The principal component of vinegar is acetic acid- HC2H3O2, and also a little bit of water. While analyzing vinegar and the percent composition of acetic acid in it, an acid/base reaction was performed by adding NaOH, a base, to vinegar, the acid. NaOH was added in small amounts at a time to a beaker containing 5.00 mL of vinegar and 20.0 mL of deionized water.
The concept of titration in this lab was to determine the concentration of acetic acid in vinegar by adding a base to the solution until the mixture was basic. The purpose of this lab was to first determine the pH of different household items and to then determine the concentration of acetic acid in vinegar.
Table 1: pH of Household Items
|Apple Cider Vinegar
Table 2: Titration Results from adding NaOH to Distilled Vinegar
|mL of NaOH added at equivalence
|Concentration of Vinegar
|Percent by weight of vinegar at equivalence
|.66 M HC2H3O2
Example of a Titration curve:
In part one of the lab, the pH of random household chemicals was determined. Lemon juice, both distilled and apple cider vinegar, and dish soap were all very acidic, each having a pH of less than 3. The more basic chemicals consisted of baking soda, Ammonia, and 409, each having a pH of greater than 8. It seemed that the majority of the cleaning chemicals tended to be basic, with an exception of dish soap. The edible chemicals were all acidic.
In part two, vinegar was analyzed to determine the concentration of acetic acid in it by slowly adding a base to the vinegar and water mixture and recording when it reached its equivalence point. To do so, a pH electrode was placed into a 100 mL beaker along with 5.00 mL of vinegar and 20.0 mL of deionized water, and the initial pH was recorded.
Each group then added 3 drops of pH indicator to visually display when the solution became basic. The pH electrode was placed into the solution each time after a small amount of NaOH was added to record the pH of the solution and make the graph on LoggerPro. Each group continued to add small amounts of the base, NaOH, until the pH was finished rapidly changing.
The first derivative was found for each value of NaOH added, and the largest derivative displayed the equivalence point. For trial 3, the pH was changing with respect to the volume at 10.48. The concept of titration is to calculate the concentration of an unknown solution (acetic acid in vinegar) by adding a measured amount of a solution (NaOH) of unknown concentration to a known volume of a second solution (vinegar and deionized water) until the reaction is complete, at a pH of around 7.
Distilled vinegar was used in the titration portion of the lab. In trial 3, it was found that when 22.3 mL of NaOH was added to the vinegar and water solution, the equivalence point was reached at a pH of about 9—9.17 to be exact. The concentration of acetic acid in vinegar was 0.66 M, and 4.0% by weight of vinegar. The actual results met with the expected results, having to add a little more of the base to the acid solution to make it neutral.
A likely source of error could have been made by not accurately adding the right amount of vinegar and deionized water to the beaker, which would throw off the actual amount of NaOH required to reach the equivalence point. Another probable source of error was most likely made by not adding the exact correct amount of NaOH, hence recording the wrong data into LoggerPro, resulting in an incorrect equivalence point.
The final source of error was made by not recording the mL of NaOH added to the solution and the resulting pH values for trials 1 and 2. Only recording results for Trial 3 resulted in not having a strong, defined conclusion to the initial objective of finding the concentration of acetic acid in vinegar.
The goal in part one of the experiment was to determine the pH of different household items and to then find any patterns that occurred in them. The objective in part two was to determine the concentration of acetic acid in vinegar. Part one was achieved by putting approximately 3 mL of a substance into a beaker, and then placing a pH probe into the beaker to record the pH of each solution. Part two was conducted in three separate trials.
A mixture of distilled vinegar and deionized vinegar was added to a beaker, and in intervals, small amounts of a NaOH base were added to the solution, and the pH was recorded with a pH probe each time. The amount of NaOH was recorded into LoggerPro, creating a table displaying the resulting pH and the first and second derivatives. The first derivative was used, which displayed the rate at which pH was changing the greatest with respect to the volume.
A titration curve was formed, which displayed the equivalence point to determine the concentration of acetic acid in vinegar. In part two, it was crucial to add the correct amounts of deionized water and NaOH to the vinegar, and also extremely important to take and record the correct measurements. The concentration was found to be 4.0% acetic acid in vinegar.