AP Chem Electrochemistry

Write the FULL equation for Q

(product)^(product's stoichiometric #)/(reactant)^(reactant's stoichiometric #)

What kind of reaction happens in an electrolysis cell?

A "non-spontaneous reaction"

What kind of reaction happens in an battery cell?

A "spontaneous reaction"

For this reaction: AlF6 3− + 3 e− = Al + 6F− Which of the following occurs in the reaction? (A) AlF6 3− is reduced at the cathode. (B) Al is oxidized at the anode. (C) Aluminum is converted from the −3 oxidation state to the 0 oxidation state. (D) F− acts as a reducing agent. (E) F− is reduced at the cathode.

A; once we identity that F is a spectator ion, we can figure out that D and E are both wrong, B and C suggest that Al is being oxidized but it should be obvious that this is a reduction, therefore A is the only one that can be correct

If a copper sample containing some zinc impurity is to be purified by electrolysis, the anode and the cathode must contain which of these? (A) Anode - Pure copper Cathode -Pure zinc (B) Anode - Pure zinc Cathode - Pure copper (C) Anode - Pure copper Cathode - Impure copper sample (D) Anode - Impure copper sample Cathode - Pure copper (E) Anode - Impure copper sample Cathode - Pure zinc

Anode - Impure copper sample Cathode - Pure copper A few steps here - 1. Identify that Copper is getting oxidized because it has the higher reduction potential so in an electrolysis cell must be reversed 2. Considering that, the copper we wish to remove must be at the anode. That creates copper ions 3. In order for the copper to be purified those Copper ions must then bond to pure copper to create a pure sample, thus the answer must be D ( long ass explanation - You have a piece of copper metal, mostly copper but with a small amount of Zn in it, and you want to purify it so the copper is by itself and the Zn is not in it. The problem calls that the impure copper. Here is what we want to happen. We want the Cu/Zn in the impure copper/zinc rod or bar to go into solution as this. Cu ==> Cu+2 + 2 electrons Zn ==> Zn^2 + 2 electrons. So one electrode will be the impure piece of Cu/Zn we have been given. At the other electrode, we want the Cu^+2, now in solution form, to plate out. What will we plate it out on. A thin strip of copper metal (in the problem called pure copper), of course. And the electrolysis cell will have insufficient voltage to plate out the Zn^+2, now in solution, so it will stay in solution. That eliminates answers a, b, and e since we aren't trying to purify Zn. We want impure Cu/Zn to go into solution at one electrode and for the copper ions then in solution to plate out at the other electrode. If we want + charged Cu^+2 ions to plate out, they will be attracted to the negatively charged electrode of the cell, the cathode in an electrolytic cell; therefore, we place a thin strip of pure copper for the cathode. That means we place our impure Cu/Zn metal bar (or whatever shape it has) as the anode at the positively charged electrode. That makes d the correct choice.)

63. Which of the following expressions is correct for the maximum mass of copper, in grams, that cou1d be plated out by electrolyzing aqueous CuCl2 for 16 hours at a constant current of 3.0 amperes? (1 faraday = 96,500 coulombs) (A) [(16)(3,600)(3.0)(63.55)(2)] / (96,500) (B) [(16)(3,600)(3.0)(63.55)] / [(96,500)(2)] (C) [(16)(3,600)(3.0)(63.55)] / (96,500) (D) [(16)(60)(3.0)(96,500)(2)] / (63.55) (E) [(16)(60)(3.0)(96,500)] / [(63.55)(2)]

B; (explanation - 16*3600 is time, since time goes into the equation for coulumbs it must be at the top 3.0 is for amps, it goes into calculating charge in coulumbs so it goes at the top 63.55 is the molar mass of copper, since we are trying to find mass from mols we must multiply the mols of copper by mass 96500 must be at the bottom because you have to divide the coulumbs you got at the top to get faradays 2 at the bottom because although we already has Faradays, we also know that Cu requires to electrons to be reduced so half of the Faradays calculated is the mols ofC opper created)

Why is the salt bridge usually made out of ionic compounds with K in it?

Because K is soluble therefore it won't form a precipitate.

Why is E negative in an electrolysis cell?

Because instead of generating Voltage it uses Voltage (and thus requires a battery)

Zn(s) + Cu2+ = Zn2+ + Cu(s) An electrolytic cell based on the reaction represented above was constructed from zinc and copper half-cells. The observed voltage was found to be 1.00 volt instead of the standard cell potential, E°, of 1.10 volts. Which of the following could correctly account for this observation? (A) The copper electrode was larger than the zinc electrode. (B) The Zn2+ electrolyte was Zn(NO3)2, while the Cu2+ electrolyte was CuSO4. (C) The Zn2+ solution was more concentrated than the Cu2+ solution. (D) The solutions in the half-cells had different volumes. (E) The salt bridge contained KCl as the electrolyte.

C; because Zn2+ is the ion that is created, also known as the product, by increasing Zn2+ you increase the amount of products and thus you increase Q. According to the nernst equation, the observed/real voltage goes down as Q increases, thus the cell potential is lowered.

What is the full Nernst equation when K is 298?

Ecell = Estatic - (0.0592/n)log(Q)

What happens to the voltage of the cell when you remove the salt bridge?

It goes to 0 quickly because the redox reaction evens it out and without the salt bridge the ions don't get replenished so the reaction stops taking place.

If a reversible reaction goes one way in a battery cell will it go the same way or the opposite way in an electrolysis cell?

It will go the opposite way.

In an electrolysis cell that allows for current to run through it what is true of K, E, and G?

K<1, G>0, E<0

Referring to Q = lt a) What is Q? b) What is l? c) What is t?

a) Q is charge in coulumbs b) l is charge in amps c) t is time in seconds

a) What is a concentration cell? b) What is required for a concentration cell to have voltage? c) Is the below a legitimate cell equation? Why? Cu 2+ (2 Molar) | Cu || Cu | Cu 2+ (0.5 Molar)

a) when the anode and the cathod are made of the same substance and the ions they placed into the same type of ions b) the different flasks must have different Molarity of substances c) Yes; because the Molarity of the Reactants are Higher than that of the product therefore Q is higher and thus the reaction can take place as per the Nernst Equation