# Question #4dd5f

##### 1 Answer

#### Explanation:

For starters, it's worth pointing out that you're not dealing with *molecules* of iron(III) fluoride here because this compound is **ionic**.

So a more accurate statement here would be that the problem wants you to find the number of **formula units** of iron(III) fluoride present in that sample.

Now, the key here is the **molar mass** of iron(III) fluoride, which you will find listed as

Since you know that the molar mass of the compound tells you the mass of exactly **mole** of iron(III) fluoride, you can say that you will get **mole** of iron(III) fluoride present in your sample.

You should also know that **Avogadro's constant** tells you that you need **formula units** of iron(III) fluoride in order to have **mole** of this compound.

So if you know that **mole** contains **formula units** and has a mass of

#24 color(red)(cancel(color(black)("g"))) * (6.022 * 10^(23) quad "formula unit FeF"_3)/(112.84color(red)(cancel(color(black)("g")))) = color(darkgreen)(ul(color(black)(1.3 * 10^(23) quad "formula units FeF"_3)))#

The answer is rounded to two **sig figs**, the number of sig figs you have for the mass of iron(III) fluoride.