# Chemical Forums

## Chemistry Forums for Students => High School Chemistry Forum => Chemistry Olympiad and other competitions => Topic started by: Evaldas on December 30, 2010, 01:30:52 PM

Post by: Evaldas 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)  :rarrow: 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?
Title: Re: Olympiad question #2 (Salts)
Post by: Borek on December 30, 2010, 02:58:31 PM
How does mass of the plate change when 1 mol of iron reacts?
Title: Re: Olympiad question #2 (Salts)
Post by: Evaldas 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?
Title: Re: Olympiad question #2 (Salts)
Post by: Borek on December 30, 2010, 07:00:21 PM
Mass of the plate gets replaced with 1 mole of copper?

Title: Re: Olympiad question #2 (Salts)
Post by: Evaldas on December 31, 2010, 04:26:17 AM
Gets heavier because copper is heavier than iron?
Title: Re: Olympiad question #2 (Salts)
Post by: Borek on December 31, 2010, 06:08:40 AM
By how much?
Title: Re: Olympiad question #2 (Salts)
Post by: Evaldas 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?
Title: Re: Olympiad question #2 (Salts)
Post by: SchrÃ¶dinger on December 31, 2010, 06:46:14 AM
Yes. Correct :)
Title: Re: Olympiad question #2 (Salts)
Post by: Evaldas 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  :rarrow: 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.