Determination of the Concentration of Acetic Acid in Vinegar

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Determination of the Concentration of Acetic Acid in Vinegar Lab Exercise 4
CHEM 1106

9/19/12

Purpose:
Standardize a sodium hydroxide solution using a primary standard acid. Determine the molarity and the percent by mass of acetic acid in vinegar by titration with the standardized sodium hydroxide solution. Introduction:

Vinegar is a dilute solution containing acetic acid. Since vinegar has a low pH, it can be titrated with a base. Titration is a method used in order to ascertain the amount of a constituent in a solution by measuring the volume of a known concentration of a reagent required to complete a reaction with it, typically using a burette. The equivalence point of a titration occurs when chemically equivalent amounts of acid and base are present. In this experiment, the equivalence point occurs when the moles of acid in the solution equals the moles of base added in the titration. A rapid change in pH with the small addition of acid or base is the indicator for acid-base equivalency. Using a pH meter and a graph of pH plotted versus the volume of base added, the equivalence point can be accurately found by finding the point that is in the middle of the vertical part of the curve. Once the equivalence point of the titration is known, the concentration of the sodium hydroxide can be determined. Sodium hydroxide is used to titrate vinegar so that the concentration of the vinegar is determined. The percentage of acetic acid in solution can be determined from the concentration of the vinegar.

Procedure:
Part A – Standardization of a Sodium Hydroxide Solution
1. Prepare 150 mL of approximately 0.5M sodium hydroxide solution from solid NaOH. The solution can be prepared in a beaker, it is not necessary to use a graduated cylinder or a volumetric flask because the NaOH solution will be standardized. 2. Weigh a 150-mL beaker and record the mass to the nearest 0.001 g. Add approximately 0.5 grams of potassium hydrogen phthalate...
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