Understanding pE and Redox Conditions

The pE value represents the redox potential of a system, similar to how pH represents acidity. It indicates whether a system is oxidizing (high pE) or reducing (low pE).

• High pE values (e.g., > 7) indicate strongly oxidizing conditions.
• Low pE values (e.g., < 0) indicate strongly reducing conditions.
• Intermediate values represent varying degrees of oxidizing or reducing potential.

Relating pE to Dissolved Oxygen (DO)

Dissolved oxygen (O₂) is a molecule that exists in its oxidized state. It is most stable and typically found in higher concentrations under oxidizing conditions.

Conversely, in highly reducing environments (low pE), oxygen can be consumed or reduced to other chemical species, leading to lower dissolved oxygen concentrations.

Comparing pE Values for Water Samples

The pE values provided for the four water samples are:

• pE = – 4.1 (Strongly reducing)
• pE = 1.0 (Slightly oxidizing/neutral)
• pE = 7.0 (Neutral/mildly oxidizing)
• pE = 13.9 (Strongly oxidizing)

Determining Highest Dissolved Oxygen Concentration

The highest concentration of dissolved oxygen (O₂) is expected in the sample with the most oxidizing conditions. Comparing the given pE values, pE = 13.9 is the highest value, indicating the strongest oxidizing environment.

Therefore, the concentration of dissolved oxygen shall be highest in the water sample with pE = 13.9.