Question

Which of the following is calcium superphosphate? (a) \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2} \mathrm{H}_{2} \mathrm{O}+\mathrm{CaSO}_{4}\) (b) \(\mathrm{CaSO}_{4}+\mathrm{CaO}\) (c) \(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}+2 \mathrm{CaSO}_{4}\) (d) \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2} \mathrm{H}_{2} \mathrm{O}+2\left(\mathrm{CaSO}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}\right)\)

Short answer

The correct answer is (a): \(\mathrm{Ca(H_2PO_4)_2H_2O} + \mathrm{CaSO_4}.\)

Step-by-step solution

Understanding Superphosphate

Calcium superphosphate is a mixture used primarily as a fertilizer. It is produced by the reaction of calcium phosphate with sulfuric acid, resulting in a mixture containing mainly calcium dihydrogen phosphate, \[ \text{Ca} (\text{H}_2 \text{PO}_4 )_2, \]and calcium sulfate, \[ \text{CaSO}_4.\] This results in a complex product commonly referred to as 'superphosphate.' The key component is the presence of calcium dihydrogen phosphate along with calcium sulfate.

Analyzing the Choices

Review the chemical formulas provided:- Option (a): Contains \(\text{Ca} (\text{H}_2 \text{PO}_4 )_2 \cdot \text{H}_2\text{O} + \text{CaSO}_4\), which matches calcium superphosphate (primary ingredient being calcium dihydrogen phosphate with calcium sulfate).- Option (b): Contains \(\text{CaSO}_4 + \text{CaO}\), which does not contain calcium dihydrogen phosphate.- Option (c): Contains \( \text{Ca}_3 (\text{PO}_4)_2 + 2 \text{CaSO}_4 \), which is not a component of or equivalent to superphosphate.- Option (d): Contains \(\text{Ca} (\text{H}_2 \text{PO}_4)_2 \cdot \text{H}_2\text{O} + 2 (\text{CaSO}_2 \cdot 2 \text{H}_2\text{O})\), the inclusion of \(\text{CaSO}_2\) is incorrect as it typically should be \(\text{CaSO}_4.\)

Key concepts

Fertilizer Chemistry

Fertilizer chemistry is a field that focuses on developing and understanding materials that enhance plant growth. Superphosphate fertilizers, such as calcium superphosphate, play an essential role in agriculture. They are primarily used to supply essential nutrients like phosphorus, which enhances root development and the production of flowers and fruits.

Nutrient-rich fertilizers are formulated through chemical reactions involving natural minerals and acids. The chemistry behind these fertilizers is dictated by the elements' availability and their absorption mechanisms by plants. This leads to specific reactions that help convert raw minerals into usable forms. Superphosphate, for instance, is produced from the reaction of phosphate rock with sulfuric acid. It's an excellent source of phosphate, making it particularly valuable for agricultural practices.

Calcium Dihydrogen Phosphate

Calcium dihydrogen phosphate, \(\text{Ca} (\text{H}_2 \text{PO}_4 )_2\), is a critical component in calcium superphosphate. It is a water-soluble phosphate that provides an immediate supply of phosphorus to plants. The solubility of calcium dihydrogen phosphate makes it readily available for root uptake, ensuring the plant can efficiently utilize this nutrient.

This compound is formed by treating phosphate rock with sulfuric acid, which breaks down the natural mineral to a form that plants can readily absorb. The availability of phosphorus in a soluble form helps in faster plant growth, supporting various physiological functions like photosynthesis and energy transfer. Without this compound, soils might lack sufficient phosphorus, which could impede plant growth and yield.

Sulfuric Acid Reaction

The reaction involving sulfuric acid is essential in producing calcium superphosphate. By reacting sulfuric acid with phosphate rock, this process converts the natural minerals into a form useful for agriculture. This reaction is chemical in nature and produces calcium dihydrogen phosphate and calcium sulfate as its primary products.

The equation for this reaction can be represented as:

\[\text{Ca}_5 (\text{PO}_4)_3 \text{Cl} + 5 \text{H}_2 \text{SO}_4 \rightarrow 3 \text{Ca} (\text{H}_2 \text{PO}_4 )_2 + \text{CaSO}_4\]

This sophisticated chemical reaction employs sulfuric acid to liberate phosphorus, which would otherwise remain locked in its mineral form, unusable by plants. The formation of Calcium sulfate as a by-product ensures that no waste material is left behind.

Calcium Sulfate

Calcium sulfate, \( \text{CaSO}_4 \), is another important component in calcium superphosphate. Aside from being a by-product of the sulfuric acid reaction, it also provides secondary benefits. It supplies calcium, which is crucial for cell wall development in plants, and helps improve soil structure.

Calcium sulfate exists in a few hydrated forms, such as gypsum (which is \( \text{CaSO}_4 \. 2\text{H}_2 \text{O} \)) and provides a means for moderately increasing soil acidity. This can improve nutrient availability and help counteract soil alkalinity. Its presence in superphosphate not only enhances the fertilizer’s nutritional profile but also contributes to improving overall soil health.