[nexisrocks]

I'm trying to write a report, talking about the Nernst equation and how you can quantify an analyte by noting the charge passed as the analyte is reduced (and continuing on this vein, how E relates to analyte concentration).  The report is aimed at third year chemistry students who have only a passing acquaintance with electrochemistry.


Having just introduced the Nernst equation, I then go on to say:

Faraday’s constant is the electric charge per mole of electrons, and is calculated by taking into account Avogadro’s number and the charge associated with one electron.  That is,

F= N_Ae

where NA is Avogadro’s number (6.022x10²³ mol^-1), and e is the magnitude of charge associated with one electron (1.602x10^-19 C).  As Faraday’s constant considers the charge for only one electron, the Nernst equation must take into account the number of electrons exchanged in order to account for systems in which multiple electrons are exchanged.   For example:

Fe^{2 +} + 2e^- → Fe

Fe → Fe²⁺ + 2e^-

where Fe²⁺ is the oxidized species, which is reduced at the cathode, and Fe is the reduced species, which is oxidized at the anode.  In this reaction, n = 2, because two electrons are being added/removed to the analyte. 
   As was just noted, each electron contains a magnitude of charge equal to 1.602x10^-19 C; note that one coulomb equals one ampere per unit time, and thus coulombs are related to current.  When the oxidized species undergoes reduction, each electron passes this charge, and a current flows; the magnitude of the current is proportional to the number of electrons flowing, which is proportional to moles of analyte in solution.  Thus, the analyte concentration can be determined by measuring the current generated from a redox reaction in an electrochemical cell.

I'm not really sure how correct that is, or if it even makes a whole lot of sense... if anyone has some comments or suggestions, I'd love to hear them!

[Borek]

Apart from the strange mentioning of Nernst equation, when just balanced reaction equation should be taken into account, text looks perfectly OK to me. Perhaps they meant Faraday's law.

Basic idea is: count electrons to know how many ions reacted.

Counting electrons is impractical, but can be replaced by current integration.