assume you know the number of moles of oxygen (for example, 5).Here is the question: how much under normal circumstances take these 5 moles?The solution will be: under normal conditions, the volume of 1 mole of any gas is constant and is approximately equal to 22.4 liters.Consequently, five moles of oxygen under normal conditions will occupy volume 22.4 * 5 = 112 liters.
Well, if you know the mass of oxygen?Assume 96 grams.How much they will take under normal conditions?First, find out how many moles of oxyg
en contained in 96 grams of the substance.The molar mass of oxygen (based on the formula O2) = 32 grams / mole.Consequently, 96 grams - is 3 mol.Making multiplication, the following answers: 22.4 * 3 = 67.2 liters.
And if you need to determine the amount of oxygen under conditions different from normal?Then you come to the aid of the universal equation of Clapeyron-Mendeleev, describing the state of the so-called "ideal gas".It is written in this form:

PV = RTM / m, where P - the gas pressure in Pascals, V - its volume in liters, R - universal gas constant, T - gas temperature in degrees Kelvin, M - mass of the gas, m -its molar mass.
Transforming the equation, we get:

V = RTM / mP.
As you can see, if you have the necessary data for the calculations (temperature, weight and pressure of oxygen), calculate its volume is very simple.Since the values ​​of R (8,31) and m (32), and so you know.