DETERMINING THE CONCENTRATION OF CITRIC ACID IN A SOFT DRINK USING ACID/BASE TITRATION
Copyright: Department of Chemistry, University of Idaho, Moscow, ID 83844-2343; 2007. INTRODUCTION
The acid content of many foods and beverages contributes significantly to their taste. Soft drinks often contain varying quantities of several acids, which give sodas their tart flavor. In cola products, these acids are predominantly carbonic acid (from the carbonated water) and phosphoric acid. In sodas such as Squirt and 7-Up, the acids are carbonic acid and citric acid. Acids can be classified as monoprotic, diprotic, triprotic, etc.: a monoprotic acid has one proton that can undergo a reaction with a base, a diprotic acid has two such protons, and a triprotic acid has three. Shown below are examples of each type of acid undergoing a reaction with sodium hydroxide. Monoprotic: HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)
Diprotic: H2SO4(aq) + 2 NaOH(aq) → 2 H2O(l) + Na2SO4(aq)
Triprotic: H3PO4(aq) + 3 NaOH(aq) → 3 H2O(l) + Na3PO4(aq)
Any acid that has more than one proton that undergoes a reaction with a base is called a polyprotic acid. Citric acid is a weak, polyprotic acid that undergoes the following reaction with sodium hydroxide. H3C6H5O7(aq) + 3 NaOH(aq) → 3 H2O(l) + Na3C6H5O7(aq)
In this experiment you will be performing a titration to determine the concentration of citric acid in a soft drink. Prior to the titration, the majority of the carbonic acid was removed by allowing the soft drink to go flat so we do not have to take it into consideration.
A buret is used in a titration to dispense measured increments of one solution into a known volume of another solution. Careful technique will allow you to detect the point where the reaction is complete; in this case, when all of the citric acid has been reacted with the base. The technique of titration can be applied to other types of reactions such as oxidation-reduction, precipitation, complexation and other acid-base...
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