Calcium carbonate reacts with hydrochloric acid and produces carbon dioxide, as
ID: 594026 • Letter: C
Question
Calcium carbonate reacts with hydrochloric acid and produces carbon dioxide, as shown in the following equation:
CaCO3(s)+2HCl(aq)Ca2+(aq)+2Cl(aq)+H2O(l)+CO2(g)(1)(1)CaCO3(s)+2HCl(aq)Ca2+(aq)+2Cl(aq)+H2O(l)+CO2(g)
which can be simplified as:
CO23(aq)+2H+(aq)H2O(l)+CO2(g)(2)(2)CO32(aq)+2H+(aq)H2O(l)+CO2(g)
By reacting the antacid with excess acid and then collecting the carbon dioxide produced in a constant predetermined volume, we will be able to use the ideal gas law and the molecular weight of calcium carbonate (100.0869 g/mol) to determine the weight percent of calcium carbonate in the antacid tablet.
PV=nRT(Ideal Gas Law)
The pressure of the flask will be monitored with a pressure sensor and temperature will be monitored using a temperature probe, both connected to a Verniercomputer interface unit. Using the ideal gas law and a known standard sample of calcium carbonate you will determine the volume of the flask
Why do we use standard calcium carbonate to determine the volume of the flask? Why can’t we use the stated volume of the flask (125mL) in our calculations?
Explanation / Answer
A standard sample of calcium carbonate (CaCO3) is used because the percent purity is known with certainty. This simply means that the standard sample has fewer impurities and the sample contains mostly pure CaCO3. CaCO3 decomposes to produce carbon dioxide, CO2 in a 1:1 molar ratio. Hence, knowing the percent purity of the standard sample, it is easy to ascertain the exact mass and hence, the number of mole(s) of CaCO3 that has gone into the reaction. Consequently, we can easily determine the number of mole(s) of CO2 generated.
The volume of the flask is not used, since the reaction uses aqueous acid and some water vapor may be trapped in the flask. This trapped vapor will occupy a portion of the flask and the actual volume of CO2 produced will be slightly off from the volume of the flask. Another possibility may be that CO2 escapes during the reaction and hence, we cannot use the volume of the flask to determine the volume of CO2 generated.