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#Post#: 1942--------------------------------------------------
Problem of the week-14/01/2012
DIR By: Michel
Date: January 15, 2013, 9:59 am
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Here's the first POTW of the year!
Electrolysis of NaCl solution using a metal electrode produced a
precipitate X during the course of the electrolysis. the
precipitate was collected, washed and dried.
A moderately concentrated solution of an unknown alkali Y was
added to an isolated mass of precipitate X. the precipitate
dissolved forming a colorless solution.
A few grams of the ppt was heated in air and it changed from
its original color to black. the black powder was collected and
labelled Z. Adding Z to the unknown alkali produces no visible
reaction. exposing the solution of X in the unknown alkali
rapidly changes the color from colorless to blue.
I've hidden quite some detail here...but some clues lie here
and there as usual.
Identify all the unknown compounds and suggest one way to
selectively precipitate the chloride of the metal in the
electrolysis (instead of precipitating X)
#Post#: 1986--------------------------------------------------
Re: Problem of the week-14/01/2012
DIR By: Michel
Date: January 24, 2013, 8:49 am
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Okay guys...i'm back here now, so you can start posting your
attempts. thank you
#Post#: 2019--------------------------------------------------
Re: Problem of the week-14/01/2012
DIR By: Michel
Date: January 30, 2013, 9:54 pm
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any takers? come on!
#Post#: 2020--------------------------------------------------
Re: Problem of the week-14/01/2012
DIR By: Chemist@
Date: January 31, 2013, 11:09 am
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Let's say:
X=Cu(OH)2
Y=NaOH
Z=CuO
Reaction: Cu(OH)2+2NaOH→Na2[Cu(OH)4]
Selective precipitation, maybe in acidic environment and
crystallization afterwards.
#Post#: 2047--------------------------------------------------
Re: Problem of the week-14/01/2012
DIR By: Michel
Date: February 7, 2013, 7:22 am
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not exactly what I had in mind, but X is a compound of copper.
recall that Y is a weak alkali...so its definitely not NaOH. Try
another?
the black powder is CuO. Really, I did not know that it is
possible for Cu(OH)2 to complex with NaOH? It gives a strong
case for Cu(OH)2. So what do you think I had in mind about X
::).....heheha try a guess? X will form a colorless solution
with the weak alkali. then what could be the color of X?
I'M REALLY SORRY FOR MY LATE REPLY...I'VE BEEN VERY BUSY AND NOT
HAD AS MUCH TIME AS I NORMALLY DO ON THIS FORUM.
Hopefully, when I tidy things up this week, I could be more
active here.
#Post#: 2048--------------------------------------------------
Re: Problem of the week-14/01/2012
DIR By: Chemist@
Date: February 7, 2013, 12:37 pm
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Then the base is ammonia. Not sure for X.
#Post#: 2050--------------------------------------------------
Re: Problem of the week-14/01/2012
DIR By: Michel
Date: February 7, 2013, 7:36 pm
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Yeah...the base is certainly NH3. Hint. X as a compound of Cu is
quite common...
#Post#: 2058--------------------------------------------------
Re: Problem of the week-14/01/2012
DIR By: Chemist@
Date: February 8, 2013, 12:27 pm
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If colorless the probably a Cu+ compound, maybe CuCl?
#Post#: 2060--------------------------------------------------
Re: Problem of the week-14/01/2012
DIR By: Michel
Date: February 9, 2013, 12:42 am
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CuCl?..no, but close. Probably searching the inorganic section
of this forum will show you the answer...d'you mind trying that?
#Post#: 2061--------------------------------------------------
Re: Problem of the week-14/01/2012
DIR By: Michel
Date: February 9, 2013, 12:43 am
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CuCl?..no, but close. Probably searching the inorganic section
of this forum will show you the answer...d'you mind trying that?
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