Answer: True. The charge on organic humic materials is indeed due to protonation-deprotonation reactions at acid function groups.
Step-by-step explanation:
Organic humic materials, such as humic acids and fulvic acids, are complex mixtures of organic compounds found in soil, water, and sediment. These materials contain acid function groups, such as carboxylic acid groups (COOH) and phenolic hydroxyl groups (OH), which can undergo protonation and deprotonation reactions.
Protonation refers to the addition of a proton (H+) to a molecule, resulting in a positively charged species. Deprotonation, on the other hand, involves the removal of a proton, resulting in a negatively charged species.
In the case of organic humic materials, the acid function groups can donate or accept protons depending on the pH of the surrounding environment. At low pH (acidic conditions), these groups tend to be protonated and carry a positive charge. As the pH increases (becomes more basic), the acid function groups deprotonate and become negatively charged.
The protonation-deprotonation reactions of acid function groups in organic humic materials contribute to their overall charge and influence their behavior in various environmental processes. For example, the charged nature of humic substances affects their interactions with other molecules, such as metal ions, and can influence processes like nutrient cycling and pollutant adsorption.