Which has more atoms, 2.00 grams of Lead or 2.00 grams of Iron? Please use Avogadro's number to help answer the question. Please explain why the answer you have is correct.

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ncchemist eNotes educator| Certified Educator

We have 2 grams of lead and 2 grams of iron.  We need to figure out which contains more atoms.  The number of atoms in a particular sample is easiest to find by working with moles.  One mole of any substance, by definition, is equal to Avogadro's number, or 6.022 x 10^23 atoms of that substance.  So first we should use the atomic weights of both elements to convert them from grams to moles.  We can then multiply the number of moles by Avogadro's number to find the number of atoms in each sample.

2 grams lead * (1 mole/207.2 g) = 0.0097 moles lead

0.0097 moles lead * (6.022 x 10^23 atoms/1 mole) = 5.81 x 10^21 atoms lead

2 grams iron * (1 mole/55.85 grams) = 0.036 moles iron

0.036 moles iron * (6.022 x 10^23 atoms/1 mole) = 2.16 x 10^22 atoms iron

As you can see, 2 grams of iron has more atoms than 2 grams of lead.  This makes intuitive sense since iron is the lighter of the two metals and therefore will have more atoms in 2 grams to equal the same weight of the heavier element lead.