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Factors Affecting Conductivity of Electrolytes


Q. Dear sir,

I would like to know what are the factors affecting the conductivity of electrolytes.

Please do reply,

Nina Rdeleted
- Dubai, UAE


 

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.

Bassel T deleted
- Cairo, Egypt


May 10, 2008

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.

Chap Degiens
- Houston, Texas



How do concentration and temperature affect the resistance of a solution?

++

Q. I have carried out an experiment investigating how temperature and concentration of a solution affects its resistance. The solution I used was sodium Chloride, ranging temperatures between 0 °C andn80 °C and concentrations between 1.5 M and 0 M. My results appear to show a relationship of:

- Resistance is proportional to 1/concentration
- Resistance is proportional to 1/(temperature^0.5)

This is only apparent and I am not sure it is correct. I obtained these relationships by creating various graphs of resistance against some function or the other two factors. However, I am not entirely sure that this is correct. Having looked everywhere I have so far been unable to find another experiment like this to compare my results against.

Does anyone know of the actual relationship between resistance and concentration and resistance and temperature of a solution? Thank you in advance for any replies.

Robert Warwood
- England


+++

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.

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


+++

thumbsup2Trevor, again I like reading your responses.

Jon Quirt
- Fridley, Minnesota


+++

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

Most libraries have a copy,

James Watts
- Navarre, Florida

CRC Handbook of Chemistry
and Physics, 90th Edition


+++

thumbsup2Thank you very much for your replies.

Having looked at my results closely, there is no need to square root the temperature value, hence resistance is inversely proportional to temperature (or conductance is directly proportional to temperature.)

As for concentration, that still appears to be inversely proportional to resistance. However, my graphs aren't an exact science so are probably slightly wrong.

Where you say resistance is proportional to 1/c**(1/2) does that mean resistance is proportional to 1/the square root of the concentration?

I'm not clear on the way it has been written, must be a regional dialect of some kind ;-), or it means something completely different :S.

Thanks again for your replies, I'll try and make a trip to the Birmingham library today.

Robert Warwood
- England


+++

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 :-)

Bill Reynolds
   consultant metallurgist
Ballarat, Victoria, Australia

It is this website's profoundly sad
duty to relate the news that Bill
passed away on Jan. 29, 2010.



+++

thumbsup2Bill, 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

February 14, 2010

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,

Daniel Montañés, Chemical Engineer
- Buenos Aires, Argentina



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