Na equil-v:
Only sodium may cross a membrane separating two compartments.
At a temperature of 28∘C, the concentrations of sodium ions are:
intracellular: 100
extracellular: 485
What is the equilibrium potential?
Give a numeric answer within 1%, in mV.
To determine the equilibrium potential, we need to use the Nernst equation. The Nernst equation calculates the equilibrium potential for a specific ion, such as sodium in this case. The equation is as follows:
E = (RT / zF) * ln([ion]out / [ion]in)
Where:
E - equilibrium potential
R - gas constant (8.314 J/(mol⋅K))
T - temperature in Kelvin (28°C = 28 + 273.15 = 301.15 K)
z - valence of the ion (sodium has a charge of +1, so z = 1)
F - Faraday's constant (96,485 C/mol)
[ion]out - concentration of the ion outside the cell (extracellular) = 485 mM
[ion]in - concentration of the ion inside the cell (intracellular) = 100 mM
Let's plug in the values and calculate the equilibrium potential for sodium:
E = (8.314 J/(mol⋅K) * 301.15 K) / (1 * 96485 C/mol) * ln(485 / 100)
E = (2499.899 / 96485) * ln(4.85)
E ≈ 0.02585882 * 1.58407214
E ≈ 0.04102944 V = 41.03 mV
Therefore, the equilibrium potential for sodium at a temperature of 28°C is approximately 41.03 mV.