Question

A sample of oxygen gas is collected over water.
The volume of gas collected is 0.250 L at 26°C and
765 torr total pressure. (Water vapor pressure at 26°C = 25.22 torr)

How many grams of oxygen gas are collected?

Answer 1

The mass of the oxygen gas collected over water is 0.317 g

How to determine the mole of oxygen  

• Volume (V) = 0.250 L
• Temperature (T) = 26 ˚C = 26 + 273 = 299 K
• Pressure (P) = 765 – 25.22 = 739.78 torr = 739.78 / 760 = 0.973 atm
• Gas constant (R) = 0.0821 atm.L/Kmol

• Number of mole (n) =?

The number of mole can be obtained as by using the ideal gas equation as illustrated below:

n = PV / RT

n = (0.973 × 0.25) / (0.0821 × 299)

n = 0.0099 mole

How to determine the mass of oxygen collected

• Mole of oxygen = 0.0099 mole
• Molar mass of oxygen = 32 g/mol

• Mass of oxygen =?

Mass = mole × molar mass

Mass of oxygen = 0.0099 × 32

Mass of oxygen = 0.317 g

Learn more about ideal gas equation:

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