Question

The wt.% (correct to two decimal places) of Cu in chalcopyrite (CuFeS₂) (atomic weight of Cu = 63.55, Fe = 55.85, S = 32.07) is ........

Hint:

To calculate the weight percentage of an element in a compound, divide the atomic weight of the element by the molar mass of the compound, and multiply by 100.

Answer 1

Correct Answer: 34.6

Step 1: Find the molar mass of CuFeS₂. 
We know the atomic masses of Cu, Fe, and S: \[ \text{Molar mass of CuFeS₂} = \text{Atomic mass of Cu} + \text{Atomic mass of Fe} + (2 \times \text{Atomic mass of S}) \] Substitute the given atomic masses: \[ \text{Molar mass of CuFeS₂} = 63.55 + 55.85 + (2 \times 32.07) = 63.55 + 55.85 + 64.14 = 183.54 \, \text{g/mol} \]

Step 2: Calculate the weight percentage of Cu. 
The weight percentage of Cu in chalcopyrite is calculated as: \[ \text{wt.\% of Cu} = \left( \frac{\text{Atomic weight of Cu}}{\text{Molar mass of CuFeS₂}} \right) \times 100 \] 

Substituting the values: \[ \text{wt.\% of Cu} = \left( \frac{63.55}{183.54} \right) \times 100 = 34.64\% \] 

Thus, the weight percentage of Cu in chalcopyrite is 34.64%.