# The molar mass of copper(II) chloride, #"CuCl"_2#, is #"134 g/mol"#. How many formula units of #"CuCl"_2# are present in #"17.6 g"# of #"CuCl"_2#?

##### 1 Answer

#### Explanation:

The problem provides you with the **molar mass** of copper(II) chloride, *formula units* are present in a **Avogadro's number**.

According to **Avogadro's number**, which is essentially the definition of the *mole*, a **mole** of an ionic compound contains **formula units** of that compound.

This means that your strategy here will be to use the **molar mass** to convert the sample to *moles*, then use Avogadro's number to convert the moles to formula units.

Your sample contains

#17.6 color(red)(cancel(color(black)("g"))) * "1 mole CuCl"_2/(134color(red)(cancel(color(black)("g")))) = "0.13134 moles CuCl"2#

Now use Avogadro's number to figure out how many formula units would be present in that many moles

#0.13134 color(red)(cancel(color(black)("moles CuCl"_2))) * (6.022 * 10^(23)"f. units")/(1color(red)(cancel(color(black)("mole CuCl"_2)))) = color(green)(|bar(ul(color(white)(a/a)color(black)(7.91 * 10^(22)"f. units")color(white)(a/a)|)))#

The answer is rounded to three **sig figs**, the number of sig figs you have for the mass of the sample.