Lab1: Effect of Ph on Food Preservatives Essay

1362 Words Jun 18th, 2013 6 Pages
Lab 1: Effect of pH on sodium benzoate, a food preservative

Sheikh M Zakaria

Person no. 36295651

TA: Synthia Gratia

Date of Submission: 05/29/13

Abstract Sodium Benzoate is a common food preservative used in food products such as jams and jellies, soft drinks, pickles, condiments etc and in tinned products in the market. This experiment aimed to determine whether benzoic acid is formed from it’s superior soluble form sodium benzoate in stomach acid, which is simulated by HCl (pH=2). It has been seen that at a low optimum pH, i.e. in the presence of sufficient hydrochloric acid, sufficient benzoic acid is yielded. The percentage yield is determined from the calculations of the theoretical (stoichiometric) calculations and the actual
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A 90% yield suggests that all the basic operations were carried out as neatly and carefully as possible and measures taken to minimize obvious errors which could take place while performing the experiments. All in all, the experiment provided a practical evidence of the theory behind the hydrolysis of sodium benzoate and percentage yield of it’s product.

References 1. Multiscale Operational Organic Chemistry (4th edition) pg-4,5 and 7 for citations 1,3 and 4. 2. http://www.grossmont.net/tomolmstead/Chem%20231%20Spring%202013/Expt%201%20Lab%20Report.pdf for citation 2
Post lab exercises
Q. Your observations should reveal a difference in at least one property between sodium benzoate and benzoic acid. What property was that and what observation will reveal the difference?
Answer: The solubility of sodium benzoate and benzoic acid makes a major difference in identifying between these two compounds in the reactions. Benzoic acid is sparingly soluble in water (0.34g/100ml) while sodium benzoate readily dissolves in water (61.2g/100ml). So, if we take these two compounds and dissolve them in water in separate test tubes, sodium benzoate will form a clear solution while benzoic acid won’t dissolve and seen as a precipitate.
Q. When you lower the pH of a solution of sodium benzoate a ppt forms. What will happen if you raise the pH after the reaction by adding aqueous NaOH and why?
Answer:

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