Chan asked in 科學及數學化學 · 9 years ago

# Ideal Gas Law Calculation

Oxygen gas generated by the decomposition of potassium chlorate is collected over water. The volume of gases collected at 297K and 101.6kPa is 0.128dm3. Calculate the mass of oxygen gas obtained. The pressure of the water vapour at 297K is 2.99kPa.

I also want to ask do I need to consider to water vapour in this case? Explain.

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• 土扁
Lv 7
9 years ago

Youmust consider the pressure of the water vapour in this question. As oxygen is collected over water, thepressure of the gas product (101.6 kPa) is the sum of the (partial) pressure ofoxygen and that of the water vapour. Therefore,the pressure of oxygen in equal to the difference between the total pressureand the pressure of the water vapour.

The steps of calculation are shown below :

Temperature, T = 297 K

Pressure, P = (101.6 - 2.99) ´ 10³ Pa = 98610 Pa

Volume, V = 0.128 ´ 10⁻³ m³

Gas constant, R = 8.314 J mol⁻¹ K⁻¹

Molar mass of oxygen, O2 = 16 ´ 2 = 32 g mol⁻¹

PV = nRT

PV = (m/M)RT

m = PVM / RT

The mass of oxygen, m

= 98610 ´(0.128 ´ 10⁻³) ´ 32 / (8.314 ´ 297)

= 0.164 g

Source(s): 土扁