Question

A balloon contains 7.36 g of oxygen gas (O2). How many oxygen molecules are in the balloon?

Answer 1

Avagadros constant states that 1 mol of any substance is made of 6.022 x 10^23 units.
These units could be atoms making up elements or molecules making up compounds.
1 mol of molecular oxygen (O2) is made of 6.022 x 10^23 molecules of O2
The mass of 1 mol of O2 is 32 g/mol
This means that the number of oxygen molecules in 32 g are 6.022 x 10^23 molecules
Therefore in 7.36 g of oxygen gas there are - 6.022 x 10^23 /32 g/mol x 7.36 g = 1.39 x 10^23 oxygen molecules
Answer is 1.39 x 10^23 oxygen molecules