A length of copper wire has a mass of 7.29 g. How many moles of copper are in the wire?

Question

A length of copper wire has a mass of 7.29 g. How many moles of copper are in the wire?

Answer 1

We need to use our friendly periodic table as it gives us a direct relationship between grams and moles of atoms!

So the first thing we need to do is to locate copper on the periodic table and to find its atomic mass, which is listed in units of amu, which are grams per moles (g/mol). Copper uses the symbol Cu so on my periodic table, Cu has an atomic mass of 63.55 g/mol (this can vary slightly from one periodic table to another so us the number that you see on yours!)

This means that for every 1 mole of Copper, I have to have 63.55 grams of copper. We seem to have less than a mole as we were told that our copper wire weighs 7.29 grams. So how about we figure out how many moles we have by using our atomic or molar mass as a conversion factor?

We always start with what we know so 7.29 grams of copper x 1 mole of copper

63.55 grams of copper

The units of grams of copper will cancel each other out, and we will be left with the amount of moles of copper that are in the copper wire!

Answer 2

molar mass of copper = 63.55 g/mol

7.29 g copper x (1 mol copper/63.55 g copper) = 0.115 mol copper