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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Problem of the Week Archive => Topic started by: Borek on October 15, 2012, 06:23:29 AM

Title: Problem of the week - 15/10/2012
Post by: Borek on October 15, 2012, 06:23:29 AM
Following five reactions have one common reactant and one common product:

A + HCl :rarrow: F + CrCl3 + H + I :spinup:
B + HCl :rarrow: F + G + H + I :spinup:
C + HCl :rarrow: F + H + I :spinup:
D + HCl :rarrow: G + H + I :spinup:
E + HCl :rarrow: H + I :spinup:

Identify all substances, knowing that C contains 31.83% of metal by mass.
Title: Re: Problem of the week - 15/10/2012
Post by: Rutherford on October 16, 2012, 12:51:41 PM
Okay, I think it's time to write my attempt:
A=K2Cr2O7
B=KMnO4
C=KClO3
D=MnO2
E=HClO
F=KCl
G=MnCl2
H=H2O
I=Cl2
Title: Re: Problem of the week - 15/10/2012
Post by: Borek on October 18, 2012, 06:27:16 AM
There is an alternative answer to E.
Title: Re: Problem of the week - 15/10/2012
Post by: Schrödinger on October 18, 2012, 06:47:13 AM
H2O2? Oxidizing HCl to Cl2 and hence itself getting reduced to H2O?
Title: Re: Problem of the week - 15/10/2012
Post by: Borek on October 18, 2012, 06:54:50 AM
Even simpler than that. Reaction I am thinking about was part of an industrial process.
Title: Re: Problem of the week - 15/10/2012
Post by: Rutherford on October 18, 2012, 08:11:26 AM
E=O2?
Title: Re: Problem of the week - 15/10/2012
Post by: Borek on October 18, 2012, 08:15:47 AM
Exactly.

http://en.wikipedia.org/wiki/Deacon_process
Title: Re: Problem of the week - 15/10/2012
Post by: XGen on October 19, 2012, 04:55:16 PM
If it's not an inconvenience, could you explain your beginning approach when tackling this problem? I'm interested to hear about it :o
Title: Re: Problem of the week - 15/10/2012
Post by: Borek on October 20, 2012, 01:53:09 PM
Seeing how in all cases there is a HCl present and a gas is produced can you venture a guess what the gas can be?
Title: Re: Problem of the week - 15/10/2012
Post by: Rutherford on October 20, 2012, 02:20:06 PM
If it's not an inconvenience, could you explain your beginning approach when tackling this problem? I'm interested to hear about it :o
Here is the whole approach. First I saw what Borek said, then I started from the last equation and then I went to the first. A is obviously a dichromate and F is a chloride of the metal in the dichromate. C is a chlorate of the metal, and I need only to put in the 31.83%. From the beginning I was thinking about potassium as the metal and then the calculation showed that it is surely potassium (I was thinking about H as water, because it is a common product of redox reactions in acidic solutions and it is present in every reaction in the problem). The rest is easy then.