# How many molecules of aspirin are contained in a 100.0 g tablet of aspirin, #C_9H_8O_4#?

##### 1 Answer

#### Explanation:

Your strategy her will be to

use themolar massof aspirin to determine how manymolesyou have in that sampleuseAvogadro's numberto convert the number of moles tonumber of molecules

So, aspirin, **one mole** of aspirin will have a mass of

You're dealing with a

#100.0 color(red)(cancel(color(black)("g"))) * "1 mole aspirin"/(180.157color(red)(cancel(color(black)("g")))) = "0.55507 moles aspirin"#

Now that you know how many moles of aspirin you have in your sample, use the fact that **one mole** of a substance contains **Avogadro's number**.

#color(purple)(|bar(ul(color(white)(a/a)color(black)("1 mole" = 6.022 * 10^(23)"molcules")color(white)(a/)|))) -># Avogadro's number

Use Avogadro's number as a *conversion factor* to calculate how many molecules you get in

#0.55507color(red)(cancel(color(black)("moles"))) * (6.022 * 10^(23)"molecules")/(1color(red)(cancel(color(black)("mole")))) = color(green)(|bar(ul(color(white)(a/a)3.343 * 10^(23)"molecules"color(white)(a/a)|)))#

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