Question 5.7: One way to reduce air pollution is to remove potential pollu......
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 CO_2 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 CaCO_3 will be produced. As for any stoichiometry problem, we should write a balanced chemical equation for the reaction. Then 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.
CO_2(g) + CaO(s) → CaCO_3(s)
5.50\;\mathrm{L\ CO}_{2}\times{\frac{1\;\mathrm{mol~CO}_{2}}{22.41\;\mathrm{L}\;\mathrm{CO}_{2}}}\times{\frac{1\;\mathrm{mol~CaCO}_{3}}{1\;\mathrm{mol~CO}_{2}}}\times{\frac{100.1\;\mathrm{g\;CaCO}_{3}}{1\;\mathrm{mol~CaCO}_{3}}}=24.6\;\mathrm{CaCO}_{3}
Analyze Your Answer From the molar volume at STP, we can see that 5.5 L would be about one-quarter of a mole of CO_2. So we should be making about onequarter mole of CaCO_3, and our answer agrees with that.
Discussion Note that the conversion factor of 22.4 L = 1 mole is valid only when the gas in question is at STP. You should be very careful not to use that molar volume for any other conditions! We could also have worked this problem by using the ideal gas law to find the volume of the CO_2, using the appropriate temperature and pressure for STP conditions.
In this example, a gas is converted to a solid product rather than being emitted into the air. What implications might this have for engineering design? Can you think of situations in which this type of pollution control scheme might cause problems?
Check Your Understanding SO_2 can be generated in the laboratory by heating ZnS with O_2. (The other product is zinc oxide.) If 14.5 L of oxygen at STP is reacted with excess zinc sulfide, what volume of SO_2 at STP is generated?