Conductivity (Specific Conductance)

November 29, 2016 3:25 pm

Conductivity is the ability of the water to pass electricity through it.

Definition

Conductivity is defined as the ability of the sample to conduct or transmit heat, electricity or sound through it. Its units are Siemens per meter (S/m) and millimhos per centimeter [mmho/cm]. Its symbol is k or s.

Range

Sample Handling & Preservation

Collect the laboratory Sample in a polyethylene bottle completely filled and tightly stoppered. Soda glass bottles shall not be used. Measurement of conductivity should be performed as soon as practicable, particularly when there is a possibility of an exchange of gases such as carbon dioxide or ammonia with the atmosphere, or a possibility of biological activity. Biological activity can be reduced by storing the samples in the dark at 4⁰C; however, samples shall be brought to equilibrium at the reference temperature of 25⁰C before the conductivity is measured. No suitable preservative is known for samples taken for conductivity measurements.

Analysis Procedure: [ IS 3025-14 (1984) ]

• Prepare the equipment for use as instructed by the manufacturer and ensure that an electrode cell of known cell constant appropriate to the desired measuring range is fitted. The test Portion depends on the equipment used.
• If the cell constant is not accurately known, determine the constant using the potassium chloride Standard solutions appropriate to each desired measuring range. Check the cell constant at least once every 6 months.
• Many instruments incorporate cell constant correction as an integral function and thus a direct reading of electrical conductivity is obtained.
• Otherwise multiply the conductance value obtained by the cell constant to obtain electrical conductivity.
• For high precision work, carry out the measurement of electrical conductivity when the sample and apparatus in direct contact with it has attained equilibrium at 25, 0 + 0.1⁰C. Thus all sources of error that may arise from the use of temperature compensators, or from mathematical correction techniques, are eliminated.

Factors affecting conductivity

Concentration of ions

As the concentration of ions in the solution increases, conductivity increases.

Temperature

Conductivity of the solution increases with the increase in temperature.

Effect of salt type

The conductivity of different salts vary widely and is determined by the factors such as size of the ions, number of ions, and the charge density on these particles in the solution.

Interferences

• The measured values of the electrical conductivity can be affected by contamination of the sample within the cell. The presence of gross suspended matter, grease or oil can cause fouling of the electrodes.
• Interferences caused by such effects are not, in routine operation, easily recognized. They may cause a change in cell constant, but this can only be ascertained by checking with the appropriate potassium chloride Standard Solution.
• Interference may result from air bubbles collecting on the electrodes when warming the Sample to 25^oC.
• Measurements of waters with electrical conductivities less than 1 mS/m are influenced by atmospheric carbon dioxide and ammonia. In these cases measurement shall be carried out in flow type equipment. When dealing with water of very low ion content the contribution of the electrical conductivity of highly pure water may be significant.

Conclusion

This experiment helps to determine the conductivity of the water sample which helps to determine the quality of water

Disclaimer

The details given are for general understanding. References should be taken from respective authorized agencies.