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Chemistry percentage composition HARD. (1 Viewer)

imxprt

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Hey can anyone help me with this question.
A steel company requires 2 tonnes of Fe. the company decided to mine from a site containing goethite. FeO(OH). which contains 31% of the mineral. how much of the goethite needs to be mined to obtain 2 tonnes of Fe.
 

CM_Tutor

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Goethite, FeO(OH), being 31% Fe means that the m(Fe) makes up 31% of m(goethite):

m(Fe) = 31% x m(goethite)

So, if I wanted 500 g Fe (say), then I would need to solve:

500 = 0.31 x m(goethite)

m(goethite) = 500 / 0.31 = 1612.9 ... g = 1.61 kg

Now, you want m(Fe) to be 2 tonne = 2000 kg, so ...
 

dumNerd

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Hey can anyone help me with this question.
A steel company requires 2 tonnes of Fe. the company decided to mine from a site containing goethite. FeO(OH). which contains 31% of the mineral. how much of the goethite needs to be mined to obtain 2 tonnes of Fe.
You baited me tf
 

Eagle Mum

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The question seems somewhat ambiguous - have you typed it correctly?

The percentage by mass of Fe in the mineral goethite is fixed at 62.85% (=55.845/(55.845+2x15.999+1.008)), so it doesn’t matter what percentage of the rock is goethite, since you would need 2000 / 0.6285 kg (3182 kg) of goethite to extract 2000 kg of iron. Therefore, I don’t see how the 31% is relevant.

You would need to mine 2000 / (0.6285 x 0.31) = 10 265 kg of iron ore (mixture of iron compounds with sand & clay) to extract 2000 kg of iron.
 

Eagle Mum

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Yeah this is the question
In your working out, x (=2000/(0.6285x0.31)) is the required mass of iron ore, whereas 2000/0.6285 is the required mass of goethite.
My sympathies - test/exam questions ought to be rigorously set.
 

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