To find the percent composition of each element, the following calculations are carried out.The same percentages would be obtained if we used the empirical formula for this calculation.3 . D
According to the balanced equation, one mole of CaC 2 yields one mole of C 2 H 2 . Therefore, if
0.400 moles of CaC 2 were used, 0.400 moles of C 2 H 2 would be produced. The molecular weight
of C 2 H 2 is 2(12 g/mol) + 2(1 g/mol) = 26 g/mol. Thus, the mass of C 2 H 2 is 26 g/mol × 0.400 mol =
10.4 g.
4 . A
Since the only change is that the Na from CH 3 CO 2 Na exchanges with the H from HClO 4 , this is a
double displacement reaction. Alternatively, this reaction could be classified as a
neutralization, since it is an acid and a base that react.
5 . A
According to the balanced equation, one mole of salicylic acid will yield one mole of aspirin.
Therefore, to solve this question, the number of moles of aspirin in six 5-grain tablets, or 30
grains of aspirin, must be determined, using the following relationship.
Therefore, the weight of the aspirin produced is about 2 grams, which must be converted to
moles. The molecular weight of aspirin is 9(C) + 8(H) + 4(O) = 9(12 g/mol) + 8(1 g/mol) + 4(16
g/mol) = 180 g/mol. Then, the number of moles in 2g of aspirin is calculated.