pH

  1. Titration - Manual Procedure

    Titration - Manual Procedure

    Titration is a procedure in which a solution – called the titrant – whose concentration is known very accurately is dispensed by a burette and reacted with a known volume of another solution of unknown concentration – called the analyte. By measuring the amount of titrant needed to neutralize the analyte, you can determine the concentration of the analyte very accurately.The "end point" of a titration is the point at which the titration is complete, typically when an added indicator solution such as phenolphthalein changes color. The "equivalence point" is closely related to but not necessarily identical with the end point. The equivalence point is the point at which the number of moles (or equivalents) of titrant exactly equals the number of moles (or equivalents) of analyte.Ideally, the end point should exactly equal the equivalence point, but in the real world they are slightly different. For example, you may titrate a hydrochloric acid analyte with a sodium hydroxide titrant, using phenolphthalein as an indicator. Phenolphthalein is colorless in acid solutions, and pink in base solutions, but no color change occurs until the pH of the solution reaches about 8.2, well into the basic range.
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  2. Cleaning and Reconditioning pHTestr Series Electrodes

    Cleaning and Reconditioning pHTestr Series Electrodes

    Oakton Tech Tips Cleaning and Reconditioning pHTestr Series Electrodes Tech Tip #3 ©1997 Often, the OAKTON® pHTestrs are used in applications which require regular cleaning of the electrode or reference. These applications involve very hard waters (i.e. those with high scale content), dirty samples like soil slurries, viscous materials or samples with high oil and protein content.
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  3. pH Measurement

    pH Measurement

    pH measurement is used in a wide variety of applications: agriculture, wastewater treatment, industrial processes, environmental monitoring, and in research and development. pH is a measure of the acidity or alkalinity of a solution. The pH value states the relative quantity of hydrogen ions (H+) contained in a solution. The greater the concentration of H+ the more acidic the solution and the lower the pH. In this relationship, pH is defined as the negative logarithm of hydrogen activity. A standard pH measuring system consists of three elements: 1) pH electrode; 2) temperature compensation element and 3) pH meter or controller.
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  4. A Definition of pH

    A Definition of pH

    One method used to describe chemicals is pH or "potential of hydrogen". A universally accepted scale for pH that describes chemicals as either "acidic" or "basic" is employed. This pH scale ranges from 0 to 14 with a pH of 7 being neutral; a pH less than 7 being acidic; and a pH greater than 7 being basic. For example, when the value begins at 7.0 and moves toward 0, acidity is indicated.
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  5. Temperature Compensation for pH Instruments

    Temperature Compensation for pH Instruments

    Oakton Tech Tips Temperature Compensation for pH Instruments Tech Tip #11 ©1997   Although it is widely advertised, the need for temperature compensated pH measurements is not always explained  except in technical books and articles. This Tech-Tip will give a brief explanation of the major characteristics of temperature compensation in pH instruments.
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  6. Top Ten frequently asked questions for pHTestrs

    Top Ten frequently asked questions for pHTestrs

    Top Ten frequently asked questions for pHTestrs Tech Tip #21 ©1997   1.  Why won’t my pHTestr turn on? Possible reasons: batteries improperly installed or dead. Possibly keypad is defective. Remedy: reinstall batteries or install new batteries. Replace the pHTestr.  
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  7. Calibrating ORP measurement systems

    Calibrating ORP measurement systems

    Background Like pH, Conductivity/TDS, and other electrochemical measurements, ORP measurements are based on displaying the response of a specialized electrode in a solution. Like pH electrodes, each ORP electrode has unique characteristics that cause variability in the signal the electrodes send to the meter. Both the offset and slope characteristics of the pH electrode must be compensated by calibration to the meter in order to obtain accurate readings. ORP electrodes and measurements present different problems.
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  8. An Introduction to ORP

    An Introduction to ORP

    OAKTON Tech Tip #13 ©1997 Oxidation-Reduction Potential (ORP) or Redox potential measurements are used to monitor chemicalreactions, to quantify ion activity, or to determine the oxidizing or reducing properties of a solution.  ORP is the measurement of the electrical potential of a redox reaction and serves as a yardstick to judge how much oxidation or eduction takes place under existing conditions. ORP electrodes measure the voltage across a circuit formed by the measuring metal half cell and the reference half cell. When the ORP electrode is placed in the presence of oxidizing or reducing agents, electrons are constantly transferred back and forth on its measuring surface, generating a tiny voltage. The ORP measurement can be made using the millivolt mode of a pH meter.  
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  9. Measuring pH of Pure Water

    Measuring pH of Pure Water

    "What could possibly be so difficult about reading the pH of pure water? It should be neutral-pH7.0, and there are no interference’s", common sense says. In practice, it can be quite difficult and often frustrating to obtain reproducible pH values in samples with low-ionic strength. Water that has very few ionic species is said to be low in alkalinity, ionic strength, or have low conductivity/highresistivity such as distilled or deionized (DI) water. It is common to attain different pH values with new, sealed electrodes that calibrate perfectly in pH buffers when attempting to measure DI water.  This is due to the varying junction potentials that develop across the reference junction. Some techniques and product recommendations for overcoming such limitations will be discussed here. 
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  10. Dissolved Oxygen

    Dissolved Oxygen

    Dissolved Oxygen Measurement   Oxygen is one of the essential elements for the existence of life, but life can only exist when the concentration of oxygen falls within certain limits. When measuring oxygen in aquatic environments we are actually measuring the amount of oxygen dissolved in the water; thus the name Dissolved Oxygen or DO for short. The level of DO in water depends on many physical, chemical, and biochemical activities in the sample or at the sample site. The three most important factors to consider are temperature, pressure, and salinity. The amount of oxygen a given sample can hold in solution will vary with the temperature of the sample, the pressure or altitude at which the sample is measured, and the concentration of salts dissolved in the sample.  The analysis of DO is one of the key tests performed in water pollution studies and at waste water treatment facilities. Some other areas where the analysis of dissolved oxygen is important are aquaculture (fish farming), aquatic environments such as fish ponds or aquariums, water quality testing, surface and ground water surveys, and evaluating the safety of potable water.
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