Question #cfef7

2 Answers
Feb 1, 2015

At STP, 1 mole of any ideal gas occupies exactly "22.4 L" - this is known as the molar volume of a gas at STP. You were given "15.0 L", which automatically means that you have less than 1 mole.

"15.0 L" * ("1 mole")/("22.4 L") = "0.670 moles oxygen"

The link between moles and grams (and vice versa) is made through molar mass; a compound's (or an element's) molar mass expresses the weight in grams of 1 mole of that particular compound.

Since oxygen gas exists as a diatomic molecule - "O"_2, its molar mass will be twice that of one oxygen atom, which has a molar mass of "16.0 g/mol".

Therefore, the mass of oxygen in grams will be

"0.670 moles O"_2 * ("32.0 "g)/("1 mole O"_2) = "21.4 g"

Feb 2, 2015

The mass of oxygen gas is 21.43g

At STP 1 mole of gas has a volume of 22.4 L

Oxygen has the molecular formula O_2.

The A_r of oxygen = 16

So the M_r of O_2=(2xx16)=32

So 1 mole of O_2 weighs 32g

This means that 22.4 L weighs 32g

So 1L weighs (32)/(22.4)g

So 15 L weighs (32)/(22.4)xx15=21.43g