Problem Set 5

1. A galvanic cell maintained at 298 K is constructed using a copper electrode immersed in aqueous 2.0M CuSO₄ in one container and a nickel electrode immersed in aqueous 0.0010M NiSO₄ in the other container. The two are connected through a salt bridge

a) Write the reaction that occurs at the anode where oxidation occurs.

b) Write the reaction that occurs at the cathode where reduction occurs.

c) Write the overall electrochemical reaction that occurs.

d) Write the Q expression for this overall reaction and calculate the numerical value of Q.

e) Calculate the cell potential.

f) Calculate the equilibrium constant for this reaction.

g) Calculate the change in Gibbs Free Energy for this reaction.

2. A particular neuron had [K⁺] intracellular and extracellular concentrations of 150 mM and 5 mM respectively and a resting membrane potential of –65 mV. This cell was exposed to a G protein coupled receptor ligand that activated (opened) potassium ion channels.

a) Calculate the DG associated with the potassium concentration gradient and comment on what would be expected to occur---based only upon concentration gradients--when the potassium ion channels open.

b) Explain why it would be logical to think that ion channels permeable to potassium ions would also be permeable to sodium ions.

c) Now explain why potassium ion channels do not allow sodium ions to pass. Clearly support this in terms of underlying physical principles.

d) Calculate the change in Gibbs Free Energy required to move a mole of potassium ions into a cell across a –65 mV potential gradient if potassium ion concentrations were equal on both sides of the membrane.

e) Explain what effect (stimulatory or inhibitory) the ligands responsible for opening up potassium ion channels would have on this neuron. Clearly provide the rational for your answer to effectively explain the underlying physical basis for your prediction.

3. Problems from Chapter 20 of Kotz text: 20.21, 20.31, 20.57