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CH 456_Fluoride lab(1)-2

CH 456_Fluoride lab(1)-2 - Potentiometric Determination of...

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Potentiometric Determination of Fluoride in Solutions This experiment is designed to introduce the basic operational principles and illustrate an application of ion selective electrodes (ISEs) for the determination of fluoride ion (F - ) in water. The water supplies of most cities contain fluoride, which is added to prevent tooth decay for the population as a whole. You will use a fluoride ISE connected to a simple millivolt/pH meter to record the potentials of a series of aqueous standards having known fluoride activities to generate a calibration curve as well as a standard additions curve. You will then measure the fluoride ion activity in a sample of tap water, bottled water and mouthwash to determine the amount of fluoride ion present using both the calibration and standard additions curve. Required Reading Quantitative Chemical Analysis by Daniel C. Harris 1 7 th Edition Introduction : Ch. 14 Fundamentals of Electrochemistry, Sect. 14-4 through 14-6 Theory : Ch. 15 Electrodes and Potentiometry, Sect. 15-4 through 15-7 Analysis : Ch. 4 Statistics, Sect. 4-7 through 4-9, and Ch. 5 Quality Assurance and Calibration Methods, Sect. 5-2, 5-3. 8 th Edition Introduction : Ch. 13 Fundamentals of Electrochemistry, Sect. 13-4 through 14-6 Theory : Ch. 14 Electrodes and Potentiometry, Sect. 14-4 through 14-7 Analysis : Ch. 4 Statistics, Sect. 4-7 through 4-9, and Ch. 5 Quality Assurance and Calibration Methods, Sect. 5-2, 5-3. Pre-Lab Written: Complete the calculations required for Steps 5 and 8 of the sample preparation procedure. Quiz Topics: Understand the purpose and basic procedural steps of the experiment. What methods are used to analyze results obtained? What is and ISE and what does it measure? What effect would fluctuating temperatures have on ISE measurements? Why is a buffer added to every sample before measurement?
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Background Potentiometry allows for the determination of concentration in a variety of samples over a fairly large range. Some advantages of using an ISE (ion selective elect rode) as means of analysis incude efficiency, selectivity, and lack of interference with the sample itself. In today’s lab, you will determine the amount of fluoride ion present in Austin tap water as well as bottled water and mouthwash. You will quantify the fluoride present by creating calibration curves from a supplied standard stock solution and using the standard addition method. Potential is measurement of ion activity (mV) rather than concentration. However, the ion activity is proportional to concentration when the ionic strength is held constant. This is usually accomplished in ISE experiments by adding TISAB (total ionic strength adjustment buffer). The TISAB that you will be using in this lab consists of a mixture of glacial acetic acid, concentrated NaOH, NaCl, and 1,2- diaminocyclohexanetetraacetic acid (CDTA). CDTA is a complexiometric salt which binds selectively to metal ions and keeps them from interfering with the ionic activity registered on the multimeter.
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