In this lesson you will learn:

What Avogadro’s Number is and What Molar Volume is

Amedeo Avogadro was an Italian Scientist. He gave his name to the number of particles

in a mole (see our video on ‘What is a Mole’). Avogadro’s Number, NA, or the Avogadro Constant

is 6.02 X 1023 Mol-1. It is the number of atoms per mole of the carbon-12 isotope.

For atoms, the mass of Avogadro’s number of particles is equal to their relative atomic

mass in grams. So, the mass of Avogadro’s number of hydrogen

atoms is 1.0g and the mass of Avogadro’s number of chlorine

atoms is 35.5g and For molecules, the mass of Avogadro’s number

of particles is equal to their relative molecular mass in grams.

So, the mass of Avogadro’s number of hydrogen molecules (H2) is 2.0g and

the mass of Avogadro’s number of chlorine molecules (Cl2) is 71.0g

If someone asks you ‘What is the mass of Avogadro’s number of chlorine particles?’ you cannot

answer. If by chlorine particles they mean chlorine

atoms, the answer is 35.5g. If, however, by chlorine particles they mean

chlorine molecules, the answer is 71.0g What is Molar Volume?

In 1811, Avogadro proposed his hypothesis which stated ‘Equal volumes of gases at the

same temperature and pressure contain the same number of molecules’. This hypothesis

made it much easier to perform calculations involving gases. So one mole (Avogadro’s number

of molecules) of any gas will occupy the same volume, at the same temperature and pressure,

as one mole of any other gas. The volume occupied by one mole of a gas is called the Molar Volume.

Molar volume is measured in dm3mol-1 At room temperature and pressure (RTP) the

molar volume is taken as 24.0 dm3mol-1 Let us look at a calculation.

What is the volume at RTP occupied by 4g oxygen? Pause the video while you work it out. Then

start the video to check your answer. What do we know?

We know that one mole of any gas at RTP occupies 24dm3

One mole of oxygen gas (O2) has a mass of 32g

So 32g of oxygen gas at RTP occupies a volume of 24dm3

Therefore 1g of oxygen gas at RTP occupies a volume of (24/32) dm3

and so 4g of oxygen gas at RTP occupies a volume of 4 X (24/32) dm3=3 dm3

So, to recap: Avogadro’s number (or constant), NA, is 6.02

X 1023 Mol-1 Molar Volume is the volume occupied by one

mole of gas and is 24.0 dm3mol-1 at RTP Equal volumes of gases at the same temperature

and pressure contain the same number of molecules — this is known as Avogadro’s Hypothesis

cjc pls

great video thank you

Science is fun

Actually

No

34k views and only 4 comments wow

Thanks mate

One mole of any gas occupies exactly 22.4 l per mole isn't it 22.7?

this is outdated; stp (0 degrees Celsius and 101.325 kPa) is 22.4L per mol while satp (25 degrees Celsius and 100 kPa) is 24.8L per mol.

Thanks a lot