##22″g Cu”## contains ##2.1 xx 10^23## atoms of Cu.

In order to solve this problem, you need to determine the molar mass of copper, which is the mass of one mole of copper. The molar mass of copper is its atomic weight on in g/mol, and is ##”63.546g/mol”##. You also need to know that one mole of copper contains ##”6.022 x 10″^23## atoms of copper. With this information you can solve this problem using dimensional analysis. You will convert given mass to moles, and moles to atoms.

##22cancel”g Cu” xx (1 cancel”mol Cu”)/(63.546cancel”g Cu”)xx(6.022 xx 10^23 “atoms Cu”)/(1 cancel”mol Cu”)=2.1 xx 10^23 “atoms Cu”##

The moles and grams cancel, leaving number of atoms.

##22″g Cu”## contains ##2.1 xx 10^23## atoms of Cu.