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Homework Help: Electrolysis, factors=>n(product)

  1. Apr 25, 2008 #1
    [SOLVED] Electrolysis, factors=>n(product)

    2. Relevant equation
    Which pair of factors both affect the amount (in mol) of chlorine produced in the electrolysis of aqueous
    sodium chloride?
    A. current and temperature
    B. temperature and chloride ion concentration
    C. chloride ion concentration and length of time of electrolysis
    D. pressure and length of time of electrolysis

    3. The attempt at a solution
    The right answer is C but why? I know that Current and time of electrolysis affects on the amount (as It=nzF). However, I do not why Temperature or pressure do not affect on the amount and why [Cl] does. Please, say your comment on this question.
  2. jcsd
  3. Apr 25, 2008 #2
    in a dilute aqueous solution of NaCl, H+ and OH- are preferentially discharged. there would not be any Cl- discharged. but, you have a concentrated solution of NaCl (brine), the discharge of Cl- becomes energetically feasible over the discharge of H+ (which is also discharged to a certain extent). the temperature has no effect on the production of Cl2, neither does pressure. temperature or pressure might affect the amount of Cl2 collected because Cl2 is very soluble in water, but they will not affect the yield of Cl2.
  4. Apr 26, 2008 #3
    The question is about the amount. So your point is that [Cl-] plays a more important role in determining the amount of Cl2 formed and the effects of temperature and pressure are insignificant compareted to that of [Cl-].
  5. Apr 26, 2008 #4
    yeah, the preferential discharge of Cl- (instead of the OH- which although has a higher electrode potential) is independent of changes in temperature or pressure.
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