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Simple Stoic Qustion.........

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bucket:
Its been so long since I've done chem..

"Iron metal is extracted in a blast furnace by a reaction between iron(III) oxide and carbon monoxide: Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g)
To produce 1000kg of iron, calculate the mass of the iron(III) oxide required"

I used to find stoichiometry sooo easy  :'( too many beers over the holidays...

enwiabe:
Alright, so let's look at the molar ratios.

1 Fe2O3: 3 CO : 2 Fe : 3 CO2

You're given that 1000kg of iron is produced (1000kg = 1,000,000 grams)

You know that n = m/M. I assume you're familiar with this equation. If not, n = mole of substance, m = mass (in g) of substance, M = Molar Mass (g/mol) of substance.

 from memory M(Fe) = 55.9 (could be wrong, i don't have a periodic table on me)

therefore, n(Fe) = m(Fe)/M(Fe), therefore, n(Fe) = 1000000/55.9 ~ 17889.088 mol (stored on calculator).

Now, if you have 17889.088 mol of Fe, and for every 1 mol of Fe2O3, you obtain 2 mol of Fe, then to produce 17889.088 mol you need to HALVE 17889.088 mol, to obtain ~ 8944.54 mol of Fe2O3. Because, for every 1 mol of Fe2O3 consumed, 2 mol of Fe is produced. Hence, 8944.54 mol of Fe2O3 produced double the amount (17889.088 mol) of Fe.

Now that you have the mol you've gotta sub back into the equation, n(Fe2O3) = m(Fe2O3)/M(Fe2O3)

we know that n ~ 8944.54, and M = 2 x 55.9 + 3 x 16 = 159.8

therefore, if n = m/M then m = n x M = 8944.54 * 159.8 ~ 1429338g =1429.338kg

However, you're given FOUR sig figs in the question stem (1000 kg) so you give the answer as 1429kg.

bucket:
i keep getting 714kg as my answer, which is approximately half and i dont see where it would double in my method of working.
This is what I did.

m(fe) in the end is 1000kg.
i go m/M = 1000/112 = 8.93mol

the ratio is 1:2 (Fe2O3:2Fe)
so i halve the mol
8.93/2 = 4.46mol

now converting it back to mass
m(Fe2O3) = n X m = 4.46 x 160 = 713.6 or 714. around about half the answer.


sorry if its hard to understand my explanation
i havent looked at using latex yet.

bucket:
oh god thanks lol.
that other guy deleted his post, he was wrong anyway :P
cheers

enwiabe:
The book is wrong because it rounded off too early in the question. ALWAYS store values on your calculator. It should be 1429kg not 1430kg.

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