Answer :
The correct option is d. 98.7 at% Al & 1.3 at% Cu. To find the atom% composition of an alloy consisting of 97% wt% Al and 3% wt% Cu, we calculate the moles of each element and then their respective percentages out of the total moles.
The composition in atom percent (at%) of an alloy that consists of 97% wt% Al and 3 wt% Cu requires using the atomic weights of Al and Cu to convert from weight percent to atom percent. First, we must find the number of moles of each element by using their respective atomic weights:
- Atomic weight of Al = 27.0 g/mol
- Atomic weight of Cu = 63.55 g/mol
Next, calculate the moles of each in 100g of the alloy:
- Moles of Al = 97 g / 27.0 g/mol = 3.59 moles
- Moles of Cu = 3 g / 63.55 g/mol = 0.0472 moles
To convert these to atom percent, we need to find the total number of moles and calculate the percentage of each:
- Total moles = 3.59 moles Al + 0.0472 moles Cu = 3.6372 moles
- Atom percent of Al = (3.59 moles Al / 3.6372 total moles) * 100 = 98.7 at%
- Atom percent of Cu = (0.0472 moles Cu / 3.6372 total moles) * 100 = 1.3 at%
Therefore, the correct option is d. 98.7 at% Al & 1.3 at% Cu.