Lab1: Effect of Ph on Food Preservatives
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 yield from the reaction. Also throughout the experiment, some basic laboratory operations such as measuring mass and volume, separating solids from liquids by vacuum filtration and drying solids are familiarized with.
Introduction
The reaction of sodium benzoate and hydrochloric acid is a typical phenomenon of hydrolysis reaction which conforms to the principles of acid-base chemistry and stoichiometry. In a typical hydrolysis reaction, when a salt dissolves in water, the salt dissociates to its constituent anions and cations (benzoate and sodium ions respectively). Also, when strong acids like hydrochloric acid dissolves in water, chloride ions and hydronium ions are formed. Hence in the reaction involving sodium benzoate and hydrochloric acid solution, in the presence of high concentration of hydronium ions, protons will be transferred from the strong acid H3O+ to the basic benzoate ion. This will yield benzoic acid, C6H5COOH which precipitates from the solution as it has a really poor solubility (0.34g/100ml). The fundamental reaction is sketched out below:
As can be seen from the difference in the pKa values, H3O+ is a much stronger acid than benzoic acid. So, the equilibrium of the reaction strongly favours its completion
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 yield from the reaction. Also throughout the experiment, some basic laboratory operations such as measuring mass and volume, separating solids from liquids by vacuum filtration and drying solids are familiarized with.
Introduction
The reaction of sodium benzoate and hydrochloric acid is a typical phenomenon of hydrolysis reaction which conforms to the principles of acid-base chemistry and stoichiometry. In a typical hydrolysis reaction, when a salt dissolves in water, the salt dissociates to its constituent anions and cations (benzoate and sodium ions respectively). Also, when strong acids like hydrochloric acid dissolves in water, chloride ions and hydronium ions are formed. Hence in the reaction involving sodium benzoate and hydrochloric acid solution, in the presence of high concentration of hydronium ions, protons will be transferred from the strong acid H3O+ to the basic benzoate ion. This will yield benzoic acid, C6H5COOH which precipitates from the solution as it has a really poor solubility (0.34g/100ml). The fundamental reaction is sketched out below:
As can be seen from the difference in the pKa values, H3O+ is a much stronger acid than benzoic acid. So, the equilibrium of the reaction strongly favours its completion