This worked example problem shows how to convert the number grams of a molecule to the number of moles of the molecule. Why would you need to do this? Mainly this type of conversion problem arises when you are given (or measure) the mass of a sample in grams and then need to work a ratio or balanced equation problem that requires moles.

Problem

Determine the number of moles of CO₂ in 454 grams of CO₂.

Solution

First, look up the atomic masses for carbon and oxygen from the Periodic Table. The atomic mass of C is 12.01 and the atomic mass of O is 16.00. The formula mass of CO₂ is:

12.01 + 2(16.00) = 44.01

Thus, one mole of CO₂ weighs 44.01 grams. This relation provides a conversion factor to go from grams to moles. Using the factor 1 mol/44.01 g:

moles CO₂ = 454 g x 1 mol/44.01 g = 10.3 moles

Answer

There are 10.3 moles CO₂ in 454 grams of CO₂

How To Convert Moles To Grams