Question

How many atoms of copper are in a pure copper penny that weighs 2.15 g? (1 amu = 1.6605 10-24 g)

Answer 1

How many atoms of copper are in a pure copper penny that weighs 2.15 g?

(1 amu = 1.6605 10-24 g).

**Solution:**

1 mole of substance include $6.02 \cdot 10^{23} \, \text{mol}^{-1}$ atoms (Avogadro's constant=1/1.6605 $10^{-24} \, \text{g}$). The weight of 1 mole Copper is 63.546 g. Consequently, 63.546 g of Copper include $6.02 \cdot 10^{23}$ atoms and 2.15 g of Copper include:

$$N = \frac{2.15 \cdot 6.02 \cdot 10^{23}}{63.546} = 2.04 \cdot 10^{22} \text{ atoms}$$

**Answer:** N(Cu)=2.04·10²² atoms.