To calculate the mass of 0.125 mol of copper (II) oxide, we need to know its molar mass. The molar mass of copper (II) oxide (CuO) can be calculated by adding the atomic masses of copper and oxygen.

The atomic mass of copper (Cu) is 63.55 g/mol, and the atomic mass of oxygen (O) is 16.00 g/mol.

The molar mass of CuO = (1 × 63.55 g/mol) + (1 × 16.00 g/mol) = 79.55 g/mol.

Now, we can calculate the mass of 0.125 mol of CuO by multiplying the number of moles by the molar mass:

Mass of CuO = (0.125 mol) × (79.55 g/mol) = 9.944 g

Therefore, the mass of 0.125 mol of copper (II) oxide is 9.944 g.