Lecture - 8 Indicator electrodes - Copy.pptx

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1. POTENTIOMETRY (Different types of Electrodes) Lecture - 8 Subject – Pharmaceutical Analysis-I Course – B. Pharm 1 st Year Faculty Name – Umesh Kumar

2. Unit- V

3. Contents Indicator Electrodes Metal indicator electrodes Electrodes of the first kind Electrodes of the second kind Electrodes of the third kind Redox indicator electrode

4. 1. Indicator Electrode This electrode measures potential when connected to a suitable reference electrode. An electrode which is used to measure potential or pH of a solution is called an indicator electrode. Metallic electrodes and glass electrodes are major types of indicator electrodes.

5. A. Metal electrodes Metal electrodes are available in following categories- Electrodes of FIRST kind Electrodes of SECOND kind Electrodes of THIRD kind Metallic redox electrodes.

6. 1. Electrodes of FIRST kind The electrodes in this category are reversible with respect to their metal ions. For example a metal rod or wire in contact with a solution of its own ions; silver rod dipped into silver nitrate solution. The half reaction is- Ag+ + e- = Ag According to Nernst equation E = 0.799 – 0.0591 log1/Ag+

7. 2. Electrodes of SECOND kind These are a kind with two interfaces such as metal rod coated with a thin layer of its sparingly soluble salt. The reaction involved on its surface. This category will include silver coated with a thin deposit of silver chloride or mercury with mercurous chloride. Electrode of this type can be used for direct determination of the activity of metal ion or the anion used in coating (for e.g. chloride ion in silver chloride).

8. Conti…….. Silver can serve as an electrode of the second kind for halide and halide like anions; Silver Silver chloride electrode. Ag I AgCl (s) I Cl - The half cell reaction is- AgCl (s) + e- Ag (s) + Cl - , Eo = 0 The potential will be, Ein = 0.22 – 0.0591 log a Cl -

9. Electrodes of THIRD kind This category includes; a small mercury electrode with gold amalgamated wire in contact with solutions containing metal ions to be titrated by echelon such as EDTA.

10. Redox indicator electrodes; In Redox electrodes an inert metal is in contact with or solution containing the soluble oxidized and reduced forms of the redox half reaction. The inert metal used is generally platinum. The potential of such inert electrode is determined by the ratio of the reduced and oxidized species in the half reaction.

11. Glass Electrodes To be continued in Next video