Florida Drinking Water Operator "B" Practice Test

The reaction of dissolved oxygen with ferrous ions is reduced during which condition?

1. High pH

2. Low pH

3. Normal temperature

4. Excessive turbidity

The correct answer is: Low pH

The reaction of dissolved oxygen with ferrous ions is reduced in low pH conditions due to the increased acidity affecting the solubility and reactivity of ferrous ions. In acidic environments, the concentration of hydrogen ions increases, which can cause ferrous ions (Fe²⁺) to oxidize more readily to ferric ions (Fe³⁺). This process diminishes the levels of ferrous ions available to react with dissolved oxygen, thus reducing the overall rate of the oxidation reaction. In contrast, at higher pH levels, the conditions are more favorable for ferrous ions to remain in solution and react with dissolved oxygen, as less hydrogen ion concentration is present to influence their oxidation. Temperature typically affects reaction rates but does not inherently favor or inhibit the reaction of ferrous ions with oxygen in the same manner as pH does. Excessive turbidity primarily impacts light penetration and can introduce other materials that may interact with ions, but it does not directly influence the acid-base balance and the oxidation state of ferrous ions as significantly as low pH.