a couple of pennies have a mas of 5.2 grams. Asuming that the pennies are 100% percent copper, how many moles of copper are the pennies

5.2g copper (Cu) => 0.082 moles copper (2 sig.figs.)

Explanation:

mole conversions:

grams to moles => divide by formula wt.

moles to grams => multiply by formula wt.

gas volumes to moles => divide volume by 22.4Liters/mole (STP conditions only)

This problem:

mass to moles => divide by formula wt.

mass = 5.2g = 5.2g/63.5g/mole = 0.082 moles copper (2 sig.figs.)