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Electrical Conductivity of Fluids

  1. Jan 20, 2009 #1
    So it has always been my understanding that in order for something to electrically conductive it has to have more electrons than it needs. If the electrons can be easily shaken from their atoms, then it's conductive. The easier it is for the electron to move to the next atom the more conductive it is correct?

    So then when trying to make a solution conductive it would be best to add negative ions correct? These negatively charged ions have a more "spare" electrons. Positive ions would make very bad conductors as they have more protons than electrons there for they don't have any "spare" or electrons that are in a higher orbit and easier to break loose. Am I wrong in my thinking?

    So then for example, when adding salt to water, NaCl, as it becomes Na+ and Cl-, it's actually the Cl- that makes it more conductive? If you could remove the sodium ions, Na+, would it become even more conductive?

    Recently in a biology text I read it mentioned how Na+, K+, Ca+ and others help increase the electrical conductivity in the body and are used in transmitting neurons. I'm not sure if there is just a different process going on in the body, involving active transportation and potentials and other things, or do positively charged ions really increase conductivity too?

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  3. Jan 21, 2009 #2


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    In NaCl, both Na+ and Cl- contribute to the electrical conductivity. The Na+ moves to the negative electrode and the Cl- moves to the positive electrode. Movement of negative charge in one direction is "effectively" the same current as positive charge moving in the opposite direction. The most important thing is that the charges are not stuck to specific locations, but are free to move.
  4. Jan 21, 2009 #3


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    Yes. A much better criterion for conductivity would be the presence of mobile charge carriers.
  5. Jan 21, 2009 #4


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    In general you are right, but this statement needs IMHO clarification.

    Not the charges are free to move, but ions. Charge moves together with ion. "Charges are not stuck" can be (wrongly) understood as free electrons moving in the liquid. That's not the case.

    Well, in some solutions that can be the case, but in the presence of water solvated electrons are about as common as kangaroos in Alaska.
  6. Jan 21, 2009 #5
    The electrical activity of neurons is completely different than what goes on in man made machines and electronics. Very briefly, when a neuron "fires" positive charges move from outside the neuron to inside the neuron. There is no flow of electrons along a conductor.

    This site has some animation that illustrates this:

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