Final answer:
The composition, in weight percent, of an alloy that consists of 5 at% Cu and 95 at% Pt is 1.42% Cu and 98.58% Pt.
Step-by-step explanation:
An alloy that consists of 5 at% Cu and 95 at% Pt means that for every 100 atoms in the alloy, 5 of them are of Cu and 95 of them are of Pt. To find the weight percent of each element, we need to convert the atomic percentages into weight percentages. To do this, we need to consider the molar masses of Cu (63.55 g/mol) and Pt (195.08 g/mol).
To find the weight percent of Cu, we multiply the atomic percent of Cu by the molar mass of Cu and divide it by the total molar mass of the alloy. In this case, the weight percent of Cu is calculated as (5/100) * (63.55 g/mol) / (5/100 * 63.55 g/mol + 95/100 * 195.08 g/mol) * 100% = 1.42%.
The weight percent of Pt can be calculated similarly, but as the atomic percent of Pt is 95, the weight percent of Pt is (95/100) * (195.08 g/mol) / (5/100 * 63.55 g/mol + 95/100 * 195.08 g/mol) * 100% = 98.58%.