Ultimately, f G values must be based on experimental results; in many cases, these experimental results

Ultimately, Δ_fG° values must be based on experimental results; in many cases, these experimental results are themselves obtained from E° values. Early in the twentieth century, g. N. Lewis conceived of an experimental approach for obtaining standard potentials of the alkali metals. This approach involved using a solvent with which the alkali metals do not react. Ethylamine was the solvent chosen. In the following cell diagram, Na(amalg, 0.206%) represents a solution of 0.206% Na in liquid mercury.

Although Na(s) reacts violently with water to produce H₂(g), at least for a short time, a sodium amalgam electrode does not react with water. This makes it possible to determine E_cell for the following voltaic cell.

(a) Write equations for the cell reactions that occur in the voltaic cells (1) and (2).

(b) Use equation (19.14) to establish Δ_rG for the cell reactions written in part (a).

(c) Write the overall equation obtained by combining the equations of part (a), and establish Δ_rG° for this overall reaction.

(d) Use the Δ_rG° value from part (c) to obtain E°_cell for the overall reaction. From this result, obtain E°_Na+/_Na. Compare your result with the value listed in Appendix d.

Eq. 19.14

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1. Na(s) Nat (in ethylamine) Na(amalg, 0.206%) Ecell = 0.8453 V