Calcium standard reduction potentials

The standard reduction potentials, particularly those of the heavier congeners, are similar to those of the heavier alkali metals. These are all good reducing agents. The near-constancy of the E° values of calcium, strontium, barium, and radium reflects a balance of the heats of atomization, ionization, and hydration energies. (See Problem 13.23.) Of course, two electrons must be ionized from the alkaline... 

Analyze what happens when calcium is added to water, using the standard reduction potentials given in Table 12.2. Calculate both the overall Ef" and the AG° for the reaction. 

Set up thermochemical cycles for the reduction of calcium, strontium, and barium ions to the free metals. Determine the enthalpy of these reductions, LH i Ca), A//red(Sr), and A//jed(Ba), using the data provided on the next page. Briefly relate your results to the standard reduction potentials of these three elements. 

This reference electrode system is suitable for use between 700 and 950 °C, below which the reference system has too high impedance (typically above 10 2) and above which the silver melts T = 962 °C). Internal standards are used to measure the stability of the electrode. Here, reduction of silicon dioxide and calcium metal deposition (from Ca " ) can be used as indicator potentials and show that the electrode can give stable potentials for times between hours and days. In practice, while carrying out long electrolysis reactions in chloride melts, the group at CSIRO (Australia) have found that the electrodes typically last about 8 h. This is, however, sufficient to carry out many types of experiments. 

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