Answer:
[tex]\boxed {\boxed {\sf 7.89*10^{-4} \ mol \ Pb}}[/tex]
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.
[tex]\frac{6.022*10^{23} \ atoms \ Pb}{1 \ mol \ Pb}[/tex]
2. Convert atoms to moles
Multiply the given number of atoms by the ratio.
[tex]4.75 *10^{20} \ atoms \ Pb *\frac{6.022*10^{23} \ atoms \ Pb}{1 \ mol \ Pb}[/tex]
Flip the fraction so that the atoms of lead can cancel each other out.
[tex]4.75 *10^{20} \ atoms \ Pb *\frac{1 \ mol \ Pb}{6.022*10^{23} \ atoms \ Pb}[/tex]
[tex]4.75 *10^{20} *\frac{1 \ mol \ Pb}{6.022*10^{23} }[/tex]
[tex]\frac{4.75 *10^{20} \ mol \ Pb}{6.022*10^{23} }[/tex]
[tex]7.88774494*10^{-4} \ mol \ Pb[/tex]
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.
[tex]7.88774494*10^{-4} \ mol \ Pb[/tex]
The 7 in the thousandth place tells us to round the 8 up to a 9 in the hundredth place.
[tex]7.89*10^{-4} \ mol \ Pb[/tex]
There are 7.89*10⁻⁴ moles of lead in 4.75*10²⁰ atoms of lead.
