# What is the mass of oxygen in 8 moles of carbon dioxide?

Since carbon has an atomic mass of 12 and oxygen 16, the molecular mass of $C {O}_{2}$ is 44.
This means that the mass of 1 mole of $C {O}_{2}$ is $44 g$, of which $2 \times 16 = 32 g$ is $O$
So $8 m o l C {O}_{2} \leftrightarrow 8 \times 32 = 256 g O$