[yyal]

hey i'm stuck on a chem question and i need help please =]
the question is

A 4.0g sample of copper ore contains 0.12 g of copper pyrites, CuFS₂. Calculate the percentage by mass of copper in the ore...

isn't it just mass of 1 mole of element in the compound divide by the mass of 1 mole of the compound times 100?
i'm confuse here ==
please help.. thanks!!
the answer says its 1.0% i dun get how they got that

[DaAzNkIgGa627]

You basically have to find the percentage of the copper in the copper pyrites, and then what percentage the copper pyrite is of the copper ore.

For example

.12 g / 4 g = .03 (that means 3 percent of the ore is copper pyrite)

The molar mass of the copper pyrite is the molar weights of Cu + F + S2. So 146.69 grams is 1 mole of copper pyrite.

To find what percentage of copper pyrite is copper you have to divide the molar weight of copper to copper pyrite

63.55 g / 146.69 g = .43 (43 percent)

So 3 percent of the copper ore is copper pyrite. 43 percent of the copper pyrite is copper.

.03 * .43 = .0129

1.29 percent is copper from the copper pyrite.

Hope that helps