chem alevel aqa question

A passenger jet contains 4050 kg of copper wiring.
A rock sample contains 1.25% CuFeS2 by mass.
Calculate the mass, in tonnes, of rock needed to produce enough copper wire for a passenger jet. (1 tonne = 1000 kg)

the answer is 936 tonnes but i don't get why
So I think the easiest way to do this is to first take the Mr of CuFeS2 which is 183.5. The atomic mass of copper is 63.5. So we can find the proportion of the CuFeS2 which is useable to make copper wire using this. (63.5 / 183.5 = 0.346).
We already know that 1.25% of the rock contains CuFeS2, but only 34.6% of this can be used to make wire. We can find the proportion of the rock useable to make copper wire by combining these two proportions (0.346 * 0.0125 = 0.004325).

4050 kg of wiring is needed for the jet, so we can solve form an equation using the information you just got from above, x will be the amount of rock, but we need to factor in that only 0.4325% of this is useable (0.004325 as a decimal).

0.004325x = 4050 kg

Solving this you get x = 4050 / 0.004325 = 936416 kg = 936.416 tonnes (936 to 3 s.f.)
thank you so much you explained this really well
Original post by ricecakes1
thank you so much you explained this really well

Happy to help