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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]
The bottom of a pH electrode balloons out into a round thin glass bulb. The pH electrode is best thought of as a tube within a tube. The inner tube contains an unchanging 1×10 −7 mol/L HCl solution. Also inside the inner tube is the cathode terminus of the reference probe.
The most common potentiometric electrode is by far the glass-membrane electrode used in a pH meter. A variant of potentiometry is chronopotentiometry which consists in using a constant current and measurement of potential as a function of time. It has been initiated by Weber. [7]
Primary pH standard values are determined using a concentration cell with transference by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode. The pH of aqueous solutions can be measured with a glass electrode and a pH meter or a color-changing indicator.
In and of themselves, pH indicators are usually weak acids or weak bases. The general reaction scheme of acidic pH indicators in aqueous solutions can be formulated as: HInd (aq) + H 2 O (l) ⇌ H 3 O + (aq) + Ind − (aq) where, "HInd" is the acidic form and "Ind −" is the conjugate base of the indicator. Vice versa for basic pH indicators ...
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 ...
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The antimony electrode has been investigated for its ability to function as a pH electrode. [1] The electrode is made of elemental antimony. The electrochemical process can be formulated as Sb 2 O 3 (s) + 6 H + + 6 e − ⇌ 2Sb(s) + 3H 2 O. The oxide, Sb 2 O 3, is present on the surface of the electrode. Although this electrode does not give ...