Conductometric Measurements and Conductance

Study Notes

Conductance and Conductometry

Specific conductance (K) is the conductance when L (length) is 1 cm and A (area) is 1 cm², or it is the conductance of a cubic centimeter of liquid (1 cm³).
Instrument used in conductometric determinations: conductance cell, oscillator (to produce AC from DC), and conductivity bridge (Kohlrausch bridge).

Applications of Conductometry

Direct conductometry:
- Used in industry for checking purity of distilled water or other chemicals.
- Used for determination of some physical constants, e.g., ionization constant.
- Calibration curve is constructed by plotting conductance against concentration.
Indirect conductometry (conductometric titrations):
- Involves measurement of conductance after successive addition of titrant.
- End point is obtained from a plot of conductance against mL of titrant.
- Advantages:
  - Can be used for determination of turbid and highly colored solutions.
  - Can be used for determination of very dilute solutions.
  - Can be used when reaction is not complete and when there is no suitable indicator, e.g., during weak acid, weak base titration.

Precautions to be Considered During Conductometric Titrations

The titrant used must be at least 10 times concentrated as the solution to be titrated.
Avoid the presence of extraneous ions, which will increase initial conductance.
The method is not suitable for detection of end point of redox reactions.

Potentiometry

Introduction: Potentiometry is a method of analysis concerned with the determination of an ion by dipping a suitable sensor in its solution (indicator electrode).
The potential of the indicator electrode is measured relative to a reference electrode possessing constant potential.
The concentration of the ion is determined using Nernst equation.

Metal Electrodes

Metals can have:
- Tendency to lose electrons and convert to its ions (high solution pressure).
- Tendency of metal ion to accept electrons and convert to element (high ionic pressure).
Examples of metals with high solution pressure: Zn°, Fe°, Co°, Ni°.
Examples of metals with high ionic pressure: Cu°, Hg°, Ag°.

Factors Affecting Conductance

Conductance has a direct relation with concentration of ions.
The size of the electrodes (dimension) affects conductance.
Conductometric measurements are usually carried out in a conductance cell, which consists of two parallel sheets of platinum as inert electrodes.

Description

This quiz covers the basics of conductometric measurements, including the instrument used and the concept of specific conductance. It explains how to measure the resistance of a solution and the role of the conductance cell and conductivity bridge.