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## Nernst Equation Notes This is an extract of our Nernst Equation document, which we sell as part of our BIOL10832 Excitable Cells Notes collection written by the top tier of University Of Manchester students.

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e-learning III - Nernst Equation

The Nernst Equation predicts when an electrical gradient (E) and a chemical gradient are in balance. It was originally formulated to describe the behaviour of electrochemical cells
(batteries).

 In this equation, z is the charge on the ion, R is the ideal gas constant (8.314 J.K-1.mol-1),
F is the Faraday constant (9.65x104 C.mol-1), T is the temperature in Kelvin (273 K = 0 ˚C)
and E is the equilibrium potential for the ion (in V).

 Use this information to determine the equilibrium potential at 21 ˚C, for Ca 2+in a cell where
[Ca2+ outside] = 5 mM and [Ca2+ inside] = 0.1 mM.

E=

8.314 ×(21+273)
5 ×10−3
[
] = 0.0495V (49.5 mV)
ln 2 ×9.65 ×10 4

0.1 ×10−3

 At 37˚C, the equilibrium potential for Cl- in a cell is -61.5 mV. If the intracellular concentration of Cl- is 15 mM, what is the concentration of chloride outside the cell?

-61.5x10-3 V =

x 8.314 ×(37+273)
]
ln[
4 15 ×10−3
−1 × 9.65× 10

-61.5x10-3 V = -0.0267 ln[

2.303 = ln[

x ]
15 ×10−3

x ]
15 ×10−3

e2.303 (10.0041) =

x 15× 10−3

10.0041 x 15x10-3 = 0.15M (150mM)
 At 30˚C the equilibrium potential for ion X is 30.1 mV. The concentration of X outside the cell is 10 mM and inside the cell it is 1 mM. What is the valence of ion X?

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