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Effect of pH on Food Preservative

By mbenner Oct 29, 2013 489 Words
Michael Pitner
Chem 253- TA: Gia Hoang
Lab 1: Effect of pH on a Food Preservative
9-1-2011

Purpose
The purpose of this lab was to determine if a new substance forms when sodium benzoate is placed in a simulated stomach acid.

Theory
Benzoic acid can be found in a wide variety of plants. It is used as a natural preservative in many foods. Sodium benzoate, the salt of benzoic acid, has become a more popular choice as a food preservative because it is more soluble in water than benzoic acid. Many food items found today are preserved with sodium benzoate.

Reaction
Reaction: sodium benzoate + hydrochloric acid  benzoic acid + sodium chloride Amounts: 2.00 g 5.0 mL 3M

+ HCl → + NaCl

Yield Calculations:

Because there are less moles of sodium benzoate, it is the limiting reagent.

The theoretical yield of Benzoic Acid is 1.706 g.

The actual yield of Benzoic Acid is .754 g.

The percent yield of this experiment is:

Methods/Procedures

The experiment was done according to the textbook as found on pages 40-47 using the Standard Scale directions. Safety issues that were accounted for were that both sodium benzoate and benzoic acid are irritants. Safety goggles were worn and care was taken to ensure that none spilled onto skin or clothes. Hydrochloric acid is a strong acid and is very corrosive. Care was taken not to get any on clothes, skin, or into eyes.

Observations/Results

After the sodium benzoate was mixed into the water and the HCl was added, the solution underwent a color change from a clear substance to a white substance. Also, a precipitate began to form. This precipitate was a dry, white solid with a mass of .754 g.

Discussion/Conclusion

My results seem to be a little askew. While the experiment was done correctly and the calculations correct, not enough of the product was transferred from the flask to the filter to the vial. Had a greater amount have been transferred, the results would have reflected a well done experiment. In the end, pH affected the food preservative sodium benzoate by turning it into benzoic acid under stomach conditions.

Exercises

1. There were a couple differences between sodium benzoate and benzoic acid that were observed. The first was a color change in the solution as HCl was added to sodium benzoate. The second change was that a solid precipitate was formed after mixing in HCl to the sodium benzoate.

2. In the reaction between sodium benzoate and hydrochloric acid that yields benzoic acid and sodium chloride, the stronger acid is hydrochloric acid whereas the weaker acid is benzoic acid. The stronger base is sodium benzoate and the weaker base is sodium chloride.

4. a. If aqueous NaOH were added to the solution to raise the pH, sodium benzoate and water would form. Sodium chloride would dissociate and the hydrogen from benzoic acid would attach to the OH to form water and the positive Na ion would bond to the benzoate anion. b.

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