Download Quantitative Analysis

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
Volume of HCl
1
Mass of Calcium
Carbonate
0.50 g
2
0.50 g
11.0 mL
10.0 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
1
Mass of Tablet
1.25 g
Volume of HCl
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