Small quantities of oxygen gas are sometimes generated by heating KClO3 in the presence of MnO2 as a catalyst?

Question

2KClO3(s) → 2KCl(s) + 3O2(g)

what volume (mL) of O2 is collected over water at 24.0 C by the reaction of 0.251g of KClO3 if the barometric pressure is 721.8 mm Hg.

The vapor pressure of water at 24.0 C is 22.4 mm Hg

Answer 1

The MW of KClO3 is 122.55 (ref.), so 0.251 g KClO3 is .0020481 M. This will evolve 3/2 * .0020481 = .0030722 M O2 * 22.4 L/M = .068818 L O2 at STP. Correcting for temperature, pressure and partial pressure H2O, multiply by 297/273 * 760 / (721.8 - 22.4) and volume at given temp. and press. = 0.081354 L.