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Experiment 7 Plop, Plop, Fizz, FizzBackground |
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CHEMISTRY HOME
| You have a stomachache or heartburn. What do you do? Well, if you are like most of us you grab a bottle of antacid tablets or Maalox© and hope that they “cool the burn.” Have you ever wondered why or how the antacid works? Well, acid-base chemistry can explain both the how and why of antacid efficiency. In your stomach you have a large reservoir of hydrochloric acid (HCl) with a pH of about 2.0 that your body uses to digest food. In times of stress or when you overindulge, stomach acid can drop to a pH about 1.0 or even lower. Remember, the lower the pH, the higher the acid concentration. This condition is called hyperacidity and is what causes your stomach to be upset and your heart to “burn.” Antacids neutralize this strong acid by means of an acid-base reaction. Today in lab we are going to compare some over the counter antacids in order to determine which is the most efficient at neutralizing stomach acid. We will do this by reacting various antacids with an excess of 0.1M HCl. For example, if I place 30 mL of 0.1M HCl (0.03L x 0.1mol/L = 0.003 mol HCl) in a beaker and then add an antacid tablet, the antacid tablet will absorb some but not all of the acid. The acid that remains will then need to be neutralized by a base. To do this, you will titrate the remaining acid solution with 0.1M NaOH until the solution reaches a pH of ~7.0. A pH of 7.0 indicates that the solution has been neutralized. HCl(aq) + NaOH(aq) Since HCl and NaOH react in a one mole to one mole manner, by subtracting the amount of NaOH required to neutralize the solution from the amount of acid originally added, we can figure out how much of the acid the antacid tablets neutralized. So if in the example above, 0.0015 mol of the acid added was neutralized by the base, this must mean that 0.0015 mol of the acid was neutralized by the antacid tablet since 0.0030 mol– 0.0015 mols = 0.0015 mol. This process is called a “back titration” and it is necessary to do this for two reasons: 1) There are several ingredients in most antacids that prevent a direct titration from being accurate and 2) you always want to titrate base into acid for safety’s sake. |
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NaCl(aq) + H2O(l)