# How many copper atoms are in 2.15 g of copper?

Aug 12, 2016

There are 2.04 × 10^22color(white)(l) "Cu atoms".

#### Explanation:

You could use the known atomic mass of $\text{Cu}$ (63.456 u) to calculate the percentages of each isotope, but that's the hard way.

The easy way is to calculate the number of atoms with an average mass of 63.546 u.

A mole of these atoms has a mass of 63.546 g.

"No. of atoms" = 2.15 color(red)(cancel(color(black)("g Cu"))) × (1 color(red)(cancel(color(black)("mol Cu"))))/(63.456 color(red)(cancel(color(black)("g Cu")))) × (6.022 × 10^23 "Cu atoms")/(1 color(red)(cancel(color(black)("mol Cu"))))

= 2.04 × 10^22 color(white)(l)"Cu atoms"