DIR Return Create A Forum - Home
---------------------------------------------------------
Chemistry:The Central Science
HTML https://kolathechemist.createaforum.com
---------------------------------------------------------
*****************************************************
DIR Return to: General chemistry discussion
*****************************************************
#Post#: 1012--------------------------------------------------
Problem of the week-29/10/12
DIR By: Michel
Date: October 28, 2012, 6:05 pm
---------------------------------------------------------
Here's one for open discussion and analysis ;)
During the electrolysis of a solution containing 2.5 M NaCl and
2M Al2(SO4)3 using a copper anode and an Iron cathode, and a 9V
battery, it is found that one electrode reduces in mass slowly,
while the mass change in the other electrode isn't much. The
cell was run for 6 hours and during this period the electrolyte
assumed two different colors, apart from the initial colorless
solution. Briefly explain the chemistry of the electrolysis;
including which electrode significantly reduced in mass, and the
two different colors you expect the electrolyte to have during
the course of the electrolysis.
#Post#: 1025--------------------------------------------------
Re: Problem of the week-29/10/12
DIR By: Michel
Date: October 31, 2012, 12:32 am
---------------------------------------------------------
No takers? I assumed we'd love a break from calculating molar
masses and finding unknown compounds :|
#Post#: 1032--------------------------------------------------
Re: Problem of the week-29/10/12
DIR By: Chris
Date: November 1, 2012, 9:02 am
---------------------------------------------------------
no idea...:O
#Post#: 1039--------------------------------------------------
Re: Problem of the week-29/10/12
DIR By: Michel
Date: November 2, 2012, 9:25 am
---------------------------------------------------------
--- Quote from: Chris link ---
>
> no idea...:O
>
--- End Quote ---
really the problem is simple and almost straightforward; Come
on! You should have some ideas! and you can say your Ideas...
#Post#: 1049--------------------------------------------------
Re: Problem of the week-29/10/12
DIR By: Michel
Date: November 5, 2012, 4:06 pm
---------------------------------------------------------
Well...so far no takers :( I'm extending it for this week. At
least share your thoughts and opinions
#Post#: 1059--------------------------------------------------
Re: Problem of the week-29/10/12
DIR By: LikeCrazy
Date: November 6, 2012, 9:06 pm
---------------------------------------------------------
Is it possible for the Al2(SO4)3 to react with the NaCl...
#Post#: 1062--------------------------------------------------
Re: Problem of the week-29/10/12
DIR By: Michel
Date: November 6, 2012, 9:48 pm
---------------------------------------------------------
No. You won't have any reaction between the ionic species in
solution before the passahe of the direct current through the
solution. During the electrolysis, redox reactions will occur,
not necessarily reaction between NaCl and aluminium sulfate
#Post#: 1090--------------------------------------------------
Re: Problem of the week-29/10/12
DIR By: Michel
Date: November 10, 2012, 8:38 am
---------------------------------------------------------
hmmn...I just realised we're in the end of another week. Surely
this question is boring? or difficult? or do you think it's
plainly wrong?
I do not like posting a new POTW when the old one remains
unsolved, but I'm tempted to...
#Post#: 1107--------------------------------------------------
Re: Problem of the week-29/10/12
DIR By: Potla
Date: November 11, 2012, 8:39 pm
---------------------------------------------------------
I might give it a shot...
The solution contains the following cations and anions:
Na+, Al3+, H+;
SO42-, OH-, Cl-.
We are using Cu anode and Fe cathode. So H+ gets oxidised to H2,
and bubbles out of the solution. As Fe is more reactive than Cu,
it comes to the solution, initially as Fe2+ and later as Fe3+.
So the mass of the Cu electrode does not change much, the Fe
electrode gets smaller in mass, and the colour of the solution
changes from green to yellow.
Hope that's correct. :)
#Post#: 1110--------------------------------------------------
Re: Problem of the week-29/10/12
DIR By: Michel
Date: November 12, 2012, 2:07 am
---------------------------------------------------------
--- Quote from: Potla link ---
>
> I might give it a shot...
>
> The solution contains the following cations and anions:
> Na+, Al3+, H+;
> SO42-, OH-, Cl-.
>
> We are using Cu anode and Fe cathode. So H+ gets oxidised to
H2, and bubbles out of the solution. As Fe is more reactive than
Cu, it comes to the solution, initially as Fe2+ and later as
Fe3+. So the mass of the Cu electrode does not change much, the
Fe electrode gets smaller in mass, and the colour of the
solution changes from green to yellow.
>
> Hope that's correct. :)
>
--- End Quote ---
Not exactly what I expected...you got the color changes quite
allright, but you didn't get which electrode reduces in mass,
and why.. Remember, it's NaCl/Al2(SO4)3. The solution isn't
acidic enough to dissolve Fe. Now you know it's the anode that
reduces in mass. Can you explain why?
*****************************************************
Page 1 of 2
DIR Next Page