Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Ions conduct electricity

  1. Aug 19, 2011 #1
    Hello, in water NaCl break itself into positive and negative ions but i didn't understood how exactly works the electricity conductions... the negative ions go to positive so seen that they are negative shouldn't repel the flow of electricity causing no conduction?

  2. jcsd
  3. Aug 19, 2011 #2
    I think

    The negative ions go to the positive and give up electrons while at the same time the positive ions go to the negative and steal electrons. So from the point of view of the potential loop the circuit is completed.
  4. Aug 19, 2011 #3
    but all is done only by ions, so where are the electrons of electric flow?
  5. Aug 19, 2011 #4


    User Avatar

    Staff: Mentor

    Any stream of charged particles means flowing current. After all

    [tex]I = \frac Q t[/tex]
  6. Aug 19, 2011 #5
    The electrons flow along the conductor that is inserted into the water to get closer to the positive ions, those electrons are fed to the conductor from the negative ions at the other end of the loop or from any other source like a wall outlet.
  7. Sep 22, 2011 #6
    You mean like positive ions "charge" themself with the electrons of the flow ond "discharge" them at the positive point?
  8. Sep 22, 2011 #7


    User Avatar

    Staff: Mentor

    What happens at the electrodes is separate from the current flowing in the bulk of the solution. But you are right that some kind of reaction is needed on electrodes for the charge transfer - these are always redox reactions.
  9. Sep 23, 2011 #8
    I think that this thread doesn't belong here. It must be moved to chemistry section.

    Anyways, coming back to the question. Hii Scientifico !! Always remember that salts conduct electricity when they are in aqueous solution or in fused/molten state. NaCl is dissociated in aqueous solution into Na+ and Cl- ions. Electricity is conducted by movement of ions , yes there is mass movement and loss of energy too unlike metallic conductors. Let us assume that cathode and anode both are made of Graphite. If we consider water as aqeous solution then H2O <---->H+ + OH-. Here Na+ and Cl- ions are attracted to respective electrodes rather than H+ and OH- because :
    1. We are taking concentrated NaCl solution. Probability of NaCl ions to be attracted to electrodes is more than H2O ions.
    2. After all Na+ has greater mass than Hydrogen so it repels H+ here and there. So is Cl- to OH-.
    (Electrification series play negligible role)

    Na+ is attracted towards cathode. It gains electrons from cathode(negative electrode) and become neutral Na and sticks to cathode. This way cathode looses electrons.
    Cl- is attracted towards anode. It looses electrons to anode(positive electrode) and become neutral Cl and is released to atmosphere as Cl2. This way anode gains electrons and these electrons flow to positive terminal of battery. This is how electricity is conducted by ions.

    As LostConjugate marks "So from the point of view of the potential loop the circuit is completed."
  10. Sep 23, 2011 #9
    In a typical ionically charged liquid, negative ions flow in one direction, positive in the other. Some may combine, some don't.

    You might find reading about electron( negative charge) and hole( positive charge) migration in semiconductors interesting....

    another version of the same effects is galvanic corrosion:


    Cathodic protection [of underwater boat metals, for example, like through hull fittings and propellers and shafts] depends on the flow of ions in salt water....without such movement of charged particles there would be virtually no protection of boat metals.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook