pH meter in detail with better way of understanding

1. PH Meter
Stephen C Pramod
Asst Prof., Dept of EIE,
CVR College of Engineering,
Vasthunagar, Mangalpalli,
Ibrahimpatnam, Hyderabad – 501510
Ph:9885819803, Mail ID: pramod.kumar@cvr.ac.in

3. PH Meter
Principle
pH is defined as the negative logarithm of hydrogen ion concentration.
pH= -log [ H+ ]
p = power
H = hydrogen
[H+ ] = hydrogen ion concentration
The pH of a solution can be measured by the pH meter. The glass
electrode is an half cell and the calomel electrode is another half cell.

8. Electrodes and Potentiometry
Reference Electrodes
2.) Silver-Silver Chloride Reference Electrode
 Convenient
- Common problem is porous plug becomes clogged
Eo
= +0.222 V
Activity of Cl-
not 1E(sat,KCl) = +0.197 V

9. 0

10. Electrodes and Potentiometry
Reference Electrodes
3.) Saturated Calomel Reference Electrode (S.C.E)
 Saturated KCl maintains constant [Cl-
] even with
some evaporation
 Standard hydrogen electrodes are cumbersome
- Requires H2 gas and freshly prepared Pt surface
Eo
= +0.268 V
Activity of Cl-
not 1E(sat,KCl) = +0.241 V

11. Electrodes and Potentiometry
pH Electrodes
1.) pH Measurement with a Glass Electrode
 Glass electrode is most common ion-selective electrode
 Combination electrode incorporates both glass and reference
electrode in one body
Ag(s)|AgCl(s)|Cl-
(aq)||H+
(aq,outside) H+
(aq,inside),Cl-
(aq)|AgCl(s)|Ag(s)
Outer reference
electrode
[H+
] outside
(analyte solution)
[H+
] inside Inner reference
electrode
Glass membrane
Selectively binds H+
Electric potential is generated by [H+
] difference across glass membrane

12. Electrodes and Potentiometry
pH Electrodes
1.) pH Measurement with a Glass Electrode
 Glass electrode is most common ion-selective electrode
 Combination electrode incorporates both glass and reference
electrode in one body
Ag(s)|AgCl(s)|Cl-
(aq)||H+
(aq,outside) H+
(aq,inside),Cl-
(aq)|AgCl(s)|Ag(s)
Outer reference
electrode
[H+
] outside
(analyte solution)
[H+
] inside Inner reference
electrode
Glass membrane
Selectively binds H+
Electric potential is generated by [H+
] difference across glass membrane

13. Following reactions take place in the electrodes
● The glass electrode contains Ag, AgCl, and HCL. All these remain in the
ionized state.
Ag <—————> Ag+ + e–
AgCl <—————> Ag+ + Cl-
HCL <—————> H+ + Cl–
All the above three equilibrium reactions are balanced. In the glass electrode, H+
is generated.
● The calomel electrode contains Hg, Hg2Cl2 , and KCL.
Here also the following series of ionizations take place.
Hg <————> Hg+ + e-
Hg2Cl2 <————> 2Hg+ + 2Cl-
KCL <————> K+ + Cl-
The above equilibrium reactions are balanced. In the calomel electrode, H+ is not
generated.

19. Different pH values

21. Applications of pH meter
● For the diagnosis of various disorders in human
body
● Agriculture
● Brewing
● Corrosion Prevention
● Dyeing
● Jam and Jelly Manufacturing
● Printing
● Pharmaceuticals