Potassium Perchlorate, KCIO_4, decomposes on heating to form potassium chloride

Question

Potassium Perchlorate, KCIO_4, decomposes on heating to form potassium chloride elemental oxygen. a. Write a balanced molecular equation for the thermal decomposition of potassium perchlorate. Using a setup like this experiment, the following data were collected: mass of sample before heating 2.6865 g mass of residue after heating 2.0475 g volume of water displaced 516 mL atmospheric pressure 750.7 torr water temperature 27.0degreeC What is the percent mass KCIO_4 the sample being heated? What volume would this sample of oxygen occupy collected at standard if temperature and pressure? What is the molar volume at STP of O_2, according to these data?

Explanation / Answer

Q3.

a)

KClO4(s) --> KClO(s) + O2(g)

balance

KClO4(s) --> KCl(s) + 2O2(g)

b)

% mass of KClO4 in sample

mass sample = 2.6865 g

mass after heat = 2.0475

Vdisplace = 516 mL

Patm = 750.7 torr

P°vap = 27°C = 26.6642 torr

Pgas = 750.7-26.6642 = 724.035 torr

mol of gas

PV = nRT

n = PV/(RT) = 724.035*0.516 / (62.4 * 300) = 0.0199573 mol

mol of O2 = 0.0199573

then.. ratio was 2 mol of O2 --> 1 mol of KClO4

so

0.0199573 mol of O2 --> 0.0199573/2 = 0.00997865 mol of KClO4

mass of KClO4 = mol*MW = 138.55 *0.00997865 = 1.38254 g of KClO4

% mass = 1.38254/2.6865*100% = 0.51462*100 = 51.6%

c)

V of sample is Oxygen -->

1 mol of O2 at STP = 22.4L

0.0199573 mol = 0.0199573*22.4 = 0.447043 Liters of O2 = 447 mL of O2

d)

Molar volume = Volume/ mol = 516/0.0199573 = 25855.2008 mL/mol

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