Answer
The mass of chalcocite=362.5 pounds
Work Step by Step
Molar mass of Cu=63.546amu
The molar mass of chalcopyrite=183.52
The molar mass of chalcocite=159.16
First, we calculate the percent composition of copper in chalcopyrite using the formula:
Percent composition of copper=$\frac{\text{molar mass copper}}{\text{molar mass of chalcopyrite}}\times100=\frac{63.546}{183.52}\times100\approx34.63\%$
Then we calculate the mass of copper in 418 pounds of chalcopyrite using the formula:
Mass of copper=mass of chalcopyrite$\times$percent composition of copper
Mass of copper=$418\times34.63\%\approx144.75 pounds$
The percent composition of copper in chalcocite:
Percent composition of copper=$\frac{\text{molar mass copper}}{\text{molar mass of chalcocite}}\times100=\frac{63.546}{159.16}\times100\approx39.93\%$
Let the mass of chalcocite be $x$
Mass of copper=mass of chalcocite$\times$percent composition of copper
$144.75=x\times39.93\%$
$x=\frac{144.75}{39.93\%}\approx362.5 pounds$
The mass of chalcocite=362.5 pounds
