Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Foobarz on March 15, 2012, 07:02:16 PM
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Both in a galvanic cell and an electrolytic cell, how do you determine if the anode is positive or negative?
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Here are some notes that might help you out,
-An ion with more electrons than protons is negatively charged and is called anions hence why anode is the negatively charged electrode
-The two electrodes in an electrochemical cell can be either an anode or a cathode. An anode is the electrode where the electrons leave the cell and oxidisation occurs. A cathode is the opposite; it’s where the electrons enter the cell and reduction occurs. Its dependant on the reactivity of the electrodes to whether it becomes an anode or a cathode, most reactive = most reductant= cathode. In chemistry the cathode is a positive terminal as it gains negatively charged electrons and the anode is the positive terminal where it disperses its electrons. If it is in between it is called a bipolar where it functions as one anode cell and one cathode cell.
-Oxidation occurs to the anode where it loses its electrons
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Which way do the electrons flow? (i.e. from anode to cathode or vice-versa?)
What would electrons be attracted to? The positive electrode or the negative electrode?
With those questions in mind, the answer should be obvious.
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Ok so if electrons flow from anode to cathode, then the cathode is positive since it attracts negative electrons.
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^Is the above true?
Whichever electrode the electrons flow to, that electrode is the positive one (eg the cathode since that is where reduction occurs).
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This is a little trite, but I always remembered the cathode as the positive one (+), because cathode contains the letter 't'. Its far better for everyone to do what you've all done here, and think about reduction.oxidation and electrons released/acquired 'tho. My little trick just comes in handy when you're reading something that say attach cathode and you want to check you've wired it right before you turn on the juice.
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("AAA"): "Anode Attracts Anions" (i.e. it is positively charged).
this works for everything except for a galvanic cell (a battery), where the naming is reversed.
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In any electrochemical or electrolysis cell
Current enters through the anode.
Current exits through cathode.
(A) Anode Cathode (C)
(O) Oxidize Reduce (R)
It is alphabetical!
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^I know that, but is the following true?
In galvanic cell, anode is negative, cathode is positive.
In electrolytic cell, the anode (place of oxidation) is attached to the positive end of the battery, and the cathode (place of reduction) is attached to the negative end of the battery?
^I got the electrolytic cell info myself when I did the electrolysis of water lab with a 9 volt battery, since my book (Chang, 5th ed.) only explains anode and cathode and doesnt talk about the positive and negative signs at all.
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^I know that, but is the following true?
In galvanic cell, anode is negative, cathode is positive.
In electrolytic cell, the anode (place of oxidation) is attached to the positive end of the battery, and the cathode (place of reduction) is attached to the negative end of the battery?
^I got the electrolytic cell info myself when I did the electrolysis of water lab with a 9 volt battery, since my book (Chang, 5th ed.) only explains anode and cathode and doesnt talk about the positive and negative signs at all.
Read what I posted carefully:
("AAA"): "Anode Attracts Anions" (i.e. it is positively charged).
this works for everything except for a galvanic cell (a battery), where the naming is reversed.
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Oh ok thanks! Pradeep's is good, but CH, your explanation is clearer.
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Oh wait one more question:
The wikipedia article on anode says this: "It is continued internally by positive ions flowing into the electrolyte from the anode, i.e., away (surprisingly) from the more negative electrode and towards the more positive one (chemical energy is responsible for this "uphill" motion)."
Why DO cations flow AWAY from the anode if the anode is negatively charged? (I don't really understand the chemical energy part).
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