How many copper atoms are in 5.00 g of copper wire, given Cu = 63.55 g/mol and 6.022 x 10^23 atoms per mole?

1. Getting from mass to a count of atoms takes two steps, mass to moles and then moles to atoms. 2. Step one: 5.00 g / 63.55 g/mol = 0.07868 mol of copper. 3. Step two: 0.07868 mol x 6.022 x 10^23 atoms/mol. 4. The product is 4.74 x 10^22 atoms of copper. 5. Units cancel cleanly, since grams cancel in step one and moles cancel in step two. 6. As a check, 5.00 g is a bit less than a tenth of 63.55 g, so the count should be near a tenth of Avogadro's number. 7. The value 7.66 x 10^24 atoms comes from multiplying by the molar mass instead of dividing by it. _Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.1 Formula Mass and the Mole Concept_