# How many moles of nickel are in 5.12 * 10^25 atoms of nickel?

Feb 9, 2018

$85.0$

#### Explanation:

The key here is Avogadro's constant, which tells you the number of representative particles present in $1$ mole of a substance.

By definition, and this is what Avogadro's constant tells you, $1$ mole of nickel must contain $6.022 \cdot {10}^{23}$ atoms of nickel. In other words, if you don't have $6.022 \cdot {10}^{23}$ atoms of nickel, you don't have $1$ mole of nickel.

Now, your sample contains $5.12 \cdot {10}^{25}$ atoms of nickel, so you know for a fact that the sample contains more than $1$ mole of nickel.

To find the exact number of moles, set up a conversion factor using Avogadro's constant.

$5.12 \cdot {10}^{25} \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{atoms Ni"))) * "1 mole Ni"/(6.022 * 10^(23)color(red)(cancel(color(black)("atoms Ni")))) = color(darkgreen)(ul(color(black)("85.0 moles Ni}}}}$

The answer must be rounded to three sig figs, the number of sig figs you have for the number of atoms present in the sample.