Calculate the mass of 500 atoms of iron (fe)?

##4.63*10^-20## gram

You can get to the answer in two steps:

1. calculate: 500 atoms = ##color(red)x## mol ? using Avogadro's constant.
2. calculate: ##color(red)x## mol = ##color(red)?## grams, using the atomic mass of Iron.

Step 1 Avogadro's constant says that ##1## mole of any atom contains ##6.022*10^23## atoms. In this case you have ##500## atoms:

##(500 color(red)cancel(color(black)("atoms")))/ (6.022*10^23 color(red)cancel(color(black)("atoms"))/"mol"## = ##8.30*10^-22 mol##

Step 2 The atomic mass of iron (Fe) will give you the weight of one mole of this molecule: ##1## mol = ##55.845## gram:

##55.845 g/(color(red)cancel color(black)"mol") * 8.30*10^-22 color(red)cancel color(black)"mol"## = ##4.63*10^-20 g##

So the 500 iron atoms weigh ##color(red)(4.63*10^-20) color(red)"grams"##.