how do i calculate a ratio of oxidised to reduced cytochrome c Fe2+ to Fe3+
given
E(mV) at 25 C and pH7 as 100
and absorbance at 550nm as 1.5
E is relative to standard hydrogen electrode
i don't know how im supposed to calculate it from this data
To calculate the ratio of oxidized (Fe3+) to reduced (Fe2+) cytochrome c, you need to understand the concept of the Nernst equation and how it relates to electron transfer reactions.
The Nernst equation is given by:
E = E˚ + (RT/nF) * ln([ox]/[red])
Where:
E is the measured potential in volts
E˚ is the standard electrode potential in volts
R is the ideal gas constant (8.314 J/(mol·K))
T is the temperature in Kelvin
n is the number of electrons transferred in the reaction
F is the Faraday constant (96485 C/mol)
[ox] and [red] are the concentrations of the oxidized and reduced species, respectively
In this case, cytochrome c can be oxidized from Fe2+ to Fe3+, so the number of electrons transferred is 1 (n = 1).
Given that the E value at 25°C and pH 7 for the Cytochrome c redox couple is 100 mV relative to the standard hydrogen electrode, we can substitute the values into the Nernst equation.
E = 0.10 V + (8.314 J/(mol·K)) * (298 K) / (1 * 96485 C/mol) * ln([Fe3+]/[Fe2+])
Now, you need to use the absorbance at 550 nm (1.5) to determine the concentration ratio of [Fe3+]/[Fe2+].
The absorbance of a substance is directly proportional to the concentration following Beer-Lambert's law, which states:
A = εcl
Where:
A is the absorbance
ε is the molar absorptivity (a constant depending on the substance and the wavelength)
c is the concentration
l is the path length of the cuvette (usually 1 cm)
We can rearrange the equation to determine the concentration:
c = A / (εl)
Since the molar absorptivity (ε) and the path length (l) are not given, we cannot calculate the exact concentrations of Fe3+ and Fe2+ directly.
However, you can still use the Nernst equation to determine the ratio of [Fe3+]/[Fe2+] using the absorbance value:
E = 0.10 V + (8.314 J/(mol·K)) * (298 K) / (1 * 96485 C/mol) * ln([Fe3+]/[Fe2+])
We can assume that the standard electrode potential (E˚) for the cytochrome c redox couple is zero, as it is not provided. This simplifies the equation:
E = (8.314 J/(mol·K)) * (298 K) / (1 * 96485 C/mol) * ln([Fe3+]/[Fe2+])
Now, substitute the absorbance value (A = 1.5) to the equation to get the ratio:
(8.314 J/(mol·K)) * (298 K) / (1 * 96485 C/mol) * ln([Fe3+]/[Fe2+]) = 1.5
You can rearrange the equation to solve for the ratio [Fe3+]/[Fe2+].