Question

Bronze is a solid alloy of 88% copper and 12% tin by mass. Brass is an alloy of 95% copper and 5% zinc by mass. Calculate the mole fraction of copper when 100 g of each alloy is mixed together.
(Molar mass of copper = 63.5 g/mol, molar mass of tin = 119 g/mol and molar mass of zinc = 65.5 g/mol)

• A. 0.94
• B. 0.73
• C. 0.6
• D. 0.88

Answer 1

The correct option is A 0.94

Amount of copper present in 100 g of bronze = 88 g
Amount of tin present in 100 g of bronze = 12 g
Amount of copper present in 100 g of brass = 95 g
Amount of zinc present in 100 g of brass = 5 g
Now, 100 g of each bronze and brass solution are mixed together
Amount of copper in resulting solution = 183 g
Amount of tin in resulting solution = 12 g
Amount of zinc in resulting solution = 5 g
Number of moles of a component = $\frac{\text{given mass}}{\text{molar mass}}$
Moles of copper = $\frac{183}{63.5}$ = 2.88 mol
Moles of tin = $\frac{12}{119}$ = 0.10 mol
Moles of zinc = $\frac{5}{65.5}$ = 0.08 mol
Mole fraction = $\frac{\text{number of moles of copper in the mixture}}{\text{total number of moles in the mixture}}$
Mole fraction = $\frac{2.88}{2.88+0.10+0.08}$ = 0.94