Question

Which of the following has the greatest mass, in grams?

0.3 mol iron (Fe) atoms

1 atom of silver (Ag)

25 atoms of lead (Pb)

1 mole of hydrogen atoms (H)

Answer 1

Convert the number of atoms (or moles) to mass to compare these.

The atomic weight is the mass in grams of a mole of atoms. If the number is in moles, multiply the number by the atomic weight to get the mass.

If the number is in atoms (e.g. 1 silver atom), multiply the number of atoms by the mass of an individual atom. The mass of an individual atom is the atomic weight divided by the Avogadro's number, approx. 6x10^23.

Because the avogadro's number is many orders of magnitude larger than the ratios between the atomic weights, the 0.3 mol of iron atoms will have the greatest mass among these. (hehe... mass).