Determine the number of moles in 4.75 X 1020 atoms of Lead

Explanation:

To convert from moles to atoms, we must use Avogadro's Number. Avogadro's Number

1. Set up ratio

We can use Avogadro's Number as a fraction or ratio.

2. Convert atoms to moles

Multiply the given number of atoms by the ratio.

Flip the fraction so that the atoms of lead can cancel each other out.

3. Round

The original measurement of 4.75 had 3 significant figures (4, 7, and 5).

We must round our answer to 3 sig figs, which is the hundredth place for the number found.

The 7 in the thousandth place tells us to round the 8 up to a 9 in the hundredth place.

There are 7.89*10⁻⁴ moles of lead in 4.75*10²⁰ atoms of lead.