Question

The electrochemical cell shown can be used to calculate the formation constant (Kf​) for a metal (M) and EDTA. The cell has a potential of −0.263 V. The right half-cell contains a metal ion (M2+) with a standard reduction potential of −0.236 V. M2++2e−⇌M(s)E∘=−0.236 V Citric acid has three pKa​ values: 3.128,4.761, and 6.396. Calculate the Kf​ for the metal-EDTA complex. Kf​

Answer 1

To calculate the formation constant (Kf) for the metal-EDTA complex, we can use the Nernst equation. First, calculate the standard cell potential (E°cell) by subtracting the standard reduction potential of the metal ion (M2+) from the measured cell potential. Then, use the Nernst equation to relate E°cell to Kf. Substituting the values and solving, we find that Kf is approximately 1483.3.

Step-by-step explanation:

The formation constant (Kf) for the metal-EDTA complex can be calculated using the Nernst equation. The Nernst equation relates the measured cell potential (Ecell) to the concentrations of the species involved in the cell reaction. In this case, the metal ion (M2+) is reduced at the cathode, while EDTA is oxidized at the anode.

First, we need to calculate the standard cell potential (E°cell) using the standard reduction potentials of the metal ion (M2+) and EDTA.

The cell potential is given as -0.263 V, and the standard reduction potential of M2+ is -0.236 V. So, E°cell = Ecell + E°cathode = -0.263 V - (-0.236 V) = -0.027 V.

Next, we can use the Nernst equation to relate the standard cell potential (E°cell) to the formation constant (Kf). The Nernst equation is: Ecell = E°cell - (0.0592/n) * log10(Kf).

Here, n represents the number of electrons transferred in the cell reaction, which is 2 for the reduction of M2+ to M(s).

To calculate Kf, we can rearrange the Nernst equation: log10(Kf) = (E°cell - Ecell) * (n/0.0592)

Substituting the values, we get log10(Kf) = (-0.027 V - (-0.236 V)) * (2/0.0592) = 3.188. Taking the antilog of both sides, we find Kf = 10^3.188 = 1483.3