# How many molecules of nitrogen monoxide are in a 22.5 gram sample?

##### 1 Answer

#### Explanation:

Your strategy here will be to use the **molar mass** of *nitric oxide*, **moles** you get in that sample.

Once you know that, you can use **Avogadro's number** as a *conversion factor* to help you determine how many *molecules* would be present in that many moles.

So, nitric oxide has a molar mass of **one mole** of nitric oxide has a mass of

Since your sample is about *one mole*, you can say for a fact that you're dealing with **less than one mole** of nitric oxide.

More precisely, you will have

#22.5 color(red)(cancel(color(black)("g"))) * " 1 mole NO"/(30.01 color(red)(cancel(color(black)("g")))) = "0.7498 moles NO"#

Now, according to **Avogadro's number**, one mole of any substance contains

#0.7498 color(red)(cancel(color(black)("moles NO"))) * overbrace((6.022 * 10^(23)"molec. NO")/(1color(red)(cancel(color(black)("mole NO")))))^(color(purple)("Avogadro's number")) = "4.5153 molec. NO"#

Rounded to three **sig figs**, the number of sig figs you have for the mass of nitric oxide, the answer will be

#"no. of molecules" = color(green)(|bar(ul(color(white)(a/a)4.52 * 10^(23)color(white)(a/a)|)))#