Balanced reaction equation:
2Al + 3CuSO4 = 3Cu + Al2(SO4)3
Molar weight of Al: 26.98 g/mol
Quantity of Al: 10.45 g / 26.98 g/mol = 0.387 mol
Molar weight of CuSO4: 159.61 g/mol
Quantity of CuSO4: 66.55 / 159.61 g/mol = 0.417 mol
According to balanced equation, the ratio of reactants is 2 : 3.
So, aluminium is in excess.
Mass of copper must be calculated from quantity of copper sulfate:
Quantity of Cu (is the same as copper sulfate): 0.417 mol
Molar weight of Cu: 63.55 g/mol
Mass of Cu: 0.417 mol * 63.55 g/mol = 26.5 g
Answer: a) aluminium; b) 26.5 g