How many moles of carbon dioxide molecules are there in 138 g of carbon dioxide (CO₂) ?
To find the number of moles of molecules that we have in the sample we need the molar mass of CO₂. To calculate the molar mass of our compound we have to look for the atomic mass of its elements. They are:
C: 12.01 amu
O: 16.00 amu
With these values we can calculate the molar mass of CO₂. Since one molecule of CO₂ has 2 atoms of O and 1 atom of C, the molar mass of CO₂ is:
molar mass of CO₂ = 12.01 + 2 * 16.00
molar mass of CO₂ = 44.01 g/mol
Now that we know that the mass of 1 mol of CO₂ is 44.01 g, let's find the number of moles of CO₂ that we have in 138 g of it.
number of moles = mass of the sample of CO₂/molar mass of CO₂
number of moles = 138 g/(44.01 g/mol)
number of moles = 3.14 moles
Answer: there are 3.14 moles of carbon dioxide molecules in 138 g of it.