# Question #8cba1

##### 1 Answer

#### Explanation:

You can;t go from *grams* to *atoms* without going through **moles8* first, so start by converting the mass of calcium to moles.

To do that, use the **molar mass** of calcium.

#"36,700" color(red)(cancel(color(black)("g"))) * "1 mole Ca"/(40.078 color(red)(cancel(color(black)("g")))) = "915.71 moles Ca"#

Now, in order to go from *moles* to *atoms*, use the fact that, by definition, **mole** of calcium must contain **atoms** of calcium **Avogadro's constant**.

In other words, for every **atoms** of calcium you have in your sample, you have **mole** of calcium.

This implies that your sample will contain

#915.71 color(red)(cancel(color(black)("moles Ca"))) * (6.022 * 10^(23)color(white)(.)"atoms Ca")/(1color(red)(cancel(color(black)("mole Ca")))) = color(darkgreen)(ul(color(black)(5.51 * 10^(26)color(white)(.)"atoms Ca")))#

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