Question 25

[admin]

By definition, the anode is where current flows in meaning it is positively charged (anions are actracted to anodes).

Ref:
http://www.av8n.com/physics/anode-cathode.htm
http://www.pcmag.com/encyclopedia_term/0,2542,t=anode&i=37785,00.asp

In the Figure given in this problem, you can clearly see that the larger terminal of the battery (the positive terminal) is on the left meaning that current will flow to the electrode on the left = anode. The solution is irrelevant.

Anode in an electrolytic cell:
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch20/faraday.php

[admin]

The concept that the question is testing is as follows: before getting bogged down in any details, you first assess the diagram. There is a battery. The rule for batteries is that the larger terminal is always positive and the smaller terminal is always negative. Normally that would be the only thing that you would need to memorize regarding this problem but even that is given.

Because the terminal on the left is positive and it is connected by wire to the electrode on the left, A, then means that A has now become positive. Because A is positive, no matter what is in solution, if anything is negative, it will be attracted to A.

On to your other question: is the anode always positive? No, but it is always positive in electrolytic cells (which is the one in this question; driven by a battery). It is negative in a galvanic cell.

Ref: http://en.wikipedia.org/wiki/Anode

[admin]

This is very straightforward: electrolytic and galvanic (electrochemical) cells are opposites. Electrolytic cells require energy so you will see it hooked up to a battery. Galvanic cells ARE batteries! They spontaneously create energy (positive net Eo values).

[admin]

The discussion from that link underlines the fundamentals which was discussed above and in the Explanation to this problem but then it does discuss some specifics and perspectives that are beyond what you need for the MCAT. I have not comment on those perspectives including the example that you mentioned.

[admin]

Bump.