1. Find the molar mass of copper:

* The molar mass of copper (Cu) is 63.55 g/mol. This means one mole of copper weighs 63.55 grams.

2. Use the formula:

* mass = moles × molar mass

3. Plug in the values:

* mass = 0.0420 moles × 63.55 g/mol

4. Calculate the mass:

* mass = 2.67 grams

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