What are the factors affecting the measurement of electrolytic conductivity using DC and AC techniques? What are the challenges and precautions related to electrolytic conductivity measurement? How to compute the cell constant?
Electrolytic Conductivity Measurement
Electrolytic conductivity measurement is a key technique used in various fields to determine the concentration of ions in an electrolytic solution. It applies a voltage to two electrodes immersed in a solution and measures the resulting current. The ability of the solution to conduct an electric current is related to its ion concentration.
DC (Direct Current) Technique
A direct current is applied across the electrodes in a DC measurement, and the resulting potential difference or current is measured. One of the main issues with DC measurement is electrode polarization, where charges build up on the electrode surfaces, resulting in a concentration gradient that can skew the measurements.
AC (Alternating Current) Technique
The AC method addresses the problem of electrode polarization by using an alternating current instead of a direct current. Because the direction of the current is continually changing, charge buildup is minimized, and more accurate conductivity measurements can be obtained.
Factors Affecting the Measurement
Challenges and Precautions
Computing the Cell Constant
The cell constant (K) is a factor used to account for the geometry of the electrode cell. It is typically determined by calibrating the cell with a solution of known conductivity. It is given by:
K = d / R
where d is the distance between the electrodes, and R is the resistance measured using a solution of known conductivity. The units of the cell constant are cm-1.
It's crucial to note that if the electrodes are not parallel plates (often in practical applications), the cell constant must be determined through calibration rather than simple geometric calculation. It's typically a good idea to periodically recalibrate the cell constant to ensure accurate measurements, as it can change over time due to factors such as electrode wear or buildup.
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