Antacid Analysis and the Determination of the Percent of acetic acid in Vinegar
Introduction:
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).
Data:
[img:210695bd20]http://www.collegepimp.com/echeat/lab15.gif[/img:210695bd20]
Discussion:
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.
The Essay on Acid- Base Titration Lab
1. When the end point is reached in an acid-base titration, the relationship between the concentrations of OH- and H3O+ are that they are equal. This doesn’t mean that the pH will be neutral, but the concentrations of both will be the same in a titration. 2. The pH of the end point is determined by what kind of indicator is used to indicate when the end point I reached. In this experiment, ...
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 moles of HCl. Knowing that 70mL of .3M HCl is 21 millimoles, subtracting from this the excess millimoles HCl, we found 8 millimoles HCl reacted with CaCO3 in Tums, and 14 millimoles reacted with CaCO3 in Rolaids. This means that the antacid in Tums weighs about .801g while Rolaids contains 1.40g of antacid. Tums was 60.6% antacid, while Rolaids was 95.2%. Theoretically, all of this means that Rolaids is better since more acid will be consumed by it.
If the concentration of HCl was not correct, then the millimoles of HCl would be off, which would adversely affect the amount of HCl calculated to react with the antacid. However, both antacids would be off by the same amount, so if the point was to determine which one reacts with more acid, this would be mostly a non-issue. If the antacid was not fully dissolved then not all of the HCl would react with it, making it appear that it consumes less acid than it can.
