Factors Affecting Conductivity of Electrolytes

A. Conductivity of electrolytes depends on two things:
- the nature of ions in the solution and
- the type of electrode used for measuring conductivity.

As for the nature of ions, the more the ions in the solution, the higher the conductivity. The same applies for ions with larger valence. The electrode itself and the technique of measurement also affect the result.

A. Conductivity of electrolytes depends on:
- Concentration usually expressed in mg/l, at low concentrations conductivity increases with the square root of concentration.
- Type of salt in solution: NaCl, KCl, NaHCO₃ or other
- Temperature - the higher the temperature the higher the mobility of ions, hence the conductivity.

A. How refreshing it is to have a question asked where someone has actually done the experiments and wants to know if the observed answers are correct. Perhaps there are some practical budding scientists out there still!

Resistance of an electrolyte is normally referred to as its conductance and this is 1/R where R is the specific resistance. The conductance of an electrolyte is dependent on the ability of the electrolyte to carry a current and this, in turn, is dependent on the degree of dissociation of the electrolyte. The greater the dissociation, the better the conductance. To make things easier, scientists refer to the equivalent conductance of an electrolyte; this refers to the conductivity of 1 gram equivalent weight of the electrolyte. Hence the equivalent conductance of a bivalent electrolyte will be only half the molecular conductance because the "equivalent" of a bivalent system is half the "molecular". However, it has been shown by the old scientists (including Kohlrausch and Arrenhius), all of whom are long dead, that the conductance of an electrolyte (A) is dependent on the equivalent conductance at infinite dilution (a) and the concentration of the electrolyte (c) and an experimental constant (k), thus: A = a - k*c**(0.5). Hence conductance is proportional to c**(1/2); therefore resistance will be proportional to 1/c**(1/2).

As far as temperature is concerned, conductivity increases with temperature because of a combination of the increased dissociation and increased speeds of the ions. Hence resistance must be proportional to 1/T, where T is the temperature.

A. Look in the definitions and formulas section of the Handbook of Chemistry and Physics.

Most libraries have a copy,

A. Standard computer code from way back (FORTRAN, I think). * means "multiply", ** means "raise to power". More recently and in other programming languages, ^ rather than ** means "raise to power". Not a dialect, just coding from before your time :-)

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Bill, thanks for your input. I have only just picked up this thread again and missed the window. Talk about local dialect - have you heard the Birmingham accent....! Only joking - I spent many happy years there as a student.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2003

A. Hello, I can answer your question above, that about the square root of the concentration or the concentration itself in the formula. Its argument is not the salt concentration, it is the sum of the concentration of ALL ions, multiplied by its molar conductivity, as it is a more complex formula as the mentioned above.

The result of that correction in the formula is that, as the molar conductivity varies with the activity of the solution, that linear result in the formula above only works for diluted solutions... Deviations are normal if we assume that 1,5 M is not a diluted solution, and the theory is not exact! It assumes a lot of things that are not certainly correct in these conditions.

Well, I'm learning a lot of things of metal finishing here as I'm new in the business, so we'll be seeing you around! Hope my answer helps in any way.

Greetings,