Hi, I'm in my final year of high school doing an electrochemistry unit and there is a concept I just don't really get. I would appreciate all helps please--
Redox reaction half reactions are:
Oxidation: Zn(s) --> Zn 2+ (aq) + 2e-
Reduction: Cu2+ (aq) + 2e- ---> Cu(s)
In terms of electrodes, Zn in the anode and Cu is the cathode.
Its in a galvinic cell, Zn releases electrons to become Zn2+, but how come the anode of the galviniv cell is negatively charged? If it releases electrons, shouldn't it be Postivively charged?
Also, in terms of porous barriers to maintain electrical neutrality, why are the negative ions (anions) migrating toways the anode and the positive ions (cations) migrate towards the cathode? Shouldn't the opposites attract?
Thank you muchly for all your help!!
OK, it is a matter of definition: Where did you get the statement "In terms of electrodes, Zn is the anode and Cu is the Cathode"? That statement is correct, but it is based on the flow of current. Forget about electrons. The world long ago in physics and chemistry defined the direction of current flow as the direction of Positive charge carriers (even though in wires they don't exist). So with this DEFINTION of current flow, the definition that the anode is the terminal where current flows in fits: Zn is the place current flows in. If current is flowing inward, then it is OK for electrons to flow the opposite way.
Forget about electrons having anything to do with current flow direction.
If current (positive) is flowing in, then Zn must have a negative charge, or in physics terms, have a lower potential.
Negative ions migrate towards the Zn++ cations, which are leaving the Zn anode. See the picture here:
http://www.jiskha.com/display.cgi?id=1168798599
Another way of saying it, although Bob Pursley was eloquent, is---
By definition, the anode is where oxidation occurs.
Zn==> Zn++ + 2e
Therefore, Zn is losing electrodes and it is the anode by definition.
In electrochemistry, it is important to understand the definitions and conventions used to describe the flow of current and the behavior of ions in a galvanic cell.
Regarding the charge on the anode, the convention is based on the flow of positive charge carriers (known as current). The anode is defined as the electrode where oxidation occurs, which means it is the electrode where electrons are being released. In the case of the Zn electrode in your example, Zn is being oxidized, losing electrons to become Zn2+. So, according to the convention, the anode is negatively charged because it is the electrode where electrons are leaving.
In terms of the migration of ions, it is important to consider electrical neutrality within the cell. The movement of ions is driven by the need to maintain electrical neutrality. The positive ions (cations) migrate towards the cathode because they are attracted to the negatively charged electrode, where reduction is occurring. The negative ions (anions) migrate towards the anode because they are attracted to the positively charged electrode, where oxidation is occurring. This movement of ions helps to balance out the charges and maintain electrical neutrality within the cell.
Remember that these definitions and conventions are established for consistency and to properly describe the behavior of electrons and ions in electrochemical systems. By understanding these conventions, you can better analyze and interpret electrochemical reactions and galvanic cells.