Understanding Galvanic Cells: Salt Bridge, Electrode Potential, and More

[Misr]

hi ,world

1-What is the importance of salt bridge?


According to my textbook :
1-connects between the two solutions without allowing a direct contact between them
So what is the problem of direct contact?

2-Neutralizes the charges which are formed in the solution of two half cells as a result of red-ox reactions in the zinc and copper half cells.
OK ,that doesn't make any sense

Still don't understand the function of salt bridge.

2- Why do we put salt in the salt bridge and why shouldn't its ions react with the ions present in the two half cells?

3-Sometimes the anode is negative like in galvanic cell,so I want a general definition for the anode in any cell.

4-What is meant by electrode potential?can you help me understand the concept of electric potential and potential difference because we always learn these stuff in a terrible way and i think they are very hard to understand.

5-Electromotive series "the arrangement of the standard potentials of the elements in a descending way with respect to the negative reduction potentials and ascending relative to the positive reduction potentials"

Oh I'm very confused about this.
does this mean "oxidation potential"?
thanks in advance.

 

[Misr]

hi.there?
is there any problem with my Q?

 

[ehild]

A half-cell means a metal immersed into a solution of its own salt. There is a potential difference between the electrode and the electrolyte. http://en.wikipedia./wiki/Absolute_electrode_potential . That potential difference can not be directly measured, but only with respect to a standard electrode. The half cells are connected with a salt bridge to ensure electric contact between them. Direct contact between the half cells would mean that the two electrolytes can mix. A salt bridge (http://en.wikipedia.org/wiki/Salt_bridge) can be an U-shaped glass tube containing an electrolyte usually gelified with agar. The ions of the electrolyte take part in the electric conduction, but the gel prevents mixing with the electrolytes of the individual half cells.

ehild

 

[Misr]

what is agar? can u show me an illustration for the movement of ions through a salt bridge because can't really imagine anything from this

Thanks very much.

 

[ehild]

Agar or afar-agar is a kind of jelly. http://en.wikipedia.org/wiki/Agar It is solid enough to stay inside the U-tube but also humid enough so the ions can migrate in it.

As for motion of ions see the attached picture of a zinc-copper cell and read my very much simplified explanation.
Zinc gives off electrons more readily than copper does. So the zinc electrode is more negative with respect to the fluid it is immersed in than the copper electrode is. There will be excess positive (zinc ) ions in the electrolyte around the zinc electrode, and excess negative (sulfate) ions in the electrolyte around the copper electrode. The jelly is neutral, contains equal amount of both positive and negative ions. The negative ions will migrate towards the zinc cell as the positive zinc ions exert some attractive force on them, and the positive ions migrate towards the copper cell. This means some current flowing through the salt bridge. The positive and negative ions neutralize with the opposite ions of the salt bridge, the electrolytes lose charge therefore the excess electrons accumulated on the zinc electrode can flow across the outer circuit through the meter to the other (positive) electrode. You get a closed circuit.

ehild

ehild