Electrochemistry Flashcards
True or false: Galvanic cells always involve spontaneous reactions with a positive potential difference overall, and reduction occurring at the anode.
This statement is false. Though the first portion of this statement is correct, oxidation always occurs at the anode and reduction always occurs at the cathode, no matter the cell type.
What kind of cell is a concentration cell?
Galvonic/Electrolitic
True or False: In a glavonic cell, the reduction potential must be positive
true
True or False: Positive reduction potentials are associated with spontaneous reactions
True
Where does oxidation occur in an electrochemical cell?
Oxidation occurs at the anode
Where does reduction occur in an electrochemical cell?
Reduction occurs at the cathode
Why is a salt bridge necessary in a glavanic cell?
As the anode is oxidized, it is losing electrons and loses mass along with it. If there was no bridge, the cathode/solution would build up a negative charge which would hinder the reaction. The bridge serves to prevent this build up.
True or False: Galvanic cells are always spntenous
True
What is the sign of the anode in a galvanic cell?
Negative anode
What is the sign of the cathode in a galvanic cell?
Positive
What is the sign of the reduction potential of a galvanic cells?
Postive
How do you calculate the number of moles of metal deposited onto the cathode in electroplating?
mol=I(t)/n(F) I=current t=time n=number of moles needed to reduce ion to elemental state F= farraday’s constant (1x10^5 C/mol)
True or False: In galvanic cells, electrons flow from anode to cathode and in electrolytic it is the opposite
False, they flow anode to cathode regardless of the type of cell you have
An electrolytic cell has zinc solid in a zinc sulfate solution which is used for electroplating. A current of 50 amperes runs through the solution for 20 minutes. How many moles of zinc are plated out?
Since 50 amps is the same as 50 coulombs per second, we can do the following stoichiometry: (50 coulombs / 1 second) x (60 seconds / 1 minute) x (20 minutes) x (1 mol e- / 96,485 coulombs) x (1 mol Zn / 2 mol e-) Rounding Faraday’s constant to 100,000 coulombs/mol e- and completing the calculations, we get 0.3 moles of Zinc
The standard reduction potential of NiO2 is +0.49 V and the standard reduction potential of Cd(OH)2 is -0.81 V. In the reaction below, is the battery discharging or recharging? Why? Cd + NiO2 + 2H2O → Cd(OH)2 + Ni(OH)2
Discharging because the overallEcell is positive
While the Nernst equation can be written in a variety of ways, one particularly biologically relevant iteration is shown below:
Here, Vm represents the equilibrium membrane potential (in mV) for a particular ion, while z represents the valence of that ion. In neurons, the overall equilibrium potential is determined almost solely by potassium cations. Which set of conditions will yield a membrane potential closest to its actual resting value in humans?
A.[K+outside] = 10 mM; [K+inside] = 149 mM
B.[K+outside] = 149 mM; [K+inside] = 10 mM
C [K+outside] = 13 mM; [K+inside] = 100 mM
D [K+outside] = 100 mM; [K+inside] = 13 mM
A.[K+outside] = 10 mM; [K+inside] = 149 mM
In humans, the resting membrane potential of a typical neuron is approximately -70 mV. For this reason, and since K+ has a valence of +1, we know that the log term in the above equation must be negative. Therefore, [K+inside] needs to be larger than [K+outside]. Furthermore, if the internal potassium concentration were exactly ten times the external [K+], the value for Vm would be -61 mV. As we are looking for a potential that is even more negative, [K+inside] must be relatively larger. Choice A displays a [K+inside] value that is around 15 times greater than [K+outside], which resembles values found in vivo.
