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Evaldas

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« on: December 30, 2010, 01:30:52 PM »
10 g iron plate was submerged into 200 g 8% copper(II) sulfate solution. After some time the plate was taken out and it got heavier by 0,8 g. Find out:
a) did all the copper(II) sulfate react?
Reaction:
CuSO4(aq) + Fe(s)   FeSO4(aq) + Cu(s)
m(CuSO4) = 16 g.
What's next?
n(Fe)=0.17857 mol; n(CuSO4)=0.1 mol?
All the copper sulfate reacted because there was excess of iron?

Borek

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« Reply #1 on: December 30, 2010, 02:58:31 PM »
How does mass of the plate change when 1 mol of iron reacts?
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Evaldas

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« Reply #2 on: December 30, 2010, 03:08:19 PM »
How does mass of the plate change when 1 mol of iron reacts?
Gets replaced with 1 mol of copper?

Borek

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« Reply #3 on: December 30, 2010, 07:00:21 PM »
Mass of the plate gets replaced with 1 mole of copper?

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Evaldas

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« Reply #4 on: December 31, 2010, 04:26:17 AM »
Gets heavier because copper is heavier than iron?

Borek

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« Reply #5 on: December 31, 2010, 06:08:40 AM »
By how much?
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Evaldas

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« Reply #6 on: December 31, 2010, 06:25:40 AM »
If we're speaking about 1 mol of each then the difference between M(Fe) and M(Cu), 64g/mol-56g/mol=8g/mol.
Right?

SchrÃ¶dinger

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« Reply #7 on: December 31, 2010, 06:46:14 AM »
Yes. Correct
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Evaldas

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« Reply #8 on: December 31, 2010, 07:36:53 AM »
This is what solution they suggest (saying that it is one of the many possible):
CuSO4 + Fe  FeSO4 + Cu
Reacted:    x mol    x mol
Formed:                          x mol   x mol
Reacted iron mass: 56x, formed copper mass 64x
:delta: m = -56x + 64x = +0,80
from here x = 0,1 mol. That means 0,1 mol of CuSO4 reacted (which is 16 g) and 0,1 mol of FeSO4 formed (which is 15,2 g)
There were 16 g of CuSO4 in the solution so it means all the CuSO4 reacted.

Do you think this exercise is too easy/difficult for students who are in the last two years of high school chemistry?

Borek

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« Reply #9 on: December 31, 2010, 11:41:23 AM »
You have checked that 8g mass difference means 1 mole reacted, next step is to answer the question - if 8g change in mass means 1 mole reacted, how many moles reacted if mass changed by 0.8g?

That's the same approach they used, they too combined mass difference with number of moles.
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Evaldas

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