Research laboratory 1: Effect of pH upon sodium benzoate, a foodstuff preservative

Sheikh M Zakaria

Person no . 36295651

TAG: Synthia Gratia

Date of Submission: 05/29/13


Sodium Benzoate is a common meals preservative utilized in food products including jams and jellies, soft drinks, pickles, condiments etc in addition to tinned goods in the market. This experiment aimed to determine whether benzoic acid is formed by it's superior soluble contact form sodium benzoate in stomach acid, which is controlled by HCl (pH=2). It has been seen that at a low optimum ph level, i. electronic. in the occurrence of satisfactory hydrochloric chemical p, sufficient benzoic acid is definitely yielded. The percentage yield is decided from the computations of the assumptive (stoichiometric) computations and the actual yield from your reaction. Likewise throughout the research, some basic clinical operations including measuring mass and volume level, separating hues from fluids by vacuum filtration and drying hues are familiarized with.


The reaction of sodium benzoate and hydrochloric acid is a standard phenomenon of hydrolysis response which conforms to the principles of acid-base chemistry and stoichiometry. Within a typical hydrolysis reaction, each time a salt dissolves in drinking water, the salt dissociates to their constituent anions and cations (benzoate and sodium ions respectively). Likewise, when solid acids just like hydrochloric chemical p dissolves in water, chloride ions and hydronium ions are produced. Hence inside the reaction concerning sodium benzoate and hydrochloric acid answer, in the existence of high focus of hydronium ions, protons will be moved from the solid acid H3O+ to the basic benzoate ion. This will yield benzoic acidity, C6H5COOH which precipitates in the solution mainly because it has a actually poor solubility (0. 34g/100ml). The fundamental response is drew out below: As can be seen from the difference in the pKa values, H3O+ is a stronger acid than benzoic acid. So , the equilibrium with the reaction firmly favours their completion thus hydrochloric acidity which ideally simulates the acidic circumstances of the abdomen, does convert benzoate to benzoic acid solution.


Throughout the research laboratory safety eye protection, protective gloves and aprons were donned while carrying out the trials. While copying the HCl to the effect vial in the student bonnet, the head must never become inside the glass hood while vapour breathing can cause choking hazard and irritations. Also the hosepipes were carefully plugged in and out of the filter flask to stop breakage or perhaps tipping with the Hirsh funnel.

Trial and error

For this try things out and standard operations, arranged Pasteur pipettes, a 5ml conical response vial, view glass, mixing rod, digital balance, tiny test pipe, Hirsh funnel, filter flask and filtering paper are used. The procedure in this experiment shows up on page 7 of the laboratory manual, Multiscale Organic Biochemistry and biology (4th custom made UB edition)3.


Table: weight, volume level and percentage yield of benzoic acidity

Mass of sodium benzoate| 0. 42g

Volume of water| 3ml

Amount of hydrochloric acid| 1ml

Actual yield of benzoic acid| 0. 32g

Theoretical deliver of benzoic acid| zero. 3559g

Percentage yield of benzoic acid| 89. 91%

The assumptive mass of benzoic chemical p can be determined by the subsequent equation, given the molecular weights of sodium benzoate and benzoic acid (144. 1 g/mol and 122. 1 g/mol respectively) plus the reaction is usually 1: one particular C6H5COONa & HClC6H5COOH + NaCl

Assumptive yield of benzoic acid= 0. 42144. 1x 122. 1

The formula can be split up to derivation of the skin moles of benzoate which is zero. 42/144. one particular This is also equal to the moles of benzoic acid due to the one particular: 1 response stoichiometry. Therefore using mass= moles back button molecular pounds formula, the theoretical yield is derived. The proportion yield can be calculated using the equation

Percentage yield=( Actual yieldTheoretical yield by 100 ) %


As the main objective of this experiment was going to find...


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