According to law of conservation of mass, mass can neither be destroyed nor created in a chemical reaction. Thus, sum of masses of reactants must be equal to sum of masses of products in a reaction.
The chemical reaction is as follows:
Here, sum of masses of Cu and oxygen gas should be equal to CuO formed.
Thus, mass of oxygen will be:
This can be further proved as follows:
The balanced chemical reaction is as follows:
Here, 2 moles of Cu completely reacts with 1 mole of to give 2 moles of
.
Thus, 1 mole of Cu reacts with 0.5 moles of .
The mass of Cu is 508.4 and molar mass is 63.546 g/mol, number of moles can be calculated as follows:
Thus, number of moles of reacting will be:
Molar mass of oxygen molecule is 32 g/mol thus, mass can be calculated as follows:
m=n×M=4 mol×32 g/mol=128 g/mol
This satisfies the law of conservation of mass.