The method used by Joseph Priestly (credited with the discovery of oxygen) to pr

Question

The method used by Joseph Priestly (credited with the discovery of oxygen) to produce oxygen made use of the thermal decomposition of mercury(II) oxide: HgO(s) Hg(l) + O2 (g) (unbalanced) Calculate the volume of oxygen gas, measured at 30.0°C and 725 torr that can be produced from complete decomposition of 2.06 grams of mercury(II) oxide.

_____ L

2.

Consider the following reaction for the combustion of octane, C8H18:

2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(l)

What volume of oxygen gas at STP would be needed for the complete combustion of 10.4 g of octane?

_________ L O2

Explanation / Answer

1.

1 mol of HgO --> 1 mol of O2

mol of HgO = mass/MW = 2.06/216.5894 = 0.009511 mol

PV = nRT

V = nRT/P = 0.009511*0.082*(30+273)/(725/760) = 0.247718 L

2.

10.4 g of octane

mol = m/MW = 10.4/114 = 0.09122 mol of octane

ratio is 2:25

25/2*0.09122 = 1.14025 mol of O2

1 mol = 22.4 L at STP

1.14025 mol = 1.14025*22.4 = 25.5416 L of O2

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