Answer
There is 0.013 mole of $Cu$ in $7.8 \times 10^{21}$ atoms of that.
Work Step by Step
1. State the data and objective:
$7.8 \times 10^{21}$ atoms of $Cu$
Objective: Number of Cu moles.
2. Identify the conversion factor.
Using Avogadro's number:
1 mole $(X)$ $= 6.02 \times 10^{23}$ $(X)$ $atoms$
$\frac{1 mole (X)}{6.02 \times 10^{23} atoms (X)}$ and $\frac{6.02 \times 10^{23} atoms (X)}{1 mole (X)}$
3. Use the conversion factor and the data to calculate the number of Cu moles:
$7.8 \times 10^{21} atoms (Cu) \times \frac{1 mole (Cu)}{6.02 \times 10^{23} atoms (Cu)} = 0.013mole(Cu) $
