1. Find the molar mass of copper (Cu):

* Look up the atomic mass of copper on the periodic table. It's approximately 63.55 g/mol.

2. Use the formula:

* mass (g) = moles × molar mass (g/mol)

3. Plug in the values:

* mass (g) = 0.0420 mol × 63.55 g/mol

4. Calculate:

* mass (g) ≈ 2.67 g

Therefore, the mass of 0.0420 moles of copper is approximately 2.67 grams.