Solution: In 100g of the75wt%Cu-25wt%Ni alloy, there are 75g of Cu
and 25g of Ni.
Number of gram-mol of Cu = 75g / 63.54g/mol = 1.1803 mol
Number of gram-mol of Ni = 25g / 58.69g/mol = 0.4260 mol
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Total gram-moles = 1.6063 mol
Cu at% = (1.1803mol / 1.6063mol)(100%) = 73.5at%
Ni at% = (0.4260mol / 1.6063mol)(100%) = 26.5at%