Measuring galvanic-cell potential {potentiometry} can find ion concentration.
purposes
Potentiometry measures body-fluid, column-effluent, waste-water, pool, detergent, silver-thiocyanate solution, iodide, bromide, chloride, calcium, nitrate, copper, lead, sulfate, aluminum, phosphate, metal-plating cyanide wastes, bleach-chlorine, paper-bleach, water-pollution, and sewage ions. Titration by potentiometer is accurate.
Potentiometry is for redox reactions, precipitations, acid-base reactions, complexing, or indicators. pH meters and ion detectors use direct potentiometry or potential change followed by titration.
potentiometer
Potentiometers measure voltage at zero current, to eliminate internal resistance. Potentiometer has reference electrode and indicator electrode. Circuit has equal and opposite voltage.
Exact-voltage cells {Weston cell} can calibrate potentiometers.
At halfway to equilibrium, potential equals sample potential. At equivalence, potential is half sum of sample potential and titration ions, if valences are equal. Otherwise, it is weighted average. On graph, steepest slope is equivalence point.
potentiometer: reference electrode
Reference electrodes can change voltage by salt-bridge ion-flow-rate change, temperature change, pH change, electrical-resistance change, and mercury, potassium, or chloride sample contamination.
potentiometer: indicator electrode
Indicator electrodes are for redox reactions. Indicator electrodes must be rapid and exact. If both molecules are ions, electrodes are platinum. If ions are strong reducing agents, electrodes are gold. Strong reducing agents are chromium, titanium, or vanadium. If system uses metal and ion, and metal does not react in water, electrodes are gold. Silver, cadmium, mercury, and copper do not react in water. If system uses metal and low-solubility salt, electrodes are gold. Hydrogen electrode is for pH.
Physical Sciences>Chemistry>Analytical Chemistry>Electricity
5-Chemistry-Analytical Chemistry-Electricity
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Date Modified: 2022.0224