Let's see that in the periodic table, we have the molar mass of every element. In this case, carbon has a molar mass of 12 g/mol and oxygen of 16 g/mol. The conversion from grams to moles is dividing the mass by the sum of the molar mass of the compound.
In this case, we have 1 atom of carbon and two atoms of oxygen. Doing the algebraic sum for each of them with their molar mass we're going to obtain:
[tex]\text{Molar mass of CO}_2=1\cdot12\frac{g}{mol}+2\cdot16\frac{g\text{ }}{mol}=44\frac{g\text{ }}{mol}[/tex]So, 225 g of carbon dioxide will be:
[tex]225gCO_2\cdot\frac{1molCO_2}{44gCO_2}=5.11molCO_2.[/tex]So, finally, we have 5.11 moles in 225 grams of CO2.
