Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: busi6292 on July 30, 2009, 12:40:07 PM
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Hello all again,
A mixture os 8g iron and 4g sulphur is heated and the elements react to form iron II sulphide/ How much iron will be left over at the end of the reaction.
I calculated the moles for each symbol and did 0.14 X 88 = 12.57 for iron and 0.125 X 88 = 11 for sulphur therefore the answer is 1.57g, am I right?
Thanks again.
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Hello all again,
A mixture os 8g iron and 4g sulphur is heated and the elements react to form iron II sulphide/ How much iron will be left over at the end of the reaction.
I calculated the moles for each symbol and did 0.14 X 88 = 12.57 for iron and 0.125 X 88 = 11 for sulphur therefore the answer is 1.57g, am I right?
Thanks again.
I'm not quite sure where your "0.14 x 88" or "0.125 x 88" come from, can you post again, with units, perhaps?
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Hello here is what I have..this is so confusing because each question is worded slightly different.
Fe + S -------> Fe S
RAM 56 32 56 + 32 = 88
MOLES 8/56 4/32 8 and 4 being the mass given in the Q
ANSWER 0.14 0.125
Don't really know from here so I thought
0.14 X 88 (the RAM At other sider) = 12.57g for Fe
0.125 X 88 = 11g
Difference is 1.57g as it asks how much is left over?
Thanks!
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Hello here is what I have..this is so confusing because each question is worded slightly different.
Fe + S -------> Fe S
RAM 56 g/mol 32 g/mol 56 + 32 = 88 g/mol
MOLES 8 g/56 g/mol 4/32 8 and 4 being the mass given in the Q
ANSWER 0.14 mol 0.125 mol (SJB)
Everything seems fine until here, so...
You have 0.14 mol of iron and 0.125 mol of sulfur. Which reagent is in excess, according to your reaction equation?
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The iron is in excess.
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OK, so (based on our other conversation I'll perhaps harry things along a bit)
How many moles of iron are you in excess by?
What is the mass of this amount of iron?
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Well 0.14/0.125 = 1.12 so 0.12 moles in excess.
0.14 - 0.125 = 0.015 in excess.
Was that right to your qs?
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First answer - not quite. If I had 2 apples and 3 oranges, and you took away apples and oranges in equal numbers until I had no more of one or other fruit, would I really have 0.5 (3/2 - 1) oranges left?
Instead, as you have realised in the second sentence, I'd have 3-2 = 1 orange left, so in the actual question you'd have 0.015 mol of iron in excess.
So, what is the mass of 0.015 mol of iron?
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Okay so mass = moles X ram
0.015 x 56 = 0.84g.
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Sounds fine to me. I'd perhaps not round off the number of moles of iron that there were initially so early - I can see why you've done it (2 sf and all that), but in that case why did you not round off the moles of sulfur, too?
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Brilliant thanks!
Probably because doing the method was done in a duration of 5 days!
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Probably because doing the method was done in a duration of 5 days!
Well, such is the nature of collaboration. Don't forget, there is more than just your town, or even timezone on the internet. I'm sure if we had been sitting next to one another in the library or similar then it would have been over within an hour or so.
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Yes I know but I was just telling you why I didn't round the moles to the same significant figures as other calculations.