NSC 101 Laboratory for 4/28/98

Effectiveness of Antacids

In this lab you will test several popular antacids for their ability to neutralize stomach acid (HCl). The ingredients are obtained from each antacid package. You will determine the reaction equation for each and then balanced it. Each antacid is tested and ranked by its effectiveness (Eff) given by

Eff = (ml of HCl) / (gms of antacid)

Equipment:

    100 ml or 50 ml burets, methyl orange indicator, 200 ml florence or erhlenmeyer flask, waste beakers, grinding bowl, various antacid tablets, .1 M HCl and .1M NaOH.

Procedure:

    First, note all the ingredients with their weight per tablet as given on the package of each antacid. Determine what reaction with HCl will take place and then balance the equation. This information will be used for later discussion.

    About half a tablet or less of each antacid is weighed and then dissolved in 50 ml of .1 M HCl (stomach acid). A few drops of methyl orange will turn the solution pink if it is acidic. If it is not pink, slowly add more HCl, carefully measured from the buret, until it stays red.

    Now slowly back titrate by adding .1 M NaOH, swirling constantly until it just turns orange-yellow. Subtract the ml of NaOH from the total ml of HCl to find the ml of HCl neutralized by the antacid. (This back titration is necessary because excess acid is required to make sure all of the active ingredients in the tablet react.) Tabulate the effectiveness E = (ml of HCl)/(gm of antacid) for each antacid and determine their ranking in terms of effectiveness. Then examine the balanced equations for each and consider the molecule ratio of neutralization. Find the molecular weight of each ingredient and then reconsider the question.