What does the atomic mass bave to do with the mass in grams ?

1 mol of an atom = the atomic mass of an atom in grams
ie.. 1 mol O2= 32.00 g

the formula for doing this is Avogadro's number (6.02x10^23)
So it would be set up as a dimensional analysis problem. You need to convert the amount of molecules to moles, then grams. so
molecules of compound/1    6.02 x 10^23 molecules/1 mol   1 mol (compound)/ (x) grams

so if the compound is H2SO4 you add up H=2.02   S= 32.06 O=64.00  1mol H2SO4= 98.08 g

the atomic mass assigned to each element is the mass in grams of one mole of that element. to get the mass of a single atom, you could take the atomic mass and divide it by avogadro's number to get the approximate mass of a single atom of a given element. However, the atomic mass assigned to each element is actually an average of all it's isotopes. For example, one mole of carbon-12 weighs exactly 12 g, but because carbon-12 isn't the only isotope of carbon, you must also include the weight of other isotopes. hence, the molar mass of carbon is 12.011 which is the atomic mass that is assigned to it on the periodic table.

in order to get an accurate mass value for a single atom, you're better off adding up the masses of its constituents; i.e, electrons, protons, neutrons