This document provides a summary of lecture 8 on pharmaceutical analysis which discusses different types of indicator electrodes used to measure potential or pH. It outlines metal indicator electrodes including electrodes of the first, second and third kind as well as redox indicator electrodes. Electrodes of the first kind involve a reversible metal rod in contact with its own ions. Electrodes of the second kind have two interfaces like a silver rod coated with silver chloride. Electrodes of the third kind include a mercury electrode with an amalgamated gold wire to titrate solutions. Redox indicator electrodes use an inert metal like platinum in contact with reduced and oxidized forms of a half reaction. The lecture continues in the next video.

1. Lecture- 8
Subject – Pharmaceutical Analysis-I
Course – B. Pharm 1st 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. To be continued in Next video