# How many grams of O_2 are in 5.0 mol of the element?

Assume that:
n = number of moles (mol)
m = mass of substance (g)
M = molar mass (g/mol)

In ${O}_{2}$, the number of moles (n) has been provided for you = 5 moles.

In order to find the mass (m) of ${O}_{2}$, you first have to find the molar mass (M) of ${O}_{2}$.

Use this formula to help you: $n = m \div M$.

You know that ${O}_{2}$ is composed of 2 atoms of Oxygen.

If you look in your periodic table, the molar mass (is the atomic weight) of Oxygen is 16.0 g/mol.

Since there are 2 atoms in ${O}_{2}$, you have to multiply the number of atoms provided by the molar mass of each atom. Which is 2 $\times$ 16.0 g/mol therefore it will give you 32.0 g/mol as the molar mass (M).

Your final step is to find the mass (m) of ${O}_{2}$.

Refer back to this formula to help you: $n = m \div M$. Now you have to make $m$ as the subject (I'm not sure whether have you learned making an alphabet as a subject in Algebra).

To make $m$ as the subject, send $M$ to the left hand side therefore it will be multiplied by $n$. Now your formula should look like : $n \times M = m$.

Therefore, 5 moles $\times$ 32.0 g/mol = 160 grams is the mass (m) when there are 5 moles of ${O}_{2}$.

(I'm so sorry if my explanation is too long, but I'm trying my best so you could understand.)