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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

Quote from: 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

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.