Question

Question #8cba1

Answer 1

`5.51 * 10^(26)`

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, `1` mole of calcium must contain `6.022 * 10^(23)` atoms of calcium `->` this is known as Avogadro's constant.

In other words, for every `6.022 * 10^(23)` atoms of calcium you have in your sample, you have `1` 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.