One way to reduce air pollution is to remove potential pollutant gases from an exhaust stream before they are released into the air. Carbon dioxide can be removed from a stream of gas by reacting it with calcium oxide to form calcium carbonate. If we react 5.50 L of CO₂ at STP with excess CaO, what mass of calcium carbonate will form?

Strategy You should recognize this as a reaction stoichiometry problem because it is asking us how much CaCO₃ will be produced. As for any stoichiometry problem, we should write a balanced chemical equation for the reaction. Then we convert the volume of gas into moles and proceed as usual. Because the gas volume given is at STP, we can use the molar volume we calculated above as a conversion factor.