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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: sgeos on May 23, 2012, 10:18:15 PM

Title: How does a galvanic cell salt bridge work?
Post by: sgeos on May 23, 2012, 10:18:15 PM

In a galvanic cell, electrons flow from the anode to the cathode.  In the process they can be harnessed to do useful things.  Half of the reduction oxidation reaction happens in each half cell.  Maybe the anode dissolves and cathode is plated.  The salt bridge is used to maintain electrical neutrality.  If I treat the salt bridge as a magical black box that just works, all of this makes sense to me.  I am, however, having trouble finding a definitive answer as to exactly how the salt bridge maintains electrical neutrality.  Is anyone familiar with the mechanism by which a salt bridge maintains electrical neutrality in a galvanic cell?

I know what a salt bridge does.  I know why it is necessary.  How does it work?  So far as I can tell, ions are released from the salt bridge into the electrolyte.  Is this correct?  One of the images on Wikipedia could lead a person to believe the salt bridge absorbs ions.  Does the chemistry of the salt bridge change as the reaction progresses?  Is a salt bridge necessarily disposable or is it reusable reusable?  Does the salt bridge change the chemistry of one or both of the half cells?  Do anions physically migrate across the salt bridge to the other half cell?  Does all of this depend the chemistry of any given cell?  What exactly is going on?

Title: Re: How does a galvanic cell salt bridge work?
Post by: Ari Ben Canaan on May 23, 2012, 11:03:58 PM

This should help :

http://www.dynamicscience.com.au/tester/solutions/chemistry/redox/redoxCuZnSALTBRIDGE.gif

Its an animation.

Title: Re: How does a galvanic cell salt bridge work?
Post by: sgeos on May 23, 2012, 11:41:23 PM

I saw that animation.  Does it depict how how salt bridges necessarily work?  The animation leads me to believe the chemistry of the half cells changes as the salt bridge seeps ions.  I.e., the salt bridge dissolves in the half cells and obviously needs to be replaced after it has been sufficiently used up.  Is this the case?

Title: Re: How does a galvanic cell salt bridge work?
Post by: Borek on May 24, 2012, 03:29:00 AM

Yes, salt bridges have a limited life span - they loose their ions to the half cells solutions. We usually select ions in salt bridges in such a way they are inert for the researched process, so their presence can be ignored.

Title: Re: How does a galvanic cell salt bridge work?
Post by: sgeos on May 24, 2012, 05:09:21 AM

Thank you for all the help.  I think I now have a solid intuitive understanding of salt bridges.