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Winter 2013 Midterm #8B

Posted: Thu Feb 09, 2017 4:18 pm
by Helena Vervaet 1N
When I was solving for the concentration of Fe2+ ions, I used the Nernst Equation that included ln instead of log. For most of the other problems in that midterm, answers using either ln or log were both stated as acceptable, but for #8B (pg.135) it looks like only the log equation should have been used. Can someone explain to me when you should use equations with ln vs. log?

Re: Winter 2013 Midterm #8B

Posted: Thu Feb 09, 2017 4:32 pm
by Chem_Mod
It does not matter whether you use the equation using ln or log. However, the answers using the different equations will not be exactly the same because the log equation is less accurate due to the constant. The log version of the nernst equation presents (RT/F) as a constant, rather than having to plug in the corresponding values when calculating. However, note that the temperature used to calculate this constant is assumed to be 298 K (25 degrees Celsius).

Re: Winter 2013 Midterm #8B

Posted: Sat Feb 11, 2017 9:12 pm
by Melanie_Wong_1K
This question actually concerns both #8b and 7 of the 2013 Midterm.

When you're using the Nerst Equation, how do you find n? The moles aren't given in either of the problems but the answer to #7 says n=10 and for #8b n=2. They don't seem to relate to the amount of moles in the chemical equations either.