Quantitative Analysis ANALYSIS OF ANTACIDS Many people experience indigestion after eating. Indigestion can result from eating highly spiced foods, eating during high stress times (such as just before science tests), or simply eating too much food. When you eat food, your stomach secretes hydrochloric acid which aids in the digestion of food. If too much acid is secreted, acid indigestion results. This is a condition that we often call heartburn, due to the burning sensation in the esophagus. To relieve the discomfort and pain caused by the presence of excess stomach acid, many people take antacids. Antacids contain a base which neutralizes the stomach acid by chemically reacting with it to form a salt and water. There are many different bases used in the different commercial brands of antacids. In this experiment, we will determine the amount of base in the antacid Rolaids. Rolaids contains the base calcium carbonate (CaCO3). Some people complain that their antacid has a chalky taste, and it is no wonder; chalk is made of calcium carbonate as well. The hydrochloric acid in the stomach is neutralized by the calcium carbonate in Rolaids according to the following reaction: 2 HCl + CaCO3 Ö H2O + CO2 + CaCl2 The salt CaCl2 (calcium chloride) and water (H2O) are formed in this reaction. Also formed is the gas carbon dioxide (CO2) which may cause a bloated feeling in the stomach. The acid that is secreted in your stomach is approximately 0.1 M (moles per liter) hydrochloric acid. In this experiment, we will simulate the reaction that takes place in your stomach between the calcium carbonate in Rolaids and hydrochloric acid secreted by the stomach. When this reaction takes place, carbon dioxide gas is generated. When no more gas is being generated, it indicates that the calcium carbonate is completely neutralized. To determine when the acid is neutralized by the base, the indicator Congo Red will turn a pale blue color at the endpoint. 1. Neutralization with KNOWN Amount of Calcium Carbonate Materials: Mortal and pestle, two Rolaids tablets, 150 mL beaker, stirring rod, 10 mL syringe, hydrochloric acid, calcium carbonate powder, Congo Red indicator solution PROCEDURE Using a weighboat, mass approximately 0.5 g of calcium carbonate. Add this to the 150 mL beaker and dilute with 100 mL of distilled water. Add 5 drops of Congo Red indicator solution. Record the mass of the calcium carbonate added. Fill the 10 mL syringe with hydrochloric acid and add the acid to the calcium carbonate slowly while stirring continuously. Add large volumes (1.0 mL) of acid at first, and then continue by adding smaller volumes (0.5 mL) and finally add the HCl dropwise when the indicator begins to turn a pale blue color. Add the HCl solution until a pale blue solution remains for 30 seconds while stirring. This is the endpoint of the reaction where the acid has been neutralized by the calcium carbonate. Record the volume of HCl added and repeat the procedure for a second sample of calcium carbonate. Trial Mass of Calcium Volume of HCl Carbonate 1 0.50 g 10.0 mL 2 0.50 g 11.0 mL 2. Neutralization of Rolaids: An UNKNOWN Amount of Calcium Carbonate Mass one Rolaids tablet and record the mass of the tablet. Crush the tablet with a mortar and pestle and add the powder to a clean 150 mL beaker. Dilute with 100 mL of distilled water and add 5 drops of Congo Red indicator solution. With the 10 mL syringe add the HCl solution as you did with the calcium carbonate. Stir continuously while adding the acid. You may observe the solution change from a pale red to a pale purple color, and then change back to red again. This is because the reaction between the acid and base is relatively slow. The endpoint will be a pale blue solution which remains with continued strirring. Record the volumes of the HCl used for the tablet and repeat the procedure for a second tablet. Tablet Mass of Tablet Volume of HCl 1 1.25 g 11.5 mL 2 1.25 g 11.0 mL Calculate the amount of calcium carbonate in each antacid tablet. 0.50 g CaCO3 / 10.5 mL HCl = X g CaCO3 / 11.25 mL HCl 0.53 g CaCO3 Look at the bottle of antacid. How do your values compare with the manufacturer’s label? The manufacturer states that there is 500 mg (0.50 g) per tablet. The results are similar. What is the percent composition by mass of calcium carbonate in the tablet? 0.53 g / 1.25 g (x 100) = 42.4 % CaCO3 per tablet The extra-strength antacid tablet is advertised to have 50% more active ingredient. How many milligrams (according to your data) would an extra-strength tablet have? 0.53 g x 1.5 = 0.795 g .