The atomic mass of silver is 108 u and molar mass of silver is 108 g/mol. This means there are 6.023×1023 atoms of silver in 108 of silver. Thus
6.023×1023 atoms of silver =108g
1 atom of silver = 108(6.023×23)g
Thus the mass of an atom of silver is 1.7931×10−22g.
The atomic mass of carbon is 12 u while that of oxygen is 16 u. The chemical formula of carbon dioxide is CO2, so the molecular mass of carbon dioxide is 12+2×(16)=44u. The molar mass of carbon dioxide is 44g. This means there are 6.023×1023 moleucles of CO2 in 44 g of CO2. Thus
6.023×1023 moleucles of CO2=44g of CO2
1 molecule of CO2=44(6.023×1023)g
So the mass of a moleucle of CO2=7.305×10−22g
A mole is a convenient counting unit whenever one is dealing with numbers of atoms or molecules. It is equal to Avogadro's number (NA), namely 6.022×1023. If we have one mole of water, then we know that it will have a mass of 2 grams (for 2 moles of H atoms) +16 grams (for one mole O atom) =18 grams.