what ion is a ph electrode selectively sensitive to? give its formula.

Instrument that indicates acidity or alkalinity in water-based solutions, expressed every bit pH

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 activeness in water-based solutions, indicating its acidity or alkalinity expressed as pH.^[2] The pH meter measures the difference in electric potential between a pH electrode and a reference electrode, and and then the pH meter is sometimes referred to as a "potentiometric pH meter". The difference in electrical potential relates to the acidity or pH of the solution.^[3] The pH meter is used in many applications ranging from laboratory experimentation to quality command.^[4]

Applications [edit]

The charge per unit and outcome of chemical reactions taking place in water ofttimes depends on the acidity of the water, and it is therefore useful to know the acidity of the water, typically measured past ways of a pH meter.^[5] Knowledge of pH is useful or critical in many situations, including chemical laboratory analyses. pH meters are used for soil measurements in agriculture, water quality for municipal water supplies, swimming pools, environmental remediation; brewing of wine or beer; manufacturing, healthcare and clinical applications such as claret chemical science; and many other applications.^[4]

Advances in the instrumentation and in detection accept expanded the number of applications in which pH measurements tin can be conducted. The devices have been miniaturized, enabling straight measurement of pH inside of living cells.^[6] In addition to measuring the pH of liquids, specially designed electrodes are available to measure the pH of semi-solid substances, such as foods. These have tips suitable for piercing semi-solids, have electrode materials compatible with ingredients in food, and are resistant to clogging.^[7]

Design and use [edit]

Using an early Beckman pH meter in a lab

Principle of functioning [edit]

Potentiometric pH meters measure the voltage between two electrodes and display the result converted into the corresponding pH value. They incorporate a simple electronic amplifier and a pair of electrodes, or alternatively a combination electrode, and some grade of display calibrated in pH units. It usually has a glass electrode and a reference electrode, or a combination electrode. The electrodes, or probes, are inserted into the solution to be tested.^[8]

The pattern of the electrodes is the central part: These are rod-similar structures normally made of drinking glass, with a seedling containing the sensor at the lesser. The glass electrode for measuring the pH has a glass bulb specifically designed to be selective to hydrogen-ion concentration. On immersion in the solution to exist tested, hydrogen ions in the test solution substitution for other positively charged ions on the glass bulb, creating an electrochemical potential across the bulb. The electronic amplifier detects the departure in electrical potential betwixt the two electrodes generated in the measurement and converts the potential deviation to pH units. The magnitude of the electrochemical potential across the glass bulb is linearly related to the pH according to the Nernst equation.

The reference electrode is insensitive to the pH of the solution, being composed of a metallic conductor, which connects to the display. This conductor is immersed in an electrolyte solution, typically potassium chloride, which comes into contact with the test solution through a porous ceramic membrane.^[9] The brandish consists of a voltmeter, which displays voltage in units of pH.^[9]

On immersion of the glass electrode and the reference electrode in the exam solution, an electric excursion is completed, in which there is a potential difference created and detected past the voltmeter. The circuit can exist thought of as going from the conductive element of the reference electrode to the surrounding potassium-chloride solution, through the ceramic membrane to the test solution, the hydrogen-ion-selective glass of the drinking glass electrode, to the solution inside the glass electrode, to the silver of the glass electrode, and finally the voltmeter of the display device.^[ix] The voltage varies from test solution to test solution depending on the potential difference created by the divergence in hydrogen-ion concentrations on each side of the glass membrane between the exam solution and the solution inside the glass electrode. All other potential differences in the circuit do not vary with pH and are corrected for past means of the calibration.^[9]

For simplicity, many pH meters employ a combination probe, synthetic with the glass electrode and the reference electrode independent within a single probe. A detailed clarification of combination electrodes is given in the article on drinking glass electrodes.^[10]

The pH meter is calibrated with solutions of known pH, typically earlier each use, to ensure accuracy of measurement.^[11] To mensurate the pH of a solution, the electrodes are used as probes, which are dipped into the exam solutions and held there sufficiently long for the hydrogen ions in the test solution to equilibrate with the ions on the surface of the bulb on the glass electrode. This equilibration provides a stable pH measurement.^[12]

pH electrode and reference electrode design [edit]

Details of the fabrication and resulting microstructure of the drinking glass membrane of the pH electrode are maintained every bit trade secrets past the manufacturers.^{[13] : 125} Notwithstanding, certain aspects of design are published. Glass is a solid electrolyte, for which alkali-metallic ions tin can behave current. The pH-sensitive glass membrane is more often than not spherical to simplify the manufacture of a uniform membrane. These membranes are up to 0.iv millimeters in thickness, thicker than original designs, then equally to render the probes durable. The glass has silicate chemical functionality on its surface, which provides binding sites for alkali-metallic ions and hydrogen ions from the solutions. This provides an ion-exchange capacity in the range of ten^{−half-dozen} to x^−eight mol/cm^two. Selectivity for hydrogen ions (H⁺) arises from a balance of ionic charge, book requirements versus other ions, and the coordination number of other ions. Electrode manufacturers have developed compositions that suitably balance these factors, well-nigh notably lithium glass.^{[13] : 113–139}

The silver chloride electrode is most unremarkably used every bit a reference electrode in pH meters, although some designs utilise the saturated calomel electrode. The silver chloride electrode is simple to manufacture and provides loftier reproducibility. The reference electrode normally consists of a platinum wire that has contact with a silver/silver chloride mixture, which is immersed in a potassium chloride solution. There is a ceramic plug, which serves equally a contact to the test solution, providing low resistance while preventing mixing of the two solutions.^{[thirteen] : 76–91}

With these electrode designs, the voltmeter is detecting potential differences of ±1400 millivolts.^[14] The electrodes are farther designed to speedily equilibrate with test solutions to facilitate ease of employ. The equilibration times are typically less than one second, although equilibration times increment as the electrodes age.^{[13] : 164}

Maintenance [edit]

Because of the sensitivity of the electrodes to contaminants, cleanliness of the probes is essential for accuracy and precision. Probes are generally kept moist when non in use with a medium advisable for the particular probe, which is typically an aqueous solution available from probe manufacturers.^{[11] [15]} Probe manufacturers provide instructions for cleaning and maintaining their probe designs.^[11] For illustration, ane maker of laboratory-grade pH gives cleaning instructions for specific contaminants: general cleaning (15-minute soak in a solution of bleach and detergent), table salt (hydrochloric acid solution followed by sodium hydroxide and water), grease (detergent or methanol), clogged reference junction (KCl solution), protein deposits (pepsin and HCl, 1% solution), and air bubbles.^{[15] [16]}

Calibration and operation [edit]

5.739 pH/Ion at 23 °C temperature shown on photo. pH 7110 pH meter manufactured by inoLab

The German Constitute for Standardization publishes a standard for pH measurement using pH meters, DIN 19263.^[17]

Very precise measurements necessitate that the pH meter is calibrated before each measurement. More typically calibration is performed one time per day of performance. Calibration is needed because the drinking glass electrode does not give reproducible electrostatic potentials over longer periods of fourth dimension.^{[xiii] : 238–239}

Consistent with principles of skilful laboratory exercise, calibration is performed with at least two standard buffer solutions that span the range of pH values to be measured. For general purposes, buffers at pH iv.00 and pH 10.00 are suitable. The pH meter has 1 calibration command to ready the meter reading equal to the value of the first standard buffer and a 2d command to arrange the meter reading to the value of the second buffer. A third control allows the temperature to exist set up. Standard buffer sachets, available from a variety of suppliers, usually document the temperature dependence of the buffer control. More precise measurements sometimes require calibration at three different pH values. Some pH meters provide built-in temperature-coefficient correction, with temperature thermocouples in the electrode probes. The calibration procedure correlates the voltage produced past the probe (approximately 0.06 volts per pH unit) with the pH scale. Expert laboratory practice dictates that, later each measurement, the probes are rinsed with distilled water or deionized water to remove any traces of the solution being measured, blotted with a scientific wipe to absorb any remaining water, which could dilute the sample and thus alter the reading, and and then immersed in a storage solution suitable for the item probe type.^[18]

Types of pH meters [edit]

In full general there are three major categories of pH meters. Benchtop pH meters are often used in laboratories and are used to measure samples which are brought to the pH meter for analysis. Portable, or field pH meters, are handheld pH meters that are used to have the pH of a sample in a field or product site.^[nineteen] In-line or in situ pH meters, as well called pH analyzers, are used to measure out pH continuously in a process, and can stand up-lone, or exist connected to a higher level information system for process control.^[20]

pH meters range from simple and inexpensive pen-similar devices to complex and expensive laboratory instruments with computer interfaces and several inputs for indicator and temperature measurements to exist entered to suit for the variation in pH caused by temperature. The output can be digital or analog, and the devices can be battery-powered or rely on line power. Some versions employ telemetry to connect the electrodes to the voltmeter display device.^{[13] : 197–215}

Specialty meters and probes are available for use in special applications, such as harsh environments^[21] and biological microenvironments.^[six] There are too holographic pH sensors, which let pH measurement colorimetrically, making use of the multifariousness of pH indicators that are available.^[22] Additionally, at that place are commercially bachelor pH meters based on solid state electrodes, rather than conventional glass electrodes.^[23]

History [edit]

"Here'southward the new Beckman Pocket pH Meter", 1956

The concept of pH was defined in 1909 by S. P. 50. Sørensen, and electrodes were used for pH measurement in the 1920s.^[24]

In October 1934, Arnold Orville Beckman registered the first patent for a consummate chemical instrument for the measurement of pH, U.S. Patent No. 2,058,761, for his "acidimeter", later on renamed the pH meter. Beckman developed the prototype as an assistant professor of chemical science at the California Institute of Technology, when asked to devise a quick and accurate method for measuring the acidity of lemon juice for the California Fruit Growers Exchange (Sunkist).^{[25] : 131–135}

On April eight, 1935, Beckman's renamed National Technical Laboratories focused on the manufacture of scientific instruments, with the Arthur H. Thomas Company as a benefactor for its pH meter.^{[25] : 131–135} In its first full year of sales, 1936, the company sold 444 pH meters for $sixty,000 in sales.^[26] In years to come, the visitor sold millions of the units.^{[27] [28]} In 2004 the Beckman pH meter was designated an ACS National Historic Chemic Landmark in recognition of its significance as the first commercially successful electronic pH meter.^[26]

The Radiometer Corporation of Denmark was founded in 1935, and began marketing a pH meter for medical use around 1936, but "the evolution of automatic pH-meters for industrial purposes was neglected. Instead American musical instrument makers successfully adult industrial pH-meters with a wide variety of applications, such as in breweries, paper works, alum works, and water handling systems."^[24]

In the 1940s the electrodes for pH meters were often difficult to make, or unreliable due to breakable drinking glass. Dr. Werner Ingold began to industrialize the production of unmarried-rod measuring cells, a combination of measurement and reference electrode in one construction unit,^[29] which led to broader acceptance in a broad range of industries including pharmaceutical production.^[xxx]

Beckman marketed a portable "Pocket pH Meter" as early on as 1956, but it did not have a digital read-out.^[31] In the 1970s Jenco Electronics of Taiwan designed and manufactured the first portable digital pH meter. This meter was sold under the label of the Cole-Parmer Corporation.^[32]

Building a pH meter [edit]

Specialized manufacturing is required for the electrodes, and details of their blueprint and construction are typically trade secrets.^{[13] : 125} Even so, with buy of suitable electrodes, a standard multimeter tin can be used to complete the construction of the pH meter.^[33] However, commercial suppliers offering voltmeter displays that simplify use, including calibration and temperature compensation.^[7]

See also [edit]

• Ion-selective electrodes
• ISFET pH electrode
• Potentiometry
• Quinhydrone electrode
• Saturated calomel electrode
• Silvery chloride electrode
• Standard hydrogen electrode

References [edit]

1. ^ "Beckman Coulter Production Milestones" (PDF). Beckman Coulter . Retrieved 5 April 2017.
2. ^ "pH meter". Encyclopædia Britannica Online. 2016. Retrieved 10 March 2016.
3. ^ Oxford Lexicon of Biochemistry and Molecular Biology (2 ed.), ed. Richard Cammack, Teresa Atwood, Peter Campbell, Howard Parish, Anthony Smith, Frank Vella, and John Stirling, Oxford Academy Press 2006, ISBN 9780198529170
4. ^ ^{a b} "pH Measurement and Value". Global Water. Xylem, Inc. Retrieved 21 March 2017.
5. ^ Bong, Ronald Percy. "Acid-Base of operations Reaction". Encyclopaedia Britannica. Encyclopaedia Britannica, Inc. Retrieved 21 March 2017.
6. ^ ^{a b} Loiselle, F.B.; Casey, J.R. (2010). Measurement of Intracellular pH. Methods in Molecular Biology. Vol. 637. pp. 311–31. doi:ten.1007/978-1-60761-700-6_17. ISBN978-1-60761-699-3. PMID 20419443.
7. ^ ^{a b} "pH Measurement Handbook" (PDF). PragoLab. Thermo Scientific, Inc. Retrieved 22 March 2017.
8. ^ Riddle, Peter (2013). "pH meters and their electrodes: scale, maintenance and use". The Biomedical Scientist. April: 202–205.
9. ^ ^{a b c d} Anthoni, J. Flooring. "pH Meter Principles". seafriends.org. Seafriends Marine Conservation and Education Middle. Retrieved 28 March 2017.
10. ^ Vanýsek, Petr (2004). "The Glass pH Electrode" (PDF). Interface. No. Summer. The Electrochemical Society. pp. xix–20. Retrieved three April 2017.
11. ^ ^{a b c} Bitesize Bio: How to Intendance for Your pH Meter, Steffi Magub, 18 May 2012.
12. ^ "Theory and Do of pH Measurement" (PDF). Emerson Procedure Direction. December 2010.
13. ^ ^{a b c d e f g} Galster, Helmuth (1991). pH Measurement: Fundamentals, Methods, Applications, Instrumentation. Weinheim: VCH Publishers, Inc. ISBN978-three-527-28237-1.
14. ^ Ltd, West Thou Pye and Co (1962). "Potentiometric pH Meter". Periodical of Scientific Instruments. 39 (half dozen): 323. doi:10.1088/0950-7671/39/6/442.
15. ^ ^{a b} MRC lab: How to Shop, Make clean, and Recondition pH Electrodes.
16. ^ Cleaning electrodes.
17. ^ "pH Measurement - pH Measuring Chains". Beuth publishing DIN. Beuth Verlag GmbH. Retrieved 28 March 2017.
18. ^ "How to perform a pH meter calibration". all-near-pH.com . Retrieved fourteen December 2016.
19. ^ "What is a pH Meter and How Does information technology Work?". Mettler-Toledo LLC. Retrieved 21 July 2021.
20. ^ "A guide to pH Measurement Theory and Exercise". Mettler-Toledo LLC. Retrieved 21 July 2021.
21. ^ Olson, Vickie (2015-04-15). "How to Select a pH Sensor for Harsh Process Environments". automation.isa.org. International Society for Automation. Retrieved 31 March 2017.
22. ^ AK Yetisen; H Butt; F da Cruz Vasconcellos; Y Montelongo; CAB Davidson; J Blyth; JB Carmody; S Vignolini; U Steiner; JJ Baumberg; TD Wilkinson; CR Lowe (2013). "Light-Directed Writing of Chemically Tunable Narrow-Ring Holographic Sensors". Advanced Optical Materials. 2 (3): 250. doi:10.1002/adom.201300375.
23. ^ "pH Electrode". pH-meter.info . Retrieved 30 March 2017.
24. ^ ^{a b} Travis, Anthony Southward.; Schröter, H.Chiliad.; Homburg, East.; Morris, P.J.T. (1998). Determinants in the evolution of the European chemical manufacture : 1900-1939 : new technologies, political frameworks, markets and companies. Dordrecht: Kluwer Acad. Publ. p. 332. ISBN978-0-7923-4890-0 . Retrieved 29 May 2015.
25. ^ ^{a b} Arnold Thackray & Minor Myers, Jr. (2000). Arnold O. Beckman : one hundred years of excellence. foreword by James D. Watson. Philadelphia, Pa.: Chemical Heritage Foundation. ISBN978-0-941901-23-ix.
26. ^ ^{a b} "Development of the Beckman pH Meter". National Celebrated Chemic Landmarks. American Chemic Society. Retrieved March 25, 2013.
27. ^ Luther, Claudia (May 19, 2004). "Arnold O. Beckman, 104". Chicago Tribune News . Retrieved 8 March 2014.
28. ^ Jaehnig, Kenton Grand. Finding Aid to the Beckman Historical Collection 1911 - 2011 (Bulk 1935 - 2004 ). Science History Constitute. Scientific discipline History Institute. Retrieved 30 October 2015. Click on 'Beckman Historical Collection Finding Aid' to become to full certificate.
29. ^ 15.iii.1957: English language Patent – Measuring assemblies for the determination of ion concentrations and redox potentials, particularly suitable for carrying out measurements at elevated temperatures. Patent No. 850177
30. ^ Dr. A. Fiechter, Dr. Westward. Ingold und A. Baerfuss, Chemie-Ingenieur-Technik ten (1964) 1000-1004: "Die pH-Kontrolle in der mikrobiologischen Verfahrenstechnik"
31. ^ "Here'southward the new Beckman Pocket pH Meter". Science History Plant. 1956. Retrieved vi Baronial 2019.
32. ^ Buie, John. "Evolution of the pH Meter". Lab Director . Retrieved October 7, 2010.
33. ^ "Building the Simplest Possible pH Meter". 66pacific.com . Retrieved 29 March 2017.

External links [edit]

Wikimedia Commons has media related to pH meters.

• Introduction to pH measurement – Overview of pH and pH measurement at the Omega Engineering science website
• Development of the Beckman pH Meter – National Celebrated Chemical Landmark of the American Chemical Gild
• pH Measurement Handbook - A publication of the Thermo-Scientific Co.

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Source: https://en.wikipedia.org/wiki/PH_meter

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