Superphosphate of Lime Production

Superphosphate of lime is a phosphate fertilizer created by chemically treating calcium phosphate.

Calcium Phosphate Reaction

The production involves reacting insoluble calcium phosphate (\(\text{Ca}_3\text{(PO}_4)_2\)), found in phosphate rock, with a strong acid. To produce single superphosphate (SSP), the acid used is sulfuric acid (\(\text{H}_2\text{SO}_4\)).

The specific reaction is:

\( \text{Ca}_3\text{(PO}_4)_2 \text{ (insoluble)} + 2 \text{H}_2\text{SO}_4 \text{ (aq)} \rightarrow \text{Ca(H}_2\text{PO}_4)_2 \text{ (soluble)} + 2 \text{CaSO}_4 \text{ (aq)} \)

This reaction converts the poorly soluble tricalcium phosphate into monocalcium phosphate, which is soluble in water and readily available to plants, along with calcium sulfate (gypsum).

Reasoning for Correct Option

The reaction between calcium phosphate and sulphuric acid directly yields the soluble phosphate compounds necessary for a fertilizer, known as superphosphate of lime. Reacting calcium phosphate with other substances like sodium hydroxide, hydrogen chloride, or nitric acid does not produce this specific fertilizer.

• Sodium hydroxide is a base and would react differently, potentially forming other salts but not the desired soluble phosphates.
• Hydrogen chloride and nitric acid, while acids, are not typically used for producing standard superphosphate fertilizer from calcium phosphate in this manner. Sulfuric acid is the specific reagent for single superphosphate.