Electrodes pH meter

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

Glass electrode pH meter with calomel reference electrode and salt bridge. 

Potential measurements were made as before (1) with a variety of wide-pH-range glass electrodes. The cells were maintained at 25.0 ( 0.1) °C, and potential readings were recorded when fiiey became constant to 0.1 mV. Measurements were repeated at least fiiree times with different combinations of electrodes, pH meters, and electrolyte concentrations ranging from 0.0005 to O.OIM."... 

A method developed for halogenated solvents is applieable for determining flie pH of water extracts of solvents. The solvent sample is shaken with distilled or deionized water and flie pH is determined either by comparing color upon flie addition of Gramercy universal indicator or by using a glass electrode pH meter. 

Apparatus. In order to carry out the analyses outlined in detail below, it is necessary to have available a photoelectric colorimeter and a glass electrode pH meter and titration assembly. 

Reference electrode Saturated calomel electrode pH meter with mV display, accuracy 5 mV Aqua regia ... 

Measurements of pH values were made with a Beckman glass-electrode pH meter generously furnished by Professor A. O. Beckman of these Laboratories. As a standard 0.05 M potassium hydrogen phthalate solution, pH 3.97, was used. Corrections were applied in alkaline solutions for error due to sodium and potassium ions present as recommended by the manufacturer of the instrument. 

A representation of the two electrodes of a glass-electrode pH meter. The glass membrane is made of a special glass that has an effective permeability to hydrogen ions. The potential of this electrode is determined by the concentration of hydrogen ions in the medium surrounding the glass membrane. 

By choosing the right electrode, pH meter, and accessories, the analyst can build a dedicated system for his or her application. A system capable of giving accurate, repeatable results time after time is critical, especially for difficult high-viscosity solutions. Measuring parameters as diverse as pH, ISE, conductivity, redox, and dissolved oxygen, the electrochemical meters olfer great ffexibility to measure dilferent properties in polymeric solutions. 

Moore EW. Determination of pH by the glass electrode pH meter calibration for gastric analysis. Gastroenterology 54 501-501, 1968. 

Dilute 30 ml of analytical reagent quality glacial acetic acid to 1000 ml with distilled water. Add carefully to this a solution of 3-4 g of analytical reagent quality sodium hydroxide in about 20 ml of water until the pH of the buffer lies in the range of 4,1-4.2 as measured by a glass-electrode pH meter. Store the solution in a polyethylene bottle. The solution is stable for many months in the absence of evaporation. 

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