Hydrochloric acid (HCl) is one of the substances found in gastric juices secreted by the lining of the stomach. HCl is needed by the enzyme pepsin to catalyze the digestion of proteins in the food we eat. Heartburn is a symptom that results when the stomach produces too much acid (hyperacidity).
Antacids are bases used to neutralize the acid that causes heartburn. Despite the many commercial brand, almost all antacids act on excess stomach acid by neutralizing it with weak bases. The most common of these bases are hydroxides, carbonates, or bicarbonates. The following table contains a list of the active ingredients found in several common commercial antacids, and the reactions by which these antacids neutralize the HCl in stomach acid.
|Compound||Chemical Formula||Chemical Reaction|
|Aluminum hydroxide||Al(OH)3||Al(OH)3(s) + 3 HCl(aq) -----> AlCl3(aq) + 3 H2O(l)|
|Calcium carbonate||CaCO3||CaCO3(s) + 2 HCl(aq) -----> CaCl2(aq) + H2O(l) + CO2(g)|
|Magnesium carbonate||MgCO3||MgCO3(s) + 2 HCl(aq) -----> MgCl2(aq) + H2O(l) + CO2(g)|
|Magnesium hydroxide||Mg(OH)2||Mg(OH)2(s) + 2 HCl(aq) -----> MgCl2(aq) + 2 H2O(l)|
|Sodium bicarbonate||NaHCO3||NaHCO3(aq) + HCl(aq) -----> NaCl(aq) + H2O(l) + CO2(g)|
HClinitial – HCltitrated = HClneutralized
Put on your CHEMICAL SPLASH-PROOF SAFETY GOGGLES!
1. Clean, rinse, and fill a buret with NaOH solution just as you did in last week's experiment. Record the molarity of the NaOH and the initial NaOH volume reading from the buret (+0.02 mL).
2. Weigh an antacid table in a weighing boat and record the mass (+0.01 g). Transfer the tablet to a clean mortar and crush the tablet into a fine powder using the pestle.
3. Weigh about 0.2 grams (+0.01 g) of the ground up tablet powder and transfer it to a clean 250 mL Erlenmeyer flask.
4. Transfer about 20 mL (+0.02 mL) of the HCl to the flask from the acid buret located on the reagent bench. Record the molarity of the HCl and the initial and final volume readings from the buret (+0.02 mL).
5. Swirl the flask to help dissolve the antacid. Since the antacid tablet may contain inert ingredients, much of the tablet may not dissolve and the liquid will be cloudy. The active antacid ingredient will dissolve and react with the acid very quickly while the liquid will remain cloudy.
6. Add 3 - 4 drops of phenolphthalein indicator to the flask, and titrate the acid solution to a phenolphthalein endpoint. Record the final NaOH volume (+0.02 mL). Since the liquid is cloudy, the color change at the endpoint may be particularly hard to detect.
7. Repeat this analysis on two other brands of antacid tablets.
8. Before returning the buret to the lab bench, please rinse it out with a couple of water rinses.
Chemistry 104: Analysis of Commercial Antacid Tablets
Show all calculations on an attached second sheet.
Molarity of NaOH _______M
Molarity of HCl _______M
|Tablet 1||Tablet 2||Tablet 3|
|Antacid brand name||____________________||____________________||____________________|
|antacid tablet wt.||______________g||______________g||______________g|
|crushed antacid sample wt.||______________g||______________g||______________g|
|initial HCl buret reading||
|final HCl buret reading||______________mL||______________mL||______________mL|
|mL HCl delivered||______________mL||______________mL||______________mL|
|moles of HCl||______________moles||______________moles||______________moles|
|initial NaOH buret reading||______________mL||______________mL||______________mL|
|final NaOH buret reading||______________mL||______________mL||______________mL|
|mL NaOH delivered||______________mL||______________mL||______________mL|
|moles of NaOH||______________moles||______________moles||______________moles|
|moles of HCl neutralized
by antacid sample
|moles of HCl neutralized per antacid tablet||___________moles/tablet||___________moles/tablet||___________moles/tablet|
|cost per tablet||_____________$/tablet||_____________$/tablet||_____________$/tablet|
|cost per mol of HCl neutralized||________________$/mol||________________$/mol||________________$/mol|