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The compositions in atom% of an alloy that consists of 97 wt% Al and 3 wt% Cu are:

Select one:

A. 98.7 at% Al & 1.3 at% Cu
B. 97.8 at% Al & 2.2 at% Cu
C. 99.7 at% Al & 0.3 at% Cu
D. 89.7 at% Al & 10.3 at% Cu
E. 95.7 at% Al & 4.3 at% Cu

Answer :

The compositions in atom% of an alloy that consists of 97% wt% Al & 3 wt% Cu are 98.7 at% Al & 1.3 at% Cu. Option a is the correct answer.

The atomic mass of aluminum is 26.98 g/mol and the atomic mass of copper is 63.55 g/mol. So, in a 97% wt% Al alloy, there are 97/26.98 = 3.63 moles of aluminum for every 3/63.55 = 0.04 moles of copper.

This means that the atom fraction of aluminum is 3.63 / (3.63 + 0.04) = 98.7. The atom fraction of copper is then 0.04 / (3.63 + 0.04) = 1.3.

Option a is the correct answer.

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