Titration of Cola

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The CCLI Initiative
Computers in Chemistry Laboratory Instruction

LEARNING OBJECTIVES The objective of this laboratory experiment is to determine the molar concentration of phosphoric acid in a cola product. BACKGROUND Titration is an analytical technique used to find the concentration of a known volume of unknown substance by adding a known concentration of a known substance. As the unknown and known substance react, we look for a "telltale" indication that the reaction is complete, which allows us to determine the concentration of the unknown. The most common type of titration is known as an acid-base titration. In an acid-base titration, we start with a known amount (usually a volume) of an unknown concentration of acid and add to it known amounts of a known concentration of base (or vice versa). For our purposes, the equivalence point is the most crucial point in the titration. It is the point during the titration where the moles of base added will equal the moles of acid in the unknown solution (or vice versa). Since the volume of base added can be read from the buret at this point and the concentration of the base and the volume of the acid are also known, the concentration of the unknown acid solution can be determined. There are a number of ways to determine the equivalence point, two of which can be used in this experiment. The first is by measuring the pH of the solution as you add base to the acid. There is a dramatic increase in the pH of the solution at the equivalence point(s) as shown in Figure 1 on the following page. A second way to detect the equivalence point is by using a thermometric method. Because acid-base reactions are exothermic, the solution being titrated warms as base is added. At the equivalence point, there is no further acid-base neutralization reaction and solution warming decreases or ceases abruptly. If you have a precise enough temperature measuring device, this abrupt change in...
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