Laboratory Activity: Teacher Notes

Answers to Implications and Applications

1. The National Research Council has defined an "adequate and safe" level of sodium as between 1000 and 3300 mg daily. Some physicians feel that this is too high and should be much lower, around 220 mg per day.
2. Answers will vary (see Assessing Laboratory Learning, Question 2, for a sample calculation).
3. Monitor the amount of salt in the diet.

1. Make sure that students have calculated their analytical data correctly and averaged their results. Put class values on the board for comparison and discussion.
2. Assist students in calculating mg NaCl in the entire Fritos® package. Food values are given as "mg Sodium," not "mg sodium chloride." Show students how to convert mg NaCl to mg Na.

   By ratio: (molar mass NaCl)/(molar mass Na) = mg NaCl/mg Na

   Unit Analysis: mg Na x (molar mass NaCl)/(molar mass Na) = mg NaCl

3. Discuss discrepancies between the stated value and the experimental results.
4. Ask teams of students to make an estimation of one person's daily intake of sodium, using information from library sources such as Composition of Foods, (U.S. Department of Agriculture, 1979).

1. The Mohr Chloride analysis can be used for pretzels, potato chips, and other salty snack foods.
2. Analyze tap water, bottled spring water, and pond or stream water for chloride content.

Assessing Laboratory Learning

1. When a sample of pretzels was analyzed by the Mohr chloride method, the following data was obtained:
   • Average mL for blank: 0.2 mL
   • Average mL for sample: 13.5 mL
   • Mass of pretzels used: 10.0 g
   • Total filtrate volume: 300.0 mL
   • Calculate the mg NaCl and the mg Na in a 1 ounce (28.4 g) serving of these pretzels.

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