[Catalist] One for the Chemists

[Andrew Bland]

Hi All, to clarify you are correct that redox titrations are not in the syllabus. I was using the titration not for redox calculations, but rather as a test of titration procedure, correct use of equipment, calculation of moles and concentrations etc.

Thanks,
Andrew




Andrew Bland
Teacher

T:  +61 8 9752 5252
F:  +61 8 9752 5299
E:  abl at gmas.wa.edu.au<mailto:abl at gmas.wa.edu.au>
W: www.gmas.wa.edu.au<http://www.gmas.wa.edu.au>
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From: Catalist [mailto:catalist-bounces at lists.stawa.net] On Behalf Of Ann Moseley
Sent: Friday, 4 March 2016 11:47 AM
To: catalist at lists.stawa.net
Subject: Re: [Catalist] One for the Chemists

I thought the same! I couldn't see redox titrations anywhere?!

On 4 March 2016 at 11:32, de la Haye, Maya <delahaye.maya at cathednet.wa.edu.au<mailto:delahaye.maya at cathednet.wa.edu.au>> wrote:
Correct me if I am wrong but I thought redox titrations were out of the new curriculum?
Maya

Sent from my iPhone

On 3 Mar 2016, at 4:31 PM, Andrew Bland <abl at gmas.wa.edu.au<mailto:abl at gmas.wa.edu.au>> wrote:
Hi all, please check if you agree with this model answer, from a validation after a redox titration, permanganate + hydrogen peroxide. Thanks, Andrew.






Q: If insufficient acid is added in step 9, some of the permanganate ions will react to form MnO2 instead of Mn2+. The equation for this reaction is:


                                            2 MnO4- + 3H2O2 + 2H+  --> 2MnO2 + 4H2O +3O2

The original equation is:
                            2MnO4- + 5H2O2 + 6H+ --> 5O2 + 2Mn2+ +8 H2O





a. How would this affect the volume of KMnO4 used to reach the end point? (Would it be more or less). Explain why.


A: In the original reaction, 2 mol of MnO4- will react with 5 mol of H2O2. In the new reaction, 2 mol of MnO4- will react with 3 mol of H2O2, meaning that more MnO4- would be required to react with the same amount of H2O2 to reach the end point.
The result would be that the concentration of H2O2 would be over estimated.



Andrew Bland

Teacher


T:  +61 8 9752 5252<tel:%2B61%208%209752%205252>

F:  +61 8 9752 5299<tel:%2B61%208%209752%205299>

E:  abl at gmas.wa.edu.au<mailto:abl at gmas.wa.edu.au>

W: www.gmas.wa.edu.au<http://www.gmas.wa.edu.au>

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Ann Moseley
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