Question

P4O10(s) + 6 H2SO4(l)  4 H3PO4(aq) + 6 SO3(g)

Pure H2SO4(l) has a density of 1.84 g/mL. If 45.0 mL of H2SO4(l) reacts:

What mass of P4O10 reacts?

45.0 mL X 1.84 g/mL X (1 mol/98.1 g) = 0.844 mol H2SO4

Moles P4O10 = 0.844 mol H2SO4 X (1 mol P4O10 / 6 mol H2SO4) = 0.141 mol P4O10
Mass P4O10 = 0.141 mol P4O10 X 283.9 g/mol = 39.9 g P4O10

What volume of SO3(g) at STP is produced? (2 marks)

0.844 mol H2SO4 X (6 mol SO3 / 6 mol H2SO4) = 0.844 mol SO3

At STP, 1 mol of any gas has a volume of 22.4 L. So,
Volume SO3 = 0.844 mol X (22.4 L/mol) = 18.9 L SO3