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### Topic: 2 Ultra hard questions left...  (Read 3977 times)

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#### HT

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##### 2 Ultra hard questions left...
« on: November 26, 2009, 01:40:39 AM »
Hey guys... First time posting, I'm a univ student too

Doing an assignment. 5 other people and me have tackled through 9 problems, and just have 2 left. We've spent so many hours over days doing this, and we're just stuck. I've got like 10 pages of rough notes for each question, I'm just looking for the answer showing work now

Here are the questions:

Absorbance spectrosopy can be used to monitor changes in redox equilibria.  The figure below
shows the spectral changes of the redox protein cytochrome c as it changes from it oxidized to its
reduced form.  The protein is adsorbed on a transparent electrode and the spectra are obtained at
different applied potentials (given in the figure).  The total amount of protein is completely
oxidized at +250 mV, and the total amount of protein is completely reduced at -250 mV.  A
mixture of the two forms (oxidized and reduced) exists at all of the other four potentials.

a)  Let x be the fraction of protein in the reduced form.  Then, x = 0 for the peak in spectrum (a)
and x = 1 for the peak in spectrum (f).  Find the fraction of protein in the reduced form for
each of the four middle curves.

b)  From the results in part (a), calculate log([ red]/[ox]), then, using the Nernst equation,
calculate n, the number of electrons involved in the reaction, and E0.

It's referring to Figure1 in this link: http://img109.imageshack.us/img109/6228/fig1.jpg

11. Considering the spectra below, calculate
a) the molar absorptivities of Co-EDTA and Ni-EDTA at their peak maxima;
b) the concentration in g/L-1 of Co and Ni in the mixture (Fig c). Note: b = 1 cm.

Here is the figure for this question: http://img691.imageshack.us/img691/4421/fig2x.jpg

Thanks to anyone that helps. Due in 2 days
« Last Edit: November 26, 2009, 03:02:21 AM by Borek »

#### JGK

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##### Re: 2 Ultra hard questions left...
« Reply #1 on: November 26, 2009, 11:17:50 AM »
rules is rules, you need to show your attempts first
Experience is something you don't get until just after you need it.

#### HT

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##### Re: 2 Ultra hard questions left...
« Reply #2 on: November 26, 2009, 03:11:10 PM »
Ok well I can describe my attempts for #10, I don't know much about 11...

I would scan what I did, but I'll try and describe the gist of it.

For #10, I plotted absorbance with the fraction. It pretty much looked like a plot of 2 points with the given values. I can't think of what else to do after that...I tried using Nerst equation/stuff outlined in the original question to solve for the fraction, but I'm just lost : \

Any help is appreciated!