# What is the mass of #1.2*10^18# formula units of calcium chloride?

##### 1 Answer

#### Answer:

#### Explanation:

The thing to keep in mind about formula units is that you need **mole** of an ionic compound **Avogadro's constant** here.

In this case, you know that **mole** of calcium chloride.

Moreover, you know that calcium chloride has a **molar mass** of **mole** of calcium chloride has a mass of

So if **mole** of calcium chloride contains **formula units** and has a mass of **formula units** of calcium chloride have a mass of

This means that your sample has a mass of

#1.2 * 10^8 color(red)(cancel(color(black)("f. units CaCl"_2))) * "110.98 g"/(6.022 * 10^(23)color(red)(cancel(color(black)("f. units CaCl"_2)))) = color(darkgreen)(ul(color(black)(2.2 * 10^(-4) quad "g")))#

The answer is rounded to two **sig figs**, the number of sig figs you have for the number of formula units.