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Chapter 24 Coulometry 1 Principles of electrolysis
Current-voltage relationship 1.1 Electrolysis at constant potential
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Fig. 24-1c (p.698) Change in (a) current and (b) potential during deposition of Cu2+.
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Eappl E – Eref = constant Fig (p.701) Apparatus for controlled-potential electrolysis.
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2 Coulometric methods Faraday’s Law (relating the number of moles of the analyte nA to the charge
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2.1 Controlled-potential coulometry
Can also be used for determination of organic compounds (if they can be reduced at mercury cathode whose potential is suitably controlled)
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Fig. 24-6 (p.705) Schematic of a system for controlled-potential coulometry
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2.2 Coulometric titration – controlled current coulometry
Notes: 1. current efficiency = 100% 2. need a end-point detection (color changes, potentiometric, photometric measurement) Karl Fisher determination of water 2I- I2 + 2e- I2 + SO2 + 2H2O 2 HI + H2SO4 2HI + H2O + SO2 + 3C5H5N 2(C5H5N+H)I- + C5H5N.SO3 C5H5N.SO3 + CH3OH (C5H5N+H)O.SO2.OCH3
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Fig. 24-8 (p.708) An automated coulometric titrator.
Fig (p.709) A typical coulometric titration cell
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