Find the mass and volume of oxygen that was required to burn copper if 4 g of copper (ii) oxide was formed.

1. Let’s write down the reaction equation:

2Cu + O2 = 2CuO.

2. Find the amount of the formed copper oxide:

n (CuO) = m (CuO) / M (CuO) = 4 g / 64 g / mol = 0.0625 mol.

3. According to the reaction equation, we find the amount of reacted oxygen, and then its mass and volume (Vm is the molar volume, constant equal to 22.4 l / mol):

n (O2) = n (CuO) / 2 = 0.0625 mol / 2 = 0.031 mol.

m (O2) = n (O2) * M (O2) = 0.031 mol * 32 g / mol = 1 g.

V (O2) = n (O2) * Vm = 0.031 mol * 22.4 L / mol = 0.7 L.

Answer: m (O2) = 1 g; V (O2) = 0.7 l.