I.Title: Acid-Base Titrations AP Chemistry Laboratory #6
II.Purpose: The purpose of this experiment is to standardize a sodium hydroxide solution and use the standard solution to titrate an unknown solid acid. The equivalent mass of the solid acid will be determined from the volume of sodium hydroxide added at the equivalence point. The equilibrium constant, Ks, of the solid acid will be calculated from the titration curve obtained by plotting the pH of the solution versus the volume of sodium hydroxide added. III.Background Information: Volumetric analysis is the use of volume measurements to analyze an unknown; a method of this is titration. Titration is most often used to analyze the amount of acid or base in a sample or solution in acid-base chemistry. In a titration experiment, a known volume of an acid solution would be “titrated” by slowly adding dropwise a standard solution, whose concentration is accurately known, of a strong base. The titrant reacts with and consumes the acid via a neutralization reaction. The point at which stoichiometric amounts of the acid and base have combined is the equivalence point. An example of this is shown in the equation: HCl(aq)+NaOH(aq)NaCl(aq)+H2O(l). The number of moles is given by knowing the exact concentration and volume added of the titrant. The latter, in turn, is related by stoichiometry to the number of moles of acid initially present in the unknown. To detect the equivalence point, indicators are usually added to acid-base titrations. The point at which the indicator changes color and signals the equivalence point has been reached is the endpoint of the titration. In the equation above the pH of the solution would be acidic before the equivalence point and basic after the equivalence point. The pH should be exactly 7 at the equivalence point, corresponding to the neutral products. If and indicator changes color around pH of 7 it is suitable for the titration of a strong acid with a...
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