[Chemistry] Membrane Potential

In summary: The reason for this is because the reaction proceeds to reach equilibrium, and the concentrations of the reactants and products change.
  • #1
jkh4
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[Chemistry] Another electrochemistry question

Homework Statement



Given the following half-reactions:
Ce4+ + e− → Ce3+ E° = 1.72 V
Fe3+ + e− → Fe2+ E° = 0.771 V

A solution is prepared by mixing 7.0 mL of 0.30 M Fe2+ with 8.0 mL of 0.12 M Ce4+.

Calculate [Ce4+] in the solution.

I've got the potential of a platinum electrode dipped into the resulting, equilibrated, solution (relative to SHE) to be 0.767 V, and keq of 1.1×10^16 from this equation: Ce4+ + Fe2+ ⇌ Ce3+ + Fe3+.

How do you get [Ce4+]? Why isn't that the same as the concentration posted in the question?

Thanks!
 
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  • #2
Homework EquationsKeq = [Ce3+] [Fe2+] / [Ce4+] [Fe3+]The Attempt at a SolutionYou can calculate the [Ce4+] using the equilibrium constant expression. Keq = [Ce3+] [Fe2+] / [Ce4+] [Fe3+]The concentration of Ce3+ and Fe3+ are both 0 M initially, so we can simplify this expression to:Keq = [Fe2+] / [Ce4+] Rearranging for [Ce4+], we get: [Ce4+] = [Fe2+] / KeqFrom the problem statement, we know that [Fe2+] = 0.30 M. Substituting this into the equation, we get:[Ce4+] = 0.30 M / 1.1 x 10^16[Ce4+] = 2.7 x 10^-17 MThis is the concentration of Ce4+ in the solution after it has been equilibrated. This is not the same as the initial concentration of Ce4+ (0.12 M) in the solution before it was equilibrated, which is given in the problem statement.
 
  • #3


I would like to address the chemistry involved in this question. The membrane potential, also known as the transmembrane potential, is the difference in electrical potential between the inside and outside of a cell or membrane. It is an important concept in electrochemistry, as it plays a crucial role in many biological processes such as nerve impulses and muscle contractions.

In regards to the given half-reactions, it is important to note that the standard reduction potentials (E°) are measured at standard conditions, which may not necessarily reflect the actual potential in a given solution. This is because the concentrations of the reactants and products can have a significant effect on the overall potential.

In this case, when the two solutions of Fe2+ and Ce4+ are mixed, a redox reaction occurs, resulting in the formation of Fe3+ and Ce3+. This reaction will continue until equilibrium is reached, and the resulting potential of the solution is 0.767 V. This potential is a result of the concentrations of Fe2+ and Ce4+ in the solution, as well as the Keq value of the reaction.

To calculate the concentration of Ce4+ in the solution, we can use the Nernst equation: E = E° - (RT/nF)lnQ. Here, Q represents the reaction quotient, which is equal to the concentrations of the products divided by the concentrations of the reactants. Since we know the potential (E) and the standard potential (E°), we can rearrange the equation to solve for [Ce4+].

The concentration of Ce4+ in the resulting solution will not be the same as the initial concentration given in the question because of the redox reaction that occurred. The concentration of Ce4+ has decreased due to its conversion to Ce3+ in the reaction. Therefore, to determine the final concentration, we need to use the Nernst equation.

In conclusion, the membrane potential and redox reactions are important concepts in electrochemistry and have significant implications in biological systems. The Nernst equation is a useful tool in calculating the concentrations of reactants and products in a solution and understanding the factors that influence the overall potential.
 

What is membrane potential?

Membrane potential refers to the difference in electrical charge across a cell membrane. This difference in charge is created by the movement of ions, such as sodium and potassium, across the membrane.

Why is membrane potential important?

Membrane potential is important because it allows cells to generate and maintain electrical signals, which are essential for many biological processes such as muscle contraction and nerve signaling.

How is membrane potential measured?

Membrane potential can be measured using various techniques, such as microelectrode recordings or patch clamp recordings. These methods allow for the detection of changes in electrical potential across a cell membrane.

What factors affect membrane potential?

Several factors can affect membrane potential, including the concentration of ions inside and outside the cell, the permeability of the membrane to different ions, and the activity of ion channels and pumps.

What is the role of membrane potential in action potential?

Membrane potential plays a crucial role in the generation of action potentials, which are rapid changes in electrical potential that travel along the membrane of excitable cells, such as neurons. Action potentials are triggered when the membrane potential reaches a certain threshold, causing a rapid influx of positively charged ions into the cell.

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