Question

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

Answer 1

`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 * 10^(23)` atoms of nickel. In other words, if you don't have `6.022 * 10^(23)` atoms of nickel, you don't have `1` mole of nickel.

Now, your sample contains `5.12 * 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 * 10^(25) color(red)(cancel(color(black)("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.