Here is one problem of mine:
Calculate the total number of atoms in 8.5g of CH2Cl2. Molar mass of CH2Cl2 is 85 g/mol
Avogadro constant 6.0*10^23
so you can calculate the number of moles coz you've got the mass (8.5g) and you've got the molar mass (85g/mol)
then just sub it into the equation and you're good
So you wanted to say that we need to multiply moles with avogadro constant which is equal to number of molecules divided by atoms.
mass = Mr x moles
equation first. you have the mass (8.5g) and you have the Mr/molar mass (85) so in order to find the number of moles, you'll have to divide the mass by the Mr.
then you multiply by Avogadro's constant to find the number of molecules or atoms.
First you gotta determine the number of moles you have of CH2Cl2: so (8.5g)/(85g/mol) = 0.1mol
Then multiply your answer by Avogadro's constant: 0.1 * 6.022*10^23 = 6.022*10^22 molecules in 8.5g of CH2Cl2
Hope that helps