The element highlighted as largely absent from ocean water, specifically in the form of its insoluble oxide as per the provided reference, is Iron.
Understanding the Absence of Iron in Ocean Water (in specific forms)
While numerous elements are present in ocean water, often in trace amounts or various dissolved forms, the provided reference offers a specific insight regarding Iron. It explicitly states:
"Iron(III) oxide is insoluble in water but dissolves readily in strong acid, e.g. hydrochloric and sulfuric acids. It is not found in Oceans."
This critical piece of information directly addresses the presence of a specific compound containing the element Iron (Fe). Iron(III) oxide (Fe₂O₃) is an insoluble compound of iron. Its stated absence in oceans signifies that iron, when present in this particular insoluble oxide form, is generally not found in these aquatic environments.
Key Insights:
- Compound vs. Element: The reference precisely notes the absence of Iron(III) oxide (a chemical compound), rather than a blanket statement about the element Iron itself in all its possible forms.
- Form and Solubility Matter: Although Iron(III) oxide is explicitly stated as not found, it's crucial to understand that the element Iron can exist in ocean water. However, it is typically present in:
- Dissolved ionic forms (e.g., Fe²⁺, Fe³⁺), often complexed with organic ligands.
- Colloidal particles, which are extremely small, dispersed particles that do not readily settle out.
- Associated with suspended particulate matter, such as dust or biological debris.
- Environmental Conditions: The insolubility of Iron(III) oxide in the typically neutral to slightly alkaline pH range of ocean water (which is generally between 7.5 and 8.4) explains why this specific compound does not readily accumulate. Its dissolution would require much more acidic conditions than those naturally found in the ocean. The availability of iron, even in trace amounts, is a vital nutrient for marine organisms, particularly phytoplankton, underscoring the complexity of its biogeochemical cycle in the ocean.
Therefore, based on the specific information provided, the element Iron is implicated through the explicit absence of its insoluble Iron(III) oxide compound in ocean water.
