Laboratory Activity: Teacher Notes

Activity 1: Analysis of Sodium Chloride in Snack Food

Major Chemical Concept

Students will use the Mohr Chloride Titration method (see Pre-Laboratory Discussion Items 3 and 4) to determine the amount of sodium chloride in a snack food such as Fritos®


This activity is appropriate for all levels of chemistry classes.

Expected Student Background

Skills: Using a buret, pipet, and unit analysis calculations. Concepts: Solubility, averaging values of several trials in an analysis, using a "blank" in chemical analysis.


40-50 min, if snack filtrate is prepared ahead of time.


Read the Safety Considerations in the Student Version.

Materials (For 24 students working in pairs)


Consumables (see Advance Preparation)

Advance Preparation

  1. Preparing the snack filtrate: Weigh out 20.0 g of crushed Fritos® soak 24 hr in 600 mL distilled water; filter through thick cheese cloth, rinse and bring total volume to 600 mL in a graduated cylinder. The solution will be cloudy. Record exact volume. Use pH paper to test pH of filtrate. If pH is below 7.0 or above 10.0, adjust with 1 M NaOH or 0.5 M H2SO4, respectively. The filtrate should be stored in a refrigerator. To prevent mold, add a few crystals of thymol or a few drops of Lysol disinfectant. WORD OF WARNING: Pretzels are suitable, but potato chips and cheese-flavored snacks are difficult to filter.
  2. Solution preparation:
    1. AgNO3 solution, 0.0141 M: Dissolve 2.4 g AgNO3 (dried overnight at 140 degrees Celsius) in chloride-free water and dilute to 1.00 L. Store in a brown bottle.
    2. K2CrO4 indicator solution: Dissolve 10 g K2CrO4 in a little distilled water. Add AgNO3 solution until a definite red precipitate is formed. Allow to stand 18-24 hr, filter, and dilute filtrate to 200 mL with distilled water. Put into dropper bottles.