CHEMISTRY · Single correct · A Level · Chemistry · Amount of substance · Amount of substance
Problem
In a lab procedure, solid Na2CO3 is added to an aqueous solution of HCl, and the CO2(g) that forms is collected in a gas syringe. The student then uses the measured temperature and pressure of the gas to calculate the number of moles of CO2 and, from that value, the number of moles of Na2CO3 consumed. Which of the following best explains why the balanced chemical equation is essential for the second part of this calculation?
(a) It lists the physical states of all species, so the student can identify which substance is in the gas phase and therefore measured in the syringe.
(b) It shows which reactant is limiting, so the measured moles of CO₂ can be converted directly to the amount of Na2CO3 consumed.
(c) It provides the mole ratio that links moles of CO₂ to moles of Na2CO3, ensuring conservation of atoms across the reaction.
(d) It contains the molar masses of the substances, making it possible to relate the moles of CO₂ to grams of Na2CO3.