Lab - Antacid and Acetic Acid in Vinegar
Uploaded by erobinson on Apr 30, 2004
Antacid Analysis and the Determination of the Percent of Acetic Acid in Vinegar
The purpose of this lab is to teach us three new methods and give us a better understanding of acid-base reactions. We will be learning how to standardize a solution, determine % acid in a solution (Vinegar), and how to determine neutralization capacity (antacids).
The first part of this lab was a required step for the next two parts. We standardized NaOH so that we could determine its exact Molarity. We used phenolphthalein as the indicator for neutralization. We titrated KHP with the NaOH until we reached the equivalence point which told us the moles of H+ ions equaled that of OH- ions. By knowing moles of KHP, we knew moles of NaOH titrated. Dividing moles NaOH over liters titrated we found the average Molarity for three trials to be .290M. This is very close to the goal of .3M, and now we have a standardized solution of NaOH for the next parts of the lab.
Part two was to determine the moles of acetic acid and its percent in vinegar. Once again we used phenolphthalein as the indicator. We titrated 20mL of Vinegar with 34.6mL and 34.3mL of NaOH for trials 1 and 2 respectively, until the equivalence point was reached. Multiplying by the concentration found earlier of NaOH, we found .00986 and .00995 moles for each trial. Since only one H+ ion from acetic acid (Only one is bonded to the electronegative oxygen, giving up its electron) bonds with OH- we know that the moles of acid are the same as NaOH. Dividing by .020L of Vinegar gives us the concentration of .493M and .498M. We found an average of 2.85% acetic acid in Vinegar.
Part three was the most involved piece of the lab. The goal was to find the moles, mass, and % composition of the active ingredient in the antacids, Tums and Rolaids. We weighed each antacid to find total grams so we could find % composition later. We dissolved the antacids in excess HCl because they are insoluble in water. We added Thymol blue indicator for this solution. We then titrated the solution with NaOH until the equivalence point was reached. Rolaids required considerably less NaOH to reach this point. Since NaOH only reacts with the excess HCl not consumed by the base in the antacid, the number of moles of NaOH equals the excess...