The Effect of Ph on a Food Preservative

Introduction:

The purpose of the first part of the lab was to test whether or not a food preservative, sodium benzoate, forms benzoic acid when placed into a simulated stomach acid. According to the lab manual; even though benzoic acid is effective as a food preservative, sodium benzoate is the more popular choice as it is more soluble in water thus making it easier to blend into “water-containing food products.” Below is the chemical formula indicating the reaction between sodium benzoate and hydrochloric acid to produce benzoic acid and sodium chloride.

C6H5COONa + HCL → C6H5COOH + NaCl

For the second part of the experiment, the density of an unknown liquid was determined by using a graphical method. A material's density is defined as its mass per unit volume.

Discussion:

Part A: This experiment started with a clear solution of sodium benzoate and HCl was added to it, ultimately producing benzoic acid. First approximately 2 grams of sodium benzoate was weighed, then it was dissolved in water, causing it to disassociate into ions. Next, 3M of HCl were added drop wise to the solution until it reached a pH of 2, thus introducing the hydronium ion. This addition caused a white, solid benzoic acid to precipitate out of the solution. A vacuum filtration system was used to separate the solid from the liquid. By using several chemicals, gas, distilled water, ice, and heat; the precipitate that formed was then filtered and weighed. The importance of precision the method of keeping the result at a low error margin was quantitative transferred. The Vacuum filtration was applied to the method to allow us to isolate a solid from a liquid-solid mixture and removing solid impurities from a relative large quantity of liquid.

Once the final product was dried, the mass of the benzoic acid produced was 1.62 grams, with a percentage yield of 95.29%, with a theoretical value of 1.70 grams of benzoic acid. Although there was not a 100% yield for the experiment, that is common as human errors could have occurred during several processes. For example, one error, which caused a lower percentage yield, could have been due to the transferal from the beaker with the solution into the vacuum filter. Not the entire product was removed from the beaker thus lowering the final mass. Another potential error could have occurred during the weighing process: the amount of grams of sodium benzoate could have fluctuated so the calculated theoretical was higher than the actual amount of reactant used in the experiment. One other error could have been due to the pH levels; if the pH was higher than expected, greater than 2, the sodium benzoate did not fully react with the hydrochloric acid. Since the two chemicals did not fully react with one another, there could have been leftover reactant, which resulted in lower amounts of product formed.