Which has a greater number of atoms: 3.0 g of iron, Fe, or 2.0 g of sulfur, S?

1 Answer
Nov 11, 2015

#"2.0 g"# of sulfur


In order to be able to determine how many atoms you have in those two samples, you first need to find how many moles of each element you have here.

As you know, one mole of any element contains exactly #6.022 * 10^(23)# atoms of that element - this is known as Avogadro's number.

Moreover, en element's molar mass will tell you what the mass of one mole of said element is. The idea is that the difference between the mass of one mole of iron and one mole of sulfur is determined by the difference between the actual atoms of the two elements.

The heavier an individual atom is, the heavier one mole of such atoms will be.

So, use iron and sulfur's respective molar mass to determine how many moles of each you have

#"For Fe: " 3.0color(red)(cancel(color(black)("g"))) * "1 mole Fe"/(55.845color(red)(cancel(color(black)("g")))) = "0.0537 moles Fe"#

#"For S: " 2.0color(red)(cancel(color(black)("g"))) * "1 mole S"/(32.065color(red)(cancel(color(black)("g")))) = "0.0624 moles S"#

Since you have more moles of sulfur, you will also have more atoms of sulfur.

More specifically, the two samples will contain

#0.0537color(red)(cancel(color(black)("moles"))) * (6.022 * 10^(23)"atoms of Fe")/(1color(red)(cancel(color(black)("mole")))) = 3.23 * 10^(22)"atoms of Fe"#


#0.0624color(red)(cancel(color(black)("moles"))) * (6.022 * 10^(23)"atoms of S")/(1color(red)(cancel(color(black)("mole")))) = 3.76 * 10^(22)"atoms of S"#