pH Meter Intro

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by MeaganLMalloy
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pH Meter Intro

pH Meter Intro

Types of pH Meters:Portable - Useful for measurements taken in the fieldBench - Most commonly for lab useOnline - used in extreme environments to take continual readings (ex. wastewater treatment plant discharge)

Common Sources of ErrorAcid/Alkaline error - if solution being tested is under pH 1 or above pH 12 Tempurature - electrodes are temperture sensativeDegraded electrode - if the electrode is not properly taken care of it will not measure the pH accuratelyLow ionic strength of solution - partial clogging of the porous fiber that is used to restrict the flow of liquid from the salt bridge into the analyte solution causing non-reproducible junction potentials. Standard Buffer Error - if the buffers used for calibration are not prepared or stored properly the calibration will not be accurate and thus cause errors.

pH = -log [H+]

Glass Electrode

The above equation is the operational definition of pH as defined by the National Institute Standards and Technology. pHu and pHs are the pH values for the solution of interest and the standard solution, respectively. Eu and Es are the cell potentials. T is the temperature in Kelvin.

How to Care for Electrode:- Store in proper storage solution (not dry)- Rinse with DI water after each use- Has a life span that should be observed- If the electrode is not properly taken care of the life span will be deminished

Demonstration of 3 point calibration

Calibration~ Can calibrate most meters to 5 points ~ Should always calibrate for the range of measures going to be taken. (ex, calibrate at pH's 4 and 7 if most readings will be around 5)~ meters should be calibrated every day if they are being used everyday. otherwise just before they are used. if they are used continously for over 8 hours they should be calibrated every 8 hours.

Manual for pH MeterSkim through whole document, look specifically at pages 48-54.

Refences that aren't linked:- Principles of Instrumental Analysis, Skoog, D. A., et al. (5th ed.) Saunders College, 1998.-

Calibration Curve


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