Science Buddies: "Ask an Expert"

I'm planning on doing a project related to voltaic cells and I'm confused about how a salt bridge works in a cell. I know that it is meant to maintain charge neutrality in the two half-cells. Some sources say that only the ions in the salt bridge flow into each half-cell to balance charge, others say that both the ions in the salt bridge and the ions in each half-cell solution flow into each half-cell to balance charge, and others say that only the anions in the cathode flow through the salt bridge to the anode. Which is the correct explanation?

Hi,

The role of a salt bridge is to provide a conducting path for ions to move between electrodes in both directions. All charged ions in the path of the voltage gradient move, though the velocity of each ion depends both on the ion, its charge, and the electric field strength. If the ion is colored, its motion can be measured. See:

http://www.science.com.tw/catelog/image ... C06_03.pdf

I believe all your alternative statements could be correct depending on the length of the salt bridge, the voltage drop across the cell, and the length of time the voltage is applied. You may want to do some research on transference numbers and the Hittorf experiment, a method of measuring ion migration by titration following electrolysis

http://tsascience.com.au/images/pdf/LEC/LEC06_04.pdf

You may be interested in this book:

http://books.google.com/books?id=iDPCwb ... ty&f=false

This is a fascinating subject area - have fun with it!

Best regards,

Barrett L Tomlinson

thanks!