Lab_9_-_Acid___Base_Chemistry_1_ - Lab 9: Acid/Base...

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Lab 9: Acid/Base chemistry and Buffer Capacity Laboratory Goals In this lab, you will: Demonstrate your proficiency at titration by analyzing a sample of an organic acid Examine the acid/base characteristics of an organic acid Determine the concentration of an organic acid Safety Notes You will be using acid and base solutions; show appropriate caution. Introduction You are the on-site quality control chemist at the commercial entity, Briggs Sof Drinks Company. One of the company’s newly developed products is the MaliBlast High Energy drink, advertised as a healthy energy drink. The secret recipe of the energy drink is: Fruit juice (30mM malic acid) Water Natural and artificial flavorings Caffeine Artificial coloring The drink is prepared by thoroughly combining the ingredients, and clarifying the mixture by filtration (to removed suspended particles). The pH is adjusted to 4.5 to give the drinks a nice sour taste. There have been some concerns that the supply of fruit juice used may be tainted by a bacterial contamination. The suspected bacteria is known to be a malolactic fermenter. This organism will ferment malic acid into lactic acid with the production of carbon dioxide. Your company is required to keep the pH 4.5 or lower to prevent possible growth of dangerous bacteria like Clostridium botulinum from growing either during production or storage. You will have 3 product samples to consider that have been randomly sampled from the production line. Your job is to determine if any of the samples show evidence of the tainted fruit juice source. You will be using your knowledge of acid base reactions and equilibrium constants to solve this puzzle. Titration Curves A titration curve is a plot of pH vs. volume of base added, V (see Figure 1). If you are titrating a base into an acid, when you begin the solution should have a low pH, indicating an acidic solution. As you add base, the acid gets neutralized and the amount of free H + declines; since pH = -log[H + ], the pH increases. Around the equivalence point, the pH rises sharply for small additions of base, and after the equivalence point, the pH resumes its slow rise as you make the solution more basic by further additions of base. You may observe more than 1 inflection point for an acid with more than 1 acidic proton.
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Figure 1: Sample titration plot showing equivalent point and determination of pK a Taken form Wentworth and Dobie-Galuska You may use one of two methods to determine when all the acid has been reacted with the base. You may observe the point where there is a final sudden change in pH. Half-way in that jump is the equivalence point (V e ) and shown in figure 1. The is the amount of base which reacts with the acid. Alternately, you may use the second-derivative curve.
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This note was uploaded on 04/15/2009 for the course LB 171L taught by Professor All during the Spring '08 term at Michigan State University.

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Lab_9_-_Acid___Base_Chemistry_1_ - Lab 9: Acid/Base...

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