Electrochemistry Practice Test

In cyclic voltammetry, a reversible redox couple shows a clean, mirror-like pair of peaks: the reduction peak and the oxidation peak are well separated in potential but symmetric in current. For a simple diffusion-controlled one-electron transfer at room temperature (25°C), the peak-to-peak separation ΔEp is about 59/n millivolts, where n is the number of electrons transferred. The currents at the two peaks have equal magnitude but opposite sign, i_p,a ≈ - i_p,c, reflecting that the same amount of species is oxidized and reduced during the cycle.

The behavior with scanning rate is predictable for a reversible couple: ΔEp stays close to this 59/n mV value as the scan rate changes (though the peak currents scale with the square root of the scan rate). If the separation is much larger, or it varies irregularly with scan rate, or the peaks aren’t equal and opposite, that signals quasi-reversible or irreversible behavior rather than a reversible couple.

Thus, the statement describing a peak separation around 59/n mV at 25°C, with equal and opposite peak currents and predictable ΔEp behavior with scan rate, best captures how cyclic voltammetry identifies a reversible redox couple.