Correct option is C
The correct answer is
(c) H₂PO₄⁻.
In natural waters with a pH range of 3-7, the dominant phosphorus species is
dihydrogen phosphate (H₂PO₄⁻). The distribution of phosphate species in water depends on the pH value. At a pH range between 3 and 7:
·
At lower pH (around 3),
H₃PO₄ (phosphoric acid) is present.
·
Between pH 3-7,
H₂PO₄⁻ (dihydrogen phosphate) is the dominant species.
·
At pH values above 7,
HPO₄²⁻ (hydrogen phosphate) becomes dominant.
·
Above pH 12,
PO₄³⁻ (orthophosphate) dominates.
Information Booster:
1.
pH and Phosphorus Species:
·
pH < 3: Dominated by
H₃PO₄.
·
pH 3-7: Dominated by
H₂PO₄⁻.
·
pH 7-11: Dominated by
HPO₄²⁻.
·
pH > 12: Dominated by
PO₄³⁻.
2.
Phosphate Speciation:
· The speciation of phosphorus is crucial in understanding nutrient availability and eutrophication in water bodies.
3.
Insoluble Compounds:
·
Insoluble Fe/Al phosphate precipitates in acidic conditions.
·
Insoluble Ca phosphate precipitates in alkaline conditions.
4.
Environmental Impact:
· Phosphorus availability affects aquatic ecosystems, and its speciation influences the risk of algal blooms.
Additional Knowledge:
1.
(a) Insoluble Fe/Al Phosphate:
· Forms under acidic conditions and low pH (<5).
· Common in acidic soils or waters where iron and aluminum are present.
2.
(b) Insoluble Ca Phosphate:
· Precipitates in alkaline conditions (pH > 7).
· Common in calcareous soils and hard water.
3.
(c) H₂PO₄⁻:
· Dominant in a moderate pH range (3-7).
· Available for plant uptake and critical in nutrient cycling.
4.
(d) HPO₄²⁻:
· Predominant in slightly alkaline conditions (pH 7-11).
· Important in wastewater treatment and natural waters with higher pH.
Key Points:
1.
H₂PO₄⁻ is the primary phosphate species in waters with pH 3-7.
2. Phosphorus speciation affects
nutrient dynamics and
eutrophication.
3.
pH controls the solubility and availability of phosphorus compounds.
4. Different insoluble phosphates form under varying pH conditions.
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