1. Find the molar mass of CO2:

* Carbon (C) has a molar mass of 12.01 g/mol

* Oxygen (O) has a molar mass of 16.00 g/mol

* CO2 has one carbon and two oxygen atoms: 12.01 + (16.00 x 2) = 44.01 g/mol

2. Multiply the molar mass by the number of moles:

* 44.01 g/mol * 4 mol = 176.04 g

Therefore, the mass of 4 moles of CO2 is 176.04 grams.