- Questions
Electrolytic Cells
Hey...can u check my two answers for a and b and can u help on the rest?
8. An electrolytic cell consisting of an aqueous solution of NaCl is set up. Answer the following.
a. What is the strongest oxidizing agent present?
My answer:
Na; sodium
b. What is the strongest reducing agent present?
My answer:
Cl; chloride
c. What would you normally and incorrectly expect the cathode reaction to be?
d. What would you normally and incorrectly expect the anode reaction to be?
e. What is then the normally expected overall reaction?
f. What is the voltage required to cause this reaction?
g. What is the actual anode reaction?
h. What is the actual overall reaction?
i. What voltage is required to cause the actual reaction?
Hey...can u check my two answers for a and b and can u help on the rest?
This is not an example of the best worded set of questions I have seen; however, I will make some guesses. All of this will be wrong if I have guessed wrong. First, is this an experiment? Did you do this in the lab? Did you collect any gases at the anode and cathode? That information would be helpful. The question doesn't state how much NaCl is in the aqueous solution. If it is a moderate amount the anwers will be one thing and if it is just enough to conduct the electrical current through the cell then the answers are different. SO, I will assume, from the questions and a lot of studying and trying to figures out just what the person who wrote this wants, that the amount of NaCl is just enough to conduct and electrical current through the cell. Keep that in mind as you go through my answers below.
8. An electrolytic cell consisting of an aqueous solution of NaCl is set up. Answer the following.
a. What is the strongest oxidizing agent present?
My answer:
Na; sodium
See below.
b. What is the strongest reducing agent present?
My answer:
Cl; chloride
See below.
c. What would you normally and incorrectly expect the cathode reaction to be?
I can tell you what the reaction is, assuming my guess is right (from above) but to ask me to write the wrong reaction is----who knows. However, from the context of the other questions, I think the answer here is that the unsuspecting person might normally expect metallic Na to be plated out since sodium ions will be attracted to the cathode (the negative electrode). That won't happen. So, I think the answer wanted here is,
Na^+(aq) + e ==> Na(s)
d. What would you normally and incorrectly expect the anode reaction to be?
Again, who knows what goes here, but from the context of the entire set of questions, I think that the unsuspecting person might expect for chlorine to be given off at this electrode since chloride ions are attracted to the anode (the positive electrode). That won't happen IF we have just a enough NaCl to conduct the currect. So I think we put down that 2Cl^- ==> Cl2 + 2e. This won't happen.By the way, if we had a moderate amount of NaCl in the solution, chlorine would be eliminated here according to the above equation.
e. What is then the normally expected overall reaction?
Is this one supposed to be incorrect, TOO. I think so from the other questions listed. Therefore, if we take the incorrect answer from the cathode and add that to the incorrect answer from the anode, we will have the incorrect answer for the cell. That would be 2NaCl ==> 2Na + Cl2. This won't happen.
f. What is the voltage required to cause this reaction?
For Na + e ==> Na E = -2.74
+ 2Cl^- ==> Cl2 + 2e E = -1.36
---------------------------------
2Na + 2Cl^- ==> 2Na + Cl2 E = -4.10
Therefore, the voltage required would be greater than 4.10 volts for this incorrect reaction to occur.
g. What is the actual anode reaction?
The actual anode reaction is
2H2O ==> O2 + 4e + 4H^+
The actual cathode reaction, although not asked in this set of questions is
2H2O + 2e ==> H2 + 2OH^-
h. What is the actual overall reaction?
I will let you add the actual anode reaction to the actual cathode reaction I have in the previous question above to obtain the overall reaction. Don't forget to multiply the cathode reaction by 2 to make the electrons in the reduction half equal the electrons in the oxidation half.
i. What voltage is required to cause the actual reaction?
E for cathode reaction is about 0
E for anode reaction is about -1.23
E for the reaction is about -1.23 so you need a little more than 1.23 volts to make this reaction go.
I have ignored the issue of over voltage. I think after reading all the questions that this is trying to show that the "normally expected but incorrect answers" will require a greater voltage that you may have had and the "correct answers" require a smaller voltage that was used, perhaps in an experiment or in some experimental set up described in class or in some problem. There is a great deal of speculation here about what is actually meant so please check my work. Check my thinking. I hope this helps.
Thank u sooooooooooooo much...I get this now!