Question

A recipe for chili calls for 3 g of sodium chloride. How many formula units of `NaCl` is that?

Answer 1

`3` `g` is `0.075` `mol` of `NaCl`. Multiply this by Avogadro's number to find that this amount of salt contains `4.5xx10^22` formula units of `NaCl`.

Explanation:

First find the number of moles.

The molar mass is `23+17=40` `gmol^-1`, so `n=m/M=3/40=0.075` `mol`.

Now one mole of any substance contains Avogadro's number, `6.02xx10^23` units of that substance: in this case formula units (one `Na` and one `Cl`) of `NaCl`.

That means the `3` `g` of salt (and therefore the chili) will contain `4.5xx10^22` formula units of `NaCl`.