Question

How many moles of sulfur hexafluoride are present in 2.56E21 molecules of this compound?

Answer 1

That many sulfur hexafluoride, or `SF_6`, molecules are equivalent to 0.00425 moles.

You know that 1 mole of any compound contains `6.022 * 10^(23)` molecules of that compound - this is known as Avogadro's number. SInce you have less that that number of molecules of sulfur hexafluoride to work with, you'll have less than 1 mole.

So, the exact number of moles you have is

`2.56 * 10^(21)"molecules" * "1 mole"/(6.022 * 10^(23)"molecules") = 0.4251 * 10^(-2) = "0.00425 moles"`

The answer is rounded to three sig figs, the number of sig figs you have in `2.56 * 10^(21)`.