Chem 112

Experiment 2 Acetic Acid Content of Vinegar By Kelsey Huber Chem 112L-01-George Gachumi September 19, 2011 Lab partners: Danielle Antes, Alex Ogren, Vanessa Kellems In this experiment acetic acid will be titrated with sodium hydroxide. As the sodium hydroxide is titrated into the acetic acid it is measured by pH. The sodium hydroxide is added into the acetic solution in small increments using a burette. The concentration of acetic acid averages at 0. 9±1. 5M and the known value of the acetic acid is 0. 833M.
The percent error of the experiment averages at 0. 66%. Possible errors could include incorrect measurements of sodium hydroxide and/or acetic acid. Background: Titration is when one solution is slowly added to another solution so that the reaction between the two can be accurately recorded or measured. For example, when a base is slowly added to an acid the equivalence point should be neutral. Methods of titration are even used in the food industry to express the oil and fat contents in different products.
For example, titration is used in the cheese and the wine business to test if the product is ready for consumption. Procedure: Hirko, R. Chemistry 112L General Chemistry I Laboratory, 5th ed. ; bluedoor: Eden Prairie, MN, 2011; Experiment 2. Results: Graph A. 1 shows the second derivative used to find the volume of NaOH to equivalence point which equals 8. 02 ml. Graph A. 2 shows the titration curve of the pH versus the volume of the solution. Graph A. 1 Graph A. 2

Discussion: The titration of sodium hydroxide to acetic acid eventually produced a dark pink solution. The equivalence point of this solution is a weak acid. The acetic acid molarity of commercial vinegar varied slightly in the three trials. In trial one the vinegar molarity was 0. 173 M, in trial two it was 1. 061 M, and in trial three it was 1. 322 M. The concentration of acetic acid was calculated at 0. 9±1. 5 M, by taking the average of three trials. This is within 0. 067 M of the known value which is 0. 833 M.
By inspection of the titration curves there could be a difference based on the exact amount of sodium hydroxide being dropped from the burette into the acetic acid solution. At the equivalence point the pH is not seven because acetic acid is a weak acid and it is being mixed with a strong base, sodium hydroxide. The indicator turned red when it reached the equivalence point. Phenolphthalein was a good indicator for the titration of a weak acid with a strong base because it was the solution that caused the red color as the sodium hydroxide and acetic acid reached an equivalence point.
Phenolphthalein would however not be a good indicator for titration of a weak base with a strong acid because the phenolphthalein reacted with the sodium hydroxide to create the red color; it was not turning red as a result of the acetic acid. Inaccuracies in the determined concentration of sodium hydroxide to acetic acid can be attributed to possible measurement errors. Inaccurate measurements while adding the sodium hydroxide from the burette into the acetic acid throughout the three trials could result in various outcomes on the graphs effecting results such as the equivalence point and the titration curve.