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It is the hydrated gel which makes the pH electrode an ion-selective electrode. H + does not cross through the glass membrane of the pH electrode, it is the Na + which crosses and leads to a change in free energy. When an ion diffuses from a region of activity to another region of activity, there is a free energy change and this is what the pH ...
A platinum wire electrode is immersed in a saturated aqueous solution of quinhydrone, in which there is the following equilibrium C 6 H 6 O 2 ⇌ C 6 H 4 O 2 + 2H + +2e −. The potential difference between the platinum electrode and a reference electrode is dependent on the activity, +, of hydrogen ions in the solution.
Beckman Model M pH Meter, 1937 [1] Beckman model 72 pH meter, 1960 781 pH/Ion Meter pH meter by Metrohm. A pH meter is a scientific instrument that measures the hydrogen-ion activity in water-based solutions, indicating its acidity or alkalinity expressed as pH. [2]
In aquatic environments, platinum is often used due to its high electron transfer kinetics, [5] although an electrode made from several metals can be used in order to enhance the electron transfer kinetics. [6] The most common potentiometric electrode is by far the glass-membrane electrode used in a pH meter.
Commercial reference electrodes consist of a glass or plastic tube electrode body. The electrode consists of a metallic silver wire (Ag (s)) coated with a thin layer of silver chloride (AgCl), either physically by dipping the wire in molten silver chloride, chemically by electroplating the wire in concentrated hydrochloric acid (HCl) [3] or electrochemically by oxidising the silver at an anode ...
The most common types of reference electrodes used in analytical chemistry include the standard hydrogen electrode, the saturated calomel electrode, and the Ag/AgCl electrode. [ 3 ] The standard hydrogen electrode (SHE) is the primary reference electrode that has a potential of 0 volts at all temperatures and a pressure of 1 atm.