Nernst equation calculator4/7/2023 ![]() Z = valency of ion (Na + is plus one, Ca 2+ is plus two and Cl - is minus one)į = Faraday’s constant, 9.684 x 10 4 C mol -1 Some of you may already have seen that the Nernst equation is expressed in another form that is used in some textbooks:Ģ.303 is a conversion factor from natural log to log 10 The explanation is that equation 1 is rather simplified. You may have wondered why it should be 58 mV? What is so magical about the number 58? Perhaps you have been puzzled by different values in textbooks, 61 mV, perhaps. The membrane potential difference between these two points is 58 mV (difference between -66.5 and -8.5 mV). The arrows in figure 1 are separated by 1 log unit, or put another way, they mark a 10-fold concentration difference. You also learned that the slope of the line should have a value of 58 mV for a 10-fold concentration difference at room temperature (rising to about 61 at 37 o C). So, you should know (from your lectures that) a plot of log of the K concentration (x axis) against membrane potential gives a straight line (is a linear function) if the membrane is perfectly selective for potassium ions. This equation defines the relation between the concentrations of an ion on either side of a membrane that it perfectly selective for that ion and the potential difference (voltage) that will be measured across that membrane under equilibrium conditions.Īs we discussed in the practical class, the Nernst equation is able to give a value for the voltage that must exist across the membrane in order to balance a chemical gradient that exists for the ion in question. You probably recognise equation 1 as the Nernst equation.
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