DOCSLIB.ORG

Ph Meters and Their Electrodes: Calibration, Maintenance and Use

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Ph Meters and Their Electrodes: Calibration, Maintenance and Use ARTICLE BACK TO BASICS pH meters and their electrodes: calibration, maintenance and use lithium-based glass electrodes are now used Following consideration of centrifugation and liquid handling in the exclusively for pH-responsive glass electrodes. February and March issues, respectively, of The Biomedical Scientist, POTENTIOMETRIC MEASUREMENT Almost all conductors of electricity are Peter Riddle now directs attention to pH meters, their electrodes and metal or an electrolyte, with the current being carried by either electrons or ions. the measurement of hydrogen ion concentration. When current passes from metal to electrolyte, or from electrolyte to metal, the type of carrier usually changes suddenly, and As living processes are dependent on the around 1928 the first commercial pH meter whenever there is an interface between the unique ionising solvent we know as water, was produced by the Cambridge Instrument metal and ions of that metal in a solution and as much of classical chemistry was Company. Both electrodes were subject to then an electric potential is produced. concerned with the study of reactions in interference from the components of redox This potential is called the electric potential aqueous solution, the ubiquity of the pH systems that reduced the effectiveness of of that metal. An electrode potential is also meter in present-day biomedical laboratories these electrodes to measure the potential produced when different concentrations of is scarcely surprising. The concept of response due to hydrogen ions. Membrane an ion are separated by a membrane that is electrolytic dissociation was introduced over electrodes, including the glass electrode, semipermeable to that ion. Non-metallic a century ago by Arrhenius, and in 1909 are not subject to these limitations and elements such as hydrogen also have Sorenson demonstrated the importance of electrode potentials. hydrogen ion concentration on enzyme In order to measure an electrode potential, activity and coined the term ‘pH’. Although ‘The hydrogen electrode another voltage source (such as another that same year saw the first systematic study metal/solution interface) is needed to of the glass electrode, it was not until the was the first electrode to be measure it against. Each of the electrodes is development of convenient electronic called a half-cell. The two half-cells arranged techniques capable of accommodating the used for pH measurement together constitute an electrochemical cell, high electrical resistance of the glass in which one of the half-cells maintains a electrode that interest in electrometric pH but it required a supply of constant voltage. The electrode in the half- determination and its importance in cell with the constant voltage is called the biological systems became clear. hydrogen gas and thus its reference electrode, whereas the variable The pH meter is designed to measure the voltage portion is termed the indicator concentration of hydrogen ions in a solution. application was limited’ electrode. It is possible to measure the Basically, three parameters are involved in the measurement: the actual molar concentration of hydrogen ions, the dissociation constant of the acid (pKa), and temperature. pH is Glass Test or standard KCl/Hg Cl /Hg defined as the negative of the logarithm to Ag/AgCl/HCl 2 2 membrane membrane the base 10 of the hydrogen ion concentration (pH = –log10 [H+]). The hydrogen electrode was the first electrode to be used for pH measurement but Indicator glass electrode Reference electrode it required a supply of hydrogen gas and thus its application was limited. The quinhydrone Fig 1. The composition of the two half-cells that permits the electrode appeared in the early 1920s and difference in potential to be detected between them. 202 THE BIOMEDICAL SCIENTIST APRIL 2013 ARTICLE Wire connection point Wire connection point Glass body Glass or plastic body Seal Filled with Silver potassium chloride wire ‘buffer’ solution Silver wire Bulb filled with – + + – Very thin glass potassium – + + – bulb chemically chloride ‘buffer’ – + + – ‘doped’ with solution Silver – + + – lithium ions so as Silver + chloride tip + to react with – – chloride tip + + hydrogen ions – + + + + + – Porous junction – – outside the bulb – – – Voltage produced across thickness of the glass membrane Fig 2. The reference electrode. Fig 3. The indicator (glass) electrode. potential difference between these two concentration through the Nernst equation, is desired, a 0.1 mol/L or 1 mol/L potassium electrodes and calculate the concentration which, in its simple form, is E=KT log chloride solution electrode is preferred of ions in the solution of the indicator (C1/C2) where K = Constant 2.3 (R/zF) because it reaches its equilibrium potential (measuring) electrode. and if either C1 or C2 is known then the more quickly and its potential depends less For example, if a silver wire is immersed in concentration can be calculated from the on temperature than does the saturated type. a solution of silver chloride, ionisation of the measurement of the potential developed. The silver–silver chloride electrode is a very silver metal occurs, with the formation of In making an electrical connection reproducible electrode. The solution silver ions (Ag+) and electrons. An electric between the reference electrode and the surrounding the electrode should be potential now exists between the wire and the sample solution via a salt bridge, a negligible saturated with potassium chloride and silver solution. If two half-cells are used, each with a but reproducible potential is produced. This chloride. silver wire or foil immersed in a different silver potential develops at the interface between solution, and the two solutions are connected two non-identical solutions and is called the INDICATOR ELECTRODES through a meter, a difference in potential liquid–liquid junction potential. A saturated The glass electrode was the first and still most can be detected between them (Fig 1). potassium chloride solution is normally used commonly used electrode for measuring As the potential of each solution depends on as a salt bridge in the reference electrode hydrogen ion activity. A glass electrode consists the concentration of silver ions in it, the because many ions diffuse from the salt of a small bulb of special glass that contains a concentration of ions in one solution can be bridge against which the sample ions must solution of known hydrogen ion concentration predicted if the value for the other solution diffuse. Thus, diffusion of ions from the (eg 0.1N HCL or KCL ‘buffer solution’) and an and the difference in potential between sample to the junction is negligible and the internal reference electrode (usually calomel them are known. A temperature difference junction potential is ≤1 mV and is or silver–silver chloride; Fig 3). The sensor is between the two half-cells would affect the reproducible. normally a platinum wire. reproducibility of measurement. Other minor The pH electrode is manufactured with technical factors, such as coating (eg protein), REFERENCE ELECTRODES different properties, depending on the will affect the measurements. The standard hydrogen electrode is the application. Those used in biomedical Potentiometric methods are based on international standard but is seldom used for laboratories should be linear at about pH 7.0. the quantitative relationship between the routine work because a supply of hydrogen Wide-range pH electrodes (1–14) tend to be potential of a cell as given by the following gas is required and more convenient types non-linear towards the ends of the range. distribution of potential: (together with reliable calibration buffers) are Some are designed to be linear for low pH E = E + E + E available. The saturated calomel electrode values, while others are linear for high pH cell reference indicator junction is a widely used reference electrode that values. These properties are controlled by the Because the reference and junction potentials contains an inert element (eg platinum) in glass formula. are constant, the indicator potential can be contact with mercury, mercurous chloride determined. The potential of the indicator (calomel) and a solution of potassium COMBINATION ELECTRODE electrode can then be related to chloride of known concentration. However, It is inconvenient in many applications to concentration. Electrode systems used in in view of environmental considerations, the have to contend with two measuring biomedical laboratories have precalibrated mercury electrode is rarely used these days electrodes (reference and indicator). read-out devices that give results in and such electrodes are not suitable for Combination electrodes are available into concentration units. varying temperatures or temperatures above which both the reference (usually Ag–AgCl) The cell potential is related to 60˚C (Fig 2). When a high degree of accuracy and indicator electrodes are incorporated. APRIL 2013 THE BIOMEDICAL SCIENTIST 203 ARTICLE The pH membrane is usually recessed in, ‘Both standard moving-pointer INSTRUMENT CALIBRATION and protected by, a plastic housing. Such It is essential that pH electrodes are electrodes will withstand more physical abuse meters and digital display calibrated regularly using the meter and than will conventional pH electrodes. reference electrode with which they are to be The pH of a solution is a function of its units are common, although used in the laboratory. The procedure is as temperature. Voltage output from the follows:
Load more

Recommended publications
  • Measuring Soil Ph
    Measuring soil pH Viti-note Summary: Soil pH refers to the acidity or alkalinity Equipment of the soil. It is a measure of the • Equipment Colorimetric test kit available from concentration of free hydrogen ions nurseries (includes mixing stick, plate, • Timing (H+) that are in the soil. Soil pH can dye, barium sulphate, pH colour chart, be measured in water (pH ) or a weak • Method w instructions), teaspoon, recording sheet calcium chloride solution (pH ). The pH CaCl and pen. • Timing range is from 0-14, with value of 7 being neutral. Soil pH values (as measured in a OR water and soil solution) indicate: Hand held pH meter, clear plastic jar with • Strong acidity if less than 5.0. screw-on lid, distilled water, recording sheet and pen. • Moderate acidity at 5.0 to 6.0. • Neutral between 6.5 and 7.5. Timing • Moderate alkalinity at 7.5 to 8.5. This measurement is best undertaken • Strong alkalinity for values of 8.5 when soil sampling is conducted and and above. would normally be done at the same time The limited data available suggests that as assessments for electrical conductivity. soil pHCaCl should be in the range 5.5-7.5 Soil pH should be measured in the fibrous for best vine performance. root zone (ie. 0-20cm depth) as well as Soil pH outside the neutral range can the deeper root zone (>20cm depth). influence the availability of specific Make sure the soil samples are taken nutrients to plants, as well as the inside the irrigation wetting pattern.
    [Show full text]
  • Ph Meter Guide Ph Is a Measurement of Acidity Or Alkalinity in a Food Using a Numerical Scale from 1 to 14
    FACT SHEET #31 pH Meter Guide pH is a measurement of acidity or alkalinity in a food using a numerical scale from 1 to 14. A pH below 7 is acidic, a pH of 7 is neutral, and a pH value above 7 is basic or alkaline. Monitoring pH levels during food processing is an important step in the production of some food since pH values affect microbial growth. Acidity and pH • Electrode: It is the part of the pH meter immersed in the sample. Select an electrode suitable for the food The acidity of food can be determined by measuring you are testing. For instance, some electrodes have its pH value. To preserve food with only acidity, it spear tips that are more suitable for measuring the pH needs to have an equilibrium pH value of 4.6 or lower. of semi-solid food. Equilibrium pH is the pH of a food after all components Use: of the food have achieved the same acidity. • Bench top models are suitable for laboratory use. If the pH meter will be taken into the plant, then a Foods with a pH greater than 4.6 are considered low handheld model may be more appropriate. acid foods. Foods with a pH less than 4.6 can be called acid foods. An acidified food is a low acid food Temperature with acidic ingredients added to it to lower the pH (ex: vinegar). Temperature can affect pH readings. To get an accurate reading, the pH meter must be calibrated at the same pH and micro-organisms temperature as the samples being tested.
    [Show full text]
  • Developing a Non-Glass Ph Meter John Lyon Dr Raouf Selim
    Developing a Non-Glass pH Meter John Lyon Dr Raouf Selim PCSE 498 Physics Capstone Project Fall 2014 - Spring 2015 Abstract I intended to develop and test a non-glass pH meter using an ion-selective field effect transistor (ISFET) for this project. The meter would have consisted of the ISFET, a reference electrode, and a voltmeter. The measurements made by this meter should agree with the Nernst equation which relates pH to potential difference. Unfortunately, materials for this project were very hard to come by, most notably, the ISFET itself. In lieu of this situation, I built a glass pH electrode instead. I used a test tube, potassium chloride, and silver wire to make the glass electrode. Upon building this meter, I found that the readings produced were very random and gave no conclusive results on how well the pH meter worked. Introduction I am interested in measuring the pH of a solution over a prolonged period of time. I decided that a non-glass pH meter would be appropriate because it does not contain a liquid solution within it. After some research about pH meters, I discovered that all potentiometric pH meters have a reference electrode, and generally these electrodes contain a reference solution, so my non-glass meter might still require this reference solution. Because I did not want to have an internal solution in my pH meter, I thought it would be interesting to develop a simulated reference electrode along with the non-glass electrode. The non-glass electrode to be used would be an ion-selective field effect transistor (ISFET) electrode.
    [Show full text]
  • 2105 Soilstik
    ® SoilStik pH Meter PRODUCT MANUAL Item # 2105 2 Contents General Overview .....................................3 LCD Display................................................4 LCD Display Messages ............................5 Meter Components ...................................6 Calibration .................................................7 Changing the Temperature Units.............8 Taking Liquid/Soil Measurements ...........9 Storing/Recalling Measurements...........10 Sensor Replacement ...............................11 Battery Replacement...............................12 Meter Handling/Troubleshooting ..........13 Specifications .........................................14 Warranty ...................................................15 This manual will familiarize you with the features and operation of your new meter. Please read this manual thoroughly before using your meter. For customer support or to place an order, contact Spectrum Technologies, Inc between 7:30 a.m. and 5:30 p.m. CST. Phone: (800) 248-8873 or (815) 436-4440 Fax: (815) 436-4460 E-mail: [email protected] Website: www.specmeters.com Spectrum Technologies 12360 S. Industrial Dr. East Plainfield, IL 60585 3 General Overview Congratulations on the purchase of your Field Scout™ SoilStik™ Pro Meter. This manual describes how to use your pH meter and keep it working accurately. Read the manual thoroughly in order to make effective use of your meter. The SoilStik delivers high quality answers, with an accuracy of +/- 0.01 pH units. This self-contained digital meter allows you to test the pH levels in water, soil, and other liquids. The replaceable sensor makes the measurement of small samples much more convenient. The sensor provides a visual indication of when replacement is due. The meter has a two-point, automatic calibration (pH 4 and 7), with a range of pH 2.0-12.0. The display will show your results to a resolution of 0.01 pH units.
    [Show full text]
  • Chapter 3 Ph Meter
    MAINTENANCE MANUAL FOR LABORATORY EQUIPMENT Chapter 3 pH Meter GMDN Code 15164 ECRI Code 15-164 Denomination pH Meter The pH meter is used for determining the concentration of PHOTOGRAPH AND COMPONENTS OF THE hydrogen ions [H+] in a solution. This equipment, provided pH METER it is carefully used and calibrated, measures the acidity of an aqueous solution. pH meters are sometimes called pH analysers, pH monitors or potentiometers. 2 1 PURPOSE OF THE EQUIPMENT The pH meter is commonly used in any field of science related to aqueous solutions. It is used in areas such as agriculture, water treatment and purifi cation, in industrial processes such as petrochemicals, paper manufacture, foods, pharmaceuticals, research and development, metal mechanics, etc. In the health laboratory, its applications are related to the control of culture mediums and to the measurement of the alkalinity or acidity of broths and buff ers. In specialized laboratories, diagnostic equipment microelectrodes are used to measure the pH of liquid blood components. The plasma pH allows the patient’s health to be evaluated. It normally measures between 7.35 3 and 7.45. This value relates to the patient’s metabolism in which a multitude of reactions occurs where acids and 1 Electrode carrying arm and electrode bases are normally kept in balance. Acids constantly liberate 2 Digital display + 3 Control panel with temperature adjustment control, mode hydrogen ions [H ] and the organism neutralizes or balances selection (Standby/mV/pH) and calibration controls – acidity by liberating bicarbonate ions [HCO3 ]. The acid-base ratio in the organism is maintained by the kidneys, (organs courtesyPhoto of Consort in which any excesses present are eliminated).
    [Show full text]
  • Buffers and Titrations
    Chapter 2: Buffers and Titrations Purpose: 1) Get to know your pH meter 2) Make a common buffer used in biochemistry and perform titrations of that buffer with acid or base to find the pKa values for the buffer 3) Hydrolyze BSA with trypsin and calculate the number of Lys and Arg residues that BSA contains pH Meter ● Glass-electrode sensitive to hydrogen ions ● Electrode somewhat sensitive to other alkali metals ● Complete system contains: ● Electrometer – 5 ● Reference Electrode – 6 ● Solution to be measured – 1,4 ● Glass Electrode – 2,3 Titration Curves in Non-buffered Solutions Weak Acid = ● Equivalence Point 0.1 M Acetic Acid ● Point at which reaction is Strong Acid = neutralized 0.1 M Hydrochloric Acid ● Inflection point in titration curve ● Strong Acid – pH 7.0 ● Weak Acid – pH 8.8 ● Buffered solutions behave as weak acids ● Table of pKa values – Lab Manual p. 36 pH Changes in Buffered Solutions pKa of Buffer + More H More -OH present present Begin deprotonating buffer Titration ends Titration begins Add Fully deprotonated buffer with an acidic pH -OH at basic pH Acidic pH of the Solution Basic Buffered Titration Curve Titration of a Buffer 8 ● Modeled on 7 Henderson- Hasselbach 6 equation 5 4 pH 3 2 1 0 0 20 40 60 80 100 120 Quantities of -OH Added Buffered Titration Curve Titration of a Buffer 8 ● Empirically, H-H 7 equation useful 6 for buffering 5 range 4 ● Buffers most pH 3 effective near pKa 2 1 0 0 20 40 60 80 100 120 Quantities of -OH Added - pH = pKa when [A ] = [HA] Buffering Capacity ● Ability of buffer to resist changes
    [Show full text]
  • Ph, Conductivity/TDS & DO Meters
    M pH, Conductivity/TDS & DO Meters POCKET PAL METERS® Handheld, lab accurate and modestly priced, the Pocket Pal meters are an industrial standard. Pocket Pal series elec- trodes are field replaceable and usually can be changed and calibrated in a matter of minutes. Digital displays, rugged ABS plastic housings and precision two-point calibration potentiometers make all seven Pocket Pals perfect for field, plant or laboratory use. With Automatic Temperature Compensation standard (except PH-2), accurate response is just seconds away. Each Pocket Pal comes equipped with a 9-volt battery, calibration screwdriver, instruction card and a handy belt loop case. DUAL pH & CONDUCTIVITY - THE MOST POPULAR POCKET PAL METER DSPH-1 and DSPH-3 POCKET PAL meters measure pH and conductivity in a compact one-hand operation. There are no electrode cables to fool with. The electrodes simply fold under the instrument for storage. Two test buttons control all opera- tions. Temperature variations are automatically compensated for both pH and conductivity measurements. Easy screwdriv- er adjustments include Cal and Slope for pH, and Zero and Span for conductivity. The POCKET PAL operates on a 9-volt Water Quality / Analytical Water battery (included). DSPH-1/DSPH-3 METER Dimensions (Electrodes folded): For versatility in the field or the laboratory, the 159 mm L X 32 mm D (6.25" X 1,25"; DSPH-1US/1PPM and DSPH-3US/3PPM fea- 32 mm W (1.25") Handle; 57 mm W (2.25") LCD ture pH, conductivity and total dissolved solids Electrode Lengths (vertical or horizontal): measurements in one handheld instrument. The * 127 mm L (5"); 9.5 mm dia (3/8") DSPH-1US/1PPM measures pH from 0-14 and Power: One 9 V battery conductivity from 0 to19,999 in μmhos or ppm, *(Electrodes are independently interchange- and the DSPH-3US/3PPM extends the conduc- able by the user) tivity measuring range to 199,999 in μmhos or ppm.
    [Show full text]
  • 6. Soil Ph Test
    6. Soil pH Test Use the same soil-water mixture prepared in the EC test to conduct the pH Test. If you are start- ing with a fresh soil sample, read the introduction and follow Steps 1-3 in the EC Test Chapter on preparing the sample. Materials needed to measure pH: Did You Know? • 1/8-cup (30 mL) measuring scoop Soil acidification can also be an • plastic specimen bottle indication of excessive N fertilizer • calibration buffer solutions applications and N leaching loss. • squirt bottle • pH pocket meter (red with black cap) • distilled water Considerations: If the soil sample is saturated or very wet, a 1:1 ratio, on a volume basis, of soil to water will not be obtained in the soil-water mixture (See Step 2, Chapter 5). Let the soil dry before proceeding with Step 1 in Chapter 5. Also, a small amount of salts diffuse out of the pocket pH meter; therefore, EC measurements should always be taken first when measuring both EC and pH on the same sample. 1 Measure and Record pH • Make sure to periodically calibrate your pH meter (See Appendix C for instructions). If the meter has not been used in a while, place the meter in tap water for about 5 minutes before calibrating or taking a reading. • Wait about 10 to 15 minutes after the EC measurement before measuring the pH. This gives the soil particles time to settle. Insert the pH pocket meter into the topmost portion of the solution and turn the meter on. Wait until the reading stabilizes (0-30 seconds), and record the digital reading on the Soil Data worksheet.
    [Show full text]
  • IQ140 Ph Meter-User#19F7930
    Telephone: 760 930-6501 Fax: 760 930-0615 IQ Scientific Instruments, Inc. www.phmeters.com 2075-E Corte del Nogal Carlsbad, CA 92011 Revision 4.5 2005 IQ Scientific Instruments, Inc. MODEL IQ140 pH Meter Getting Started TWO-POINT CALIBRATION--QUICK REFERENCE GUIDE 1. 2. 3. 4. Connect probe to Put probe in first Press ON/OFF to If necessary, press meter. calibrating buffer. turn on meter. pH until pH icon is seen on the display. 5. 6. 7. 8. Press CAL. If necessary, press Press ENTER and When complete, SELECT BUFFER wait until the large meter will display until display matches number display the next stored first buffer value. stops flashing. buffer value. 2PT will be displayed. 9. 10. 11. 12. Rinse probe in If necessary, press Press ENTER and Rinse probe in deionized water SELECT BUFFER wait until the large deionized water and and place in until display matches number display place in sample. second calibrating second buffer value. stops flashing. buffer. 1 INTRODUCTION IMPORTANT NOTICE IF THE METER IS USED IN A MANNER OTHER THAN AS DESCRIBED, THE SAFETY AND PERFORMANCE OF THE METER CAN BE IMPAIRED. IF THE SEAL ON THE BACK OF THE METER IS TAMPERED WITH, THE WARRANTY IS IMMEDIATELY VOIDED. The IQ140 pH/mV/Temperature meter accepts conventional glass sensor electrodes with BNC connectors. The meter has a standard BNC connector for attachment of glass sensor pH electrodes and a 3.5 mm phono jack for attaching a 30K_ thermistor. Contact IQ Scientific Instruments for convenient “3-in-1” pH electrodes that include the pH sensor and a built-in temperature sensor.
    [Show full text]
  • 4500-H Ph VALUE* 4500-H A. Introduction 4500-H B
    4-90 INORGANIC NONMETALS (4000) 4500-Hϩ pH VALUE* 4500-Hϩ A. Introduction 1. Principles alence to molarity, [Hϩ] can be presumed only in very dilute solutions (ionic strength Ͻ0.1). Measurement of pH is one of the most important and fre- A logarithmic scale is convenient for expressing a wide range quently used tests in water chemistry. Practically every phase of of ionic activities. Equation 1 in logarithmic form and corrected water supply and wastewater treatment, e.g., acid-base neutral- to reflect activity is: ization, water softening, precipitation, coagulation, disinfection, Ϫ ϩ Ϫ Ϫ ϭ ( log a ϩ) ( log a ) 14 (2) and corrosion control, is pH-dependent. pH is used in alkalinity 10 H 10 OH and carbon dioxide measurements and many other acid-base equilibria. At a given temperature the intensity of the acidic or or ϩ ϭ basic character of a solution is indicated by pH or hydrogen ion pH pOH pKw activity. Alkalinity and acidity are the acid- and base-neutraliz- ing capacities of a water and usually are expressed as milligrams where: CaCO per liter. Buffer capacity is the amount of strong acid or ϭ 3 pH† log10 aHϩ and base, usually expressed in moles per liter, needed to change the ϭ Ϫ pOH log10 aOH . pH value of a 1-L sample by 1 unit. pH as defined by Sorenson1 is Ϫlog [Hϩ]; it is the “intensity” factor of acidity. Pure water is Equation 2 states that as pH increases pOH decreases very slightly ionized and at equilibrium the ion product is correspondingly and vice versa because pKw is constant for a given temperature.
    [Show full text]
  • Essentials of Ph Measurement
    Essentials of pH Measurement Tim Meirose, Technical Sales Manager Thermo Scientific Electrochemistry Products The world leader in serving science What is pH? • The Theoretical Definition pH = - log aH • aH is the free hydrogen ion activity in a sample, not total ions. • In solutions that contain other ions, activity and concentration are not the same. The activity is an effective concentration of hydrogen ions, rather than the true concentration; it accounts for the fact that other ions surrounding the hydrogen ions will shield them and affect their ability to participate in chemical reactions. • These other ions effectively change the hydrogen ion concentration in any process that involves H+. pH electrodes are an ISE for hydrogen. 2 What is pH? • pH = “Potential Hydrogen” or Power of Hydrogen • The pH of pure water around room temperature is about 7. This is considered "neutral" because the concentration of hydrogen ions (H+) is exactly equal to the concentration of hydroxide (OH-) ions produced by dissociation of the water. • Increasing the concentration of H+ in relation to OH- produces a solution with a pH of less than 7, and the solution is considered "acidic". • Decreasing the concentration H+ in relation to OH- produces a solution with a pH above 7, and the solution is considered "alkaline" or "basic". OH- + H+ - H OH - + - OH H+ H OH H+ H+ H+ - OH OH- H+ OH- OH- + - LOW pH = LOTS OF H LOTS OF OH = HIGH pH 3 What is pH? Representative pH values • The pH Scale Substance pH Hydrochloric Acid, 10M -1.0 Lead-acid battery 0.5 Gastric acid 1.5 – 2.0 • Each pH unit is a factor 10 in Lemon juice 2.4 + [H ] Cola 2.5 • pH of Cola is about 2.5.
    [Show full text]
  • TWS-INC-DP-35, R1 Ph MEASUREMENT Effective Date
    , TWS-INC-DP-35, R1 pH MEASUREMENT Effective Date: 31,3/mI DATE PREPARED& DATE TECHNICAL APPROVAL DATE INC DIVISION QA REPRESENTATIVE / 0/ TECU?6 CAL PROJECT OFFICER DATE DATE 8912190162 891211 'PDR, WASTE WM-11 PDC TWS-IN.\C-DP-35. R1 Page 1 of 5 pH MEASUREMIENT I. PROCEDURE IDENTIFIER: TWS-INC-DP-35 INTRODUCTION 2. PURPOSE This procedure leads to the accurate determination of the pH or hydrogen ion activity of a solution given by the relationship pH = -log(aH+) 3. SCOPE This procedure may be used to measure the pH of an aqueous solution for any task in the LANL Yucca Mountain Project (YMP). 4. APPLICABLE DOCUMENTS a. TWVS-QAS-QP-05.2 "Preparation of a Detailed Technical Procedure" b. TWS-QAS-QP-ot "Procedure for Technical Review of Publications" c. TWS-MSTQA-QP-14 "Research and Development (Experimental) Procedure" d. The user's manual (or a copy) for the pH meter and electrode to be used are required and will be kept with the instrument. 5. RESPONSIBILITIES The PI has the responsibility of organizing and overseeing all operations. He may assign appropriate tasks to personnel trained to this DP. It is the responsibility of the users of this DP to adhere to the procedure. Investigators may direct deviations from the procedure upon approval of the responsible PI. It is the responsibility of the user to TWS-INC-DP-35, R1 Page 2 of 5 document such deviations in accordance with TWS-MSTQA-QP-14. If change requests are in process it is the responsibility of the user to document the procedure change in the laboratory notebook.
    [Show full text]