Question

How many atoms are in 153 g of calcium?

Answer 1

`2.30 xx 10^24` `"atoms Ca"`

Explanation:

We're asked to calculate the number of atoms of `"Ca"` in `153` `"g Ca"`.

What we must first do is convert the given mass of calcium to moles of calcium, using its molar mass (referring to a periodic table, this is `40.08"g"/"mol"`):

`153` `cancel("g Ca")((1"mol Ca")/(40.08cancel("g Ca"))) = color(blue)(3.82` `color(blue)("mol Ca"`

Using Avogadro's number, `6.022 xx 10^23"particles"/"mol"`, we can calculate the number of atoms present:

`color(blue)(3.82` `cancel(color(blue)("mol Ca"))((6.022xx10^23"atoms Ca")/(1cancel("mol Ca")))`

`= color(red)(2.30 xx 10^24` `color(red)("atoms Ca"`