pH Theory Guide - 19 Pages

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pH Theory Guide

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Mettler-Toledo AG Process Analytics Industry Environment A Guide to pH Measurement – the Theory and Practice of pH Applications

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the Theory and Practice of pH Applications METTLER^ TOLEDO

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Copyright © 2013 by Mettler-Toledo AG CH-8902 Urdorf/Switzerland

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Content Preface 1 Introduction to pH 1.1 Acidic or alkaline? 1.2 Why are pH values measured? 1.3 The tools for pH measurements 1.3.1 The pH electrode 1.3.2 Reference electrodes 1.3.3 Combination electrodes 1.4 What is a pH measuring system? 2 Practical considerations 2.1 The pH ­ easuring system m 2.2 Obtaining an accurate pH measurement 2.2.1 General principles of pH measurement 2.2.2 Industrial pH measurement 2.2.3 Signal processing and environmental influences 2.2.4 Calibration 2.2.5 Buffer solutions 2.3 How to maintain a reliable signal 2.3.1 Maintenance of the electrode function 2.3.2...

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4 Electrode selection and handling 4.1 Different kinds of junction 4.1.1 Ceramic junctions 4.1.2 PTFE annular diaphragm 4.1.3 Open junctions 4.1.4 Dual-membrane without junction 4.2 Reference ­ ystems and electrolytes s ­ 4.3 Types of ­ embrane glass and membrane shape m 4.4 pH electrodes for specific applications ­ 4.4.1 Highly accurate problem solver 4.4.2 Complex samples or such of unknown ­ composition 4.4.3 Semi-solid or solid samples 4.4.4 At the toughest applications in chemical p ­ rocess ­ndustries i 4.4.5 Prepressurized electrolyte pH electrodes 4.4.6 Dual-membrane pH electrodes...

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5 Comprehensive pH theory 5.1 Definition of the pH value 5.2 Correlation of concentration and activity 5.3 Buffer solutions 5.3.1 Buffer capacity (ß) 5.3.2 Dilution value (∆pH) 5.3.3 Temperature effect (∆pH / ∆T) 5.4 The measurement chain in the pH measurement setup 5.4.1 pH electrode 5.4.2 Reference electrode 5.5 Calibration / adjustment of the pH measurement setup 5.6 The influence of temperature on pH measurements 5.6.1 Temperature dependence of the electrode 5.6.2 Isothermal intersection 5.6.3 Further temperature phenomena 5.6.4 Temperature dependence of the measured sample 5.7...

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Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 Figure 27 Figure 28 8 pH Theory Guide METTLER TOLEDO The reaction of an acid and a base forms water Dissociation of acetic acid The formula for calculating the pH value from the concentration of hydronium ions pH values for some chemicals and everyday products The reaction of ammonia with water The relationship between the amount of...

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Figure 29 Figure 30 Figure 31 Figure 32 Figure 33 Figure 34 Figure 35 Figure 36 Figure 37 Figure 38 Figure 39 Figure 40 Figure 41 Figure 42 Figure 43 Figure 44 Figure 45 Figure 46 Figure 47 Puncture pH electrode 61 InPro 480x (i) 62 InPro 325x (i) 63 InPro 4850 i 64 pHure Sensor™ 64 InPro 3100 (i) 65 InPro 3300 (ISFET pH sensor) 66 InPro 4501 66 InPro 4550 67 Buffering capacity of acetic acid 77 Temperature dependence for the pH electrode slope factor 79 Different sources of ­ otential in a combination electrode 79 p Ion mobility and diffusion of ions through a junction 82 Left: offset...

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Preface The aim of this book is to give a representative description of pH meas­ urement in the process industries. The actual sensor, the pH electrode, is therefore the main focus of the text. Correct sensor use is fundamental for a meaningful pH measurement. Accordingly, both practical and theoretical requirements are dis­ ussed in depth so that the measuring c principle is understood and an accurate measurement made possible. The first section (practical considerations) of the book describes the sensor, and the other elements that constitute a pH measurement system. Together with a...

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Acidic or alkaline? Why do we classify an everyday liquid like vinegar as being acidic? The reason is that vinegar contains an excess of hydronium ions (H3O+) and this excess of hydronium ions in a solution makes it acidic. An excess of hydroxyl ions (OH–) on the other hand makes something basic or alkaline. In pure water the hydroniumn ions are neutralized by hydroxyl ions, therefore this solution has a neutral pH value. H3O+ + OH– ↔ 2 H2O Figure 1 The reaction of an acid and a base forms water. If the molecules of a substance release hydrogen ions or protons through dissociation we call...

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The quantitative difference between acidic and alkaline substances can be determined by performing pH value measurements. A few e ­ xamples of pH values of everyday substances and chemicals are given in Figure 4 below. Food & Beverages / Household products Orange juice Cheese Coca Cola Acetic acid Sulfuric 0.6 % (0.1M) acid 4.9 % (1M) Hydrochloric acid Hydrocyanic acid 0.37 % (0.1M) 0.27 % (0.1M) Caustic soda 4 % Calcium carbonate (sat) Ammonia sol. 1.7 % (1M) Ammonia sol. 0.017 % (0.01M) Potassium acetate 0.98 % (0.1M) Sodium hydrogen carbonate 0.84 % (0.1M) pH values for some chemicals...

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Why are pH values measured? We measure pH for a lot of different reasons, such as: • to produce products with defined properties – During production it is important to control the pH to ensure that the end product conforms with the desired specifications. The pH can dramatically alter the properties of an end product such as appearance or taste. • to lower production costs – This is related to the above mentioned reason. If the yield of a certain production process is higher at a given pH, it follows that the costs of production are lower at this pH. • to avoid doing harm to people,...

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The tools for pH measurements To be able to measure pH you need to have a measurement tool which is sensitive to the hydrogen ions that define the pH value. The principle of the measurement is that you take a sensor with a glass membrane which is sensitive to hydrogen ions and observe the reaction between it and a sample solution. However, the observed potential of the pH-sensitive electrode alone does not provide enough information and so we need a second sensor. This is the sensor that supplies the reference signal or potential for the pH sensor. It is necessary to use the difference...

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