack chips are composed primarily of fat, carbohydrates, and salt (NaCl). Fats are nonpolar and dissolve in
nonpolar solvents. Carbohydrates have varying composition (sugar is polar and water soluble, grains contain
polymeric carbohydrates that are insoluble in essentially everything). Proteins are also insoluble in essentially
everything. Salt is very soluble in water. By selectively dissolving the fat and weighing the remains, you can
determine the mass percent fat in the chips.
Goal: To determine the mass percent fat in snack chips and compare the experimental value to the actual value
calculated from the snack bag.
Prelab:
1. What kind of snack chips do you have? ____________________________
2.
Look at your snack chip bag and record the mass per serving and the % Daily Value in the table below. Add
any nutritional categories of interest that are not already listed.
3.
Calculate the mass % of each serving that is fat, carbohydrates, and protein.
4.
Assuming that 1 g fat has about 9 Calories and 1 g carbohydrates or protein have about 4 Calories, calculate the
number of Calories from fat, carbohydrates, and protein in your chips.
Category
mass/ serving
% mass
Entire Serving
Cal/ serving
% Daily Value
-
Carbohydrates
Proteins
Fat
5.
Referring back to the introduction and following the theory of "like dissolves like," what will dissolve and what
will not if your chips are mixed with water? If the water is filtered, what will remain behind?
6.
What will dissolve if your chips are mixed with hexane (a nonpolar solvent)? What will remain behind if the
chips are filtered?
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How Much Fat is in Your Chips?
Physical Separations
Safety:
1. Always wear eye protection on the MCL.
2. DO NOT EAT THE CHIPS.
3. CAUTION: n-hexane is highly flammable.
Procedure:
1. Using the balance obtain a piece of snack chip that weighs approximately 1 g. Record the exact mass in your
data table.
2.
Grind the piece of snack chip into crumbs with the mortar and pestle.
3.
Add about 20 mL n-hexane to the mortar and continue grinding for one additional minute.
4.
Fold a piece of filter paper in half; then fold it in half again. Weigh the filter paper. Record the exact mass.
5.
Place the filter paper in the funnel with 3 of the folds on one side and one fold on the other side.
6.
Transfer the crushed chips to the filter paper in the funnel by following the procedures outlined in Figure 1.
A. Hold the funnel containing the filter paper over the 50 mL beaker and move the mortar right next to the
beaker.
B. Use the pipet to gently agitate the hexane/chip mixture. When the chips and hexane are well mixed,
carefully transfer the hexane/chip mixture to the funnel. Leave as few crumbs behind as possible. Allow
the n-hexane to filter through the funnel and into the beaker.
C. If chips are left in the mortar after transferring all the hexane to the funnel, transfer the filtered hexane in
the beaker back to mortar and repeat steps A and B.
7.
Holding the funnel upright, go to the vacuum station and place the funnel into the rubber sleeve on a filter
flask. (Figure 2)
8.
Press down on your funnel to hold it tightly in the rubber sleeve.
9.
Turn the stopcock to open it to your filter flask and the vacuum. This opens your sample to a vacuum that will
draw air through the filter paper and evaporate the remaining n-hexane, leaving dry potato chips.
10. Allow the pump to pull off the remaining n-hexane for about 2 minutes. The sample will get cold initially.
When it warms to room temperature again, the hexane is gone.
11. Close the stopcock and carefully remove your funnel.
12. Weigh the filter paper and chip remains. Record the mass in your data table.
13. If time permits, repeat this entire procedure and record the data under Measurement 2 in your data table.
Data Table
Measurement 1
Measurement 2
Mass of chip
Mass of filter paper
Mass of filter paper + chip after n-hexane wash
Mass of chip after n-hexane wash
Mass of fat
Mass % of fat in chip (Measured)
Mass % of fat in chip (from prelab)
% error in measurement
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How Much Fat is in Your Chips?
Physical Separations
Postlab
1. Using the measurements in your data table, calculate the mass of your chips after the n-hexane wash. Record
the value in your data table.
2.
Assuming the difference in the mass of your chips before and after the hexane wash is due exclusively to
removal of the fat, calculate the mass of fat in your chip sample. Record the value in your data table.
3.
Using your experimental data, calculate mass percent fat in the chips. Record the value in your data table.
4.
You now have experimental measurements (data table) and theoretical values (prelab) for the mass % fat in
your chips. Explain what we mean by experimental and the theoretical values.
5.
Calculate the percent error in your measurement. Record the value in your data table.
6.
What (besides fat) makes up the rest of your chip?
7.
Referring to your data table, fill in column 3 (experimental mass) of the table below. (Assume the chip contain
only fat and carbohydrates.)
Category
Cal/gram
experimental
mass/serving
Cal/serving
mass
(experimental)
(experimental)
Entire Chip
-
Fat
9.0
Carbohydrate
4.0
8.
Using the ratios of your experimental masses for your chip and the defined serving size from the chip package,
calculate the experimental mass (grams) of carbohydrates and fat per serving (column 4). (Assume the chip
contains only fat and carbohydrates)
9.
Calculate the experimental values for the total Calories in one serving of chips, the Calories from fat, and the
Calories from carbohydrates (column 5). Compare your experimental values to the actual values in your
prelab.
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How Much Fat is in Your Chips?