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Other Electrochemical MethodsOther Electrochemical Methods

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Electrogravimetric AnalysisElectrogravimetric Analysis

• If you wanted to test for copper ions in solution (or some other ion), you could make an electrolysis cell.

• You would then run a current through the electrolytic cell containing the copper ions.

• This would force the copper ions to “plate” onto the cathode electrode.

• The change in mass of the cathode will tell you the original amount of copper ions in solution.

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Electrogravimetric AnalysisElectrogravimetric Analysis

• You do have to have a method to determine whether the reaction is complete.

• Sln color change• Fresh cathode has no more copper deposited.• Small aliquot of the sln tests negative for copper.

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Coulometric AnalysisCoulometric Analysis

• In coulometry, a current is run through a solution until a redox rxn is complete.

• This is measured with an indicator.• The time it took to complete the reaction is then

used to calculate the moles of electrons consumed.• This is then used to calculate the mass of the

original analyte.• Problem: If a current of 56.0 mA for 705 s was

required to reach the endpoint for the titration of 10.00 mL of a monoprotic acid, what was the molarity of the HA?

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AmperometryAmperometry

• In amperometry, the current between 2 electrodes driving an electrolysis reaction is measured.

• The voltage is fixed.• The measured current is proportional to the

amount of analyte.• Amperometry is used in oxygen monitors, glucose

monitors, and other sugars.• A calibration curve of known standards is used to

calculate the amount of an analyte.

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VoltammetryVoltammetry

• Now the current between 2 electrodes is measured while the voltage is changed.

• The method of standard addition is used so that a series of graphs is obtained.

• The concentration of the analyte is proportional to the peak current obtained from the graph.

• This was often used to measure Vitamin C.

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PolarographyPolarography

• This is a type of voltammetry.• One of the electrodes is a dropping-mercury

electrode.• It has the advantage that mercury is less likely to

reduce H+ to hydrogen gas.• Otherwise, the process is similar.