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# AS Chem Moles Calculation watch

1. A passenger jet contains 4050kg 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 the passenger jet.

8CuFeS2 + 19O2 + 8SiO2 = 2Cu2S + 2Cu2O + 14SO2 + 8FeSiO3

1Cu2S + 2Cu2O = 6Cu + SO2

So the molar ratio is 8 : 6

4,050,000 / 63.5 = 63779mol Cu
(63779 / 6) * 8 = 85039mol CuFeS2

85039 * (63.5 + 55.8 + (32*2)) = 15,587,648g CuFeS2

15,587,648 * 100 / 1.25 = 1,247,011,840g = 1247 tonnes

Is this correct because everyone said it should be 624 tonnes, but i checked my method over and over and cant find any mistakes
2. (Original post by Viren123)
A passenger jet contains 4050kg 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 the passenger jet.

8CuFeS2 + 19O2 + 8SiO2 = 2Cu2S + 2Cu2O + 14SO2 + 8FeSiO3

1Cu2S + 2Cu2O = 6Cu + SO2

So the molar ratio is 8 : 6

4,050,000 / 63.5 = 63779mol Cu
(63779 / 6) * 8 = 85039mol CuFeS2

85039 * (63.5 + 55.8 + (32*2)) = 15,587,648g CuFeS2

15,587,648 * 100 / 1.25 = 1,247,011,840g = 1247 tonnes

Is this correct because everyone said it should be 624 tonnes, but i checked my method over and over and cant find any mistakes
Ugh this was my exam question I remember the nightmare. I’ll look over it and see if I can see anything wrong, but I got around 1000 tonnes as well and I think I was wrong...
3. I think it’s the molar ratio that seems incorrect, all of your calculations look right. My only reasoning is that you produce 2 moles of Cu2S and you only need one
4. I think many assumed a 1:1 molar ratio so ended up with 963 tonnes. But then people that used the equations to work out the molar ratio ended up with 624 tonnes, which is less. This isnt possible because the Cu has to come from somewhere (You cant have a molar ratio greater than 1:1)
5. (Original post by TheMythicalBeast)
I think it’s the molar ratio that seems incorrect, all of your calculations look right. My only reasoning is that you produce 2 moles of Cu2S and you only need one
But you need 2 moles of Cu2O, so the Cu2S has to be in excess
6. (Original post by Viren123)
But you need 2 moles of Cu2O, so the Cu2S has to be in excess
I’m just thinking what if you combined the equations first to get:

8CuFeS2 + 19O2 + 8SiO2 —> Cu2S + 14SO2 + 8FeSiO3 + 6Cu

And here’s where I realised it doesn’t matter because it doesn’t change the amount of moles of pure copper that you get... Well I’ll keep trying :/ Try to work backwards from their answer

Edit: looks like the only thing that you’re missing to get the right answer is to half yours, i’m just not sure why
7. I think their answer was wrong them because they got the molar ratio as 1.5mol Cu for every 1mol CuFeS2, which is impossible. Thanks for the help! Also have you done A2? How does it compare to AS? And what is the hardest topic you found at AS and A2?

Im a GCSE chem student just doing this for fun and at AS im finding it easier than some of the GCSEs i do like english and german because I find Chemistry just makes sense for me and I can answer the questions correctly. So i was wondering if A2 is a big step up from AS
8. (Original post by Viren123)
I think their answer was wrong them because they got the molar ratio as 1.5mol Cu for every 1mol CuFeS2, which is impossible. Thanks for the help! Also have you done A2? How does it compare to AS? And what is the hardest topic you found at AS and A2?

Im a GCSE chem student just doing this for fun and at AS im finding it easier than some of the GCSEs i do like english and german because I find Chemistry just makes sense for me and I can answer the questions correctly. So i was wondering if A2 is a big step up from AS
I’ve just tried an online balancing equations website to see if the equation wasn’t balanced correctly and it won’t even balance it... can’t find it anywhere else either, which is a bit weird. It comes up with a version without Cu2O. Basically if you saw the paper you know we were asked to balance the equation first and I think some people got 8:6 (or 1:0.75) and some got 8:12 (or 1:1.5), which gives you the two answers. Since the equation itself seems wrong from my quick google search, I wouldn’t trust any of the answers...

Anyway, you’re welcome for he help Yes, I’m doing A2 and it is a bit more difficult than AS but mostly in a way where it’s as if you took an AS topic and doubled it by adding stages. I haven’t found one that I found particularly difficult yet, but some is quite ridiculous like having to remember colours, solvents and reactions of different icons and then remembering how to test for everything it’s just impossible. A topic you may find not too difficult to understand but difficult to learn is Aromatics, because as my teacher said, textbooks often don’t talk about it much because no one is sure what names or reactions we’re supposed to be using exactly, they didn’t specify

Overall the step up isn’t really big, definitely not bigger than the GCSE to AS. If Chemistry just clicks for you then I’d recommend continuing doing it, even if that’s not what you want to do in uni. That’s what happened with maths for me and it might just about score me an easy (for me at least) A*, which will be useful in uni applications
9. I think I know where people are getting the 600 tonnes from. Basically if you balance the equations you get:

4CuFeS2 + 9.5O2 + 4SiO2 —> Cu2S + Cu2O + 7SO2 + 4FeSiO3
Cu2S + 2Cu2O —> 6Cu + SO2

These are what you got, but the top one is simplified and it’s the answer you would usually get doing it from experience as we do usually put O2 in fraction in the simplest eq and you’d balance O2 last as it has the most atoms here (so you’d do the CuFeS2, then FeSiO3 as it’s the second simplest, then balance the Si, then the S, then the O). Anyway, I think this would lead some students to believe it’s 4:6 without realising you need to go through the reaction twice to get the 2 molecules of Cu2O that you need so it’s actually 8:6
10. I am in the same boat as you, I used the same method and got 1248 tonnes...

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Updated: March 7, 2018
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