The purpose of this experiment was to investigate a competitor’s claim that the food preservative, sodium benzoate (C6H5COONa), made by Fresh Foods International (FFI), changed into a new substance in stomach acid. Stomach acid has a pH between 1 and 3 due to the hydrochloric acid content. Based on the net equation given in the book as well as the solubility of the product our hypothesis is that a new substance will form. Net reaction: C6H5COONa(aq) + HCl(aq) C6H5COOH(s) + NaCl(aq)
Upon completion of this experiment students will gain experience using common extraction techniques such as vacuum filtration, as well as familiarity with common calculations used in chemistry, such as mass measurements and percent yield.
Description of Procedure:
2.00 g of sodium benzoate was dissolved in 10.0 mL of H2O. 7.0 mL of HCl was added to the solution and a pH of 2 (similar to stomach acid) was reached. Upon addition of the HCl, a white precipitate formed.
The mixture was cooled in an ice bath until a temperature of 10 degrees Celsius was obtained to reduce solubility further. Using vacuum filtration the solid precipitate was extracted from the mixture. To allow the solid precipitate sufficient time to dry mass of the substance was obtained one week later and was found to be 1.59g. Trace amounts of the solid precipitate were lost during transfer as they stuck to the stir stick and beaker. Data, Calculations and results:
.007L * (3mol HCl)/L * (1mol C6H5COOH)/1mol HCl =0.0210 moles C6H5COOH 2.00g C6H5COONa * (1mol C6H5COONa)/(144.1g)* (1mol C6H5COOH)/(1 mol C6H5COONa) =0.0139 moles C6H5COOH Limiting Reactant: C6H5COONa
Theoretical Yield: 0.0139 mol C6H5COOH*122.1g/ mol C6H5COOH = 1.70 g mol C6H5COOH mol C6H5COOH Actual Yield: 1.59g C6H5COOH
Percent Yield: (1.59g/1.70g)*100 = 93.5%
Based on the net equation listed in the Multi-scale Operational Organic Chemistry textbook for this experiment, the solid precipitate is benzoic acid (C6H5COOH). 93.5% yield was obtained as a result of the procedures performed. As noted above in the description of the procedure, trace amounts of the white precipitate were lost during transfer.
The yield collected as well as the observed white precipitate that formed support the hypothesis that a new substance would form. As for the claims by a competitor that it could somehow be harmful, further testing would need to be conducted. However, it was stated in the section labeled “Sodium Benzoate as a Food Preservative” that benzoic acid was also a food preservative, although less commonly used as it is relatively insoluble in water containing food products. Exercises 1,2,4 &5
1)One property that differs in sodium benzoate and benzoic acid is their solubility in an aqueous solution. Sodium benzoate is more soluble and benzoic acid is relatively insoluble. This difference was observed when benzoic acid precipitated out of solution upon addition of HCl. 2)C6H5COO- + H3O+ C6H5OOH + H2O
3)4 a ) If the pH of the system is raised by adding NaOH the C6H5COOH will disassociate and reform more of the reactant C6H5COONa. C6H5COOH + NaOH C6H5COONa + H2O
C6H5COONa(aq) + HCl(aq) C6H5COOH(s) + NaCl(aq)
Le Chatelier’s Principle states that when a chemical system at equilibrium is disturbed it will shift in the direction that minimizes the disturbance. If more products are added the system will shift to the left creating more reactant and vice versa. Adding NaOH is essentially the same as adding more products. The system would therefor shift toward the left, resulting in more of the reactant being produced.
b) C6H5COOH + OH- C6H5COO- + H2O
5)You would make oxalic acid, however, you would not be able to use filtration to obtain it as it is more soluble than sodium oxalate. So no, a different type of extraction would need to be performed. Na2C2O4 + HCl H2C2O4 + NaCl
Cite this Effect of pH ona food preservative
Effect of pH ona food preservative. (2016, Jun 24). Retrieved from https://graduateway.com/effect-of-ph-ona-food-preservative/