Varying the concentrations of half-cells

[~angel~]

I'm not sure ow to do this question.

Calculate the reduction potential of a half-cell consisting of a platinum electrode immersed in a 2.0M Fe2+ and 0.2M Fe3+ solution 25c.

Thanks.

 

[Dr.Brain]

The Nernst Equation is given by:

<br /> E= E_o - \frac{0.059}{n} log \frac{N_1}{N_2}<br />

The above half cell reaction can be written as:

<br /> Fe^2^+ ------&gt; Fe^3^+ e^_<br />


here n=1 as you can see in the cell reaction.

 

[thepatientmental]

To calculate the reduction potential of this half-cell, we can use the Nernst equation: Ecell = E°cell - (RT/nF)lnQ, where Ecell is the cell potential, E°cell is the standard cell potential, R is the gas constant, T is the temperature in Kelvin, n is the number of electrons transferred in the reaction, F is Faraday's constant, and Q is the reaction quotient.

First, we need to determine the standard cell potential (E°cell) for the half-cell. This can be found by looking up the standard reduction potentials for the Fe2+/Fe3+ redox couple. According to the NIST Chemistry WebBook, the standard reduction potential for this couple is 0.771 V at 25°C.

Next, we need to calculate the reaction quotient (Q) using the concentrations of Fe2+ and Fe3+ given in the question. Q = [Fe3+]/[Fe2+] = 0.2/2.0 = 0.1.

Now we can plug in all the values into the Nernst equation and solve for Ecell:

Ecell = 0.771 V - (8.314 J/mol·K)(298 K)/(1 mol)(96,485 C/mol)ln(0.1) = 0.771 V - 0.059 V = 0.712 V

Therefore, the reduction potential for this half-cell is 0.712 V at 25°C. This means that at standard conditions, the reaction is spontaneous and favors the reduction of Fe3+ to Fe2+. Varying the concentrations of the half-cell can affect the reaction quotient and therefore change the cell potential. This can be seen by plugging in different values for Q in the Nernst equation and observing the resulting changes in Ecell.