Question

Single super phosphate contains:
A. $20\% $ of ${P_2}{O_5}$
B. $16$ to $18\% $ ${P_2}{O_5}$
C. $20$ to $25\% $ ${P_2}{O_5}$
D. $10$ to $46\% $ ${P_2}{O_5}$

Answer 1

Hint: The phosphate rock, which is primarily tricalcium phosphate, $C{a_3}{\left( {P{O_4}} \right)_2}$ and apatite, $Ca{F_2}.3C{a_3}{\left( {P{O_4}} \right)_2}$, are too little soluble in water to serve as a source of phosphorus for plants. These are, therefore, converted into calcium dihydrogen phosphate which is commonly known as calcium superphosphate. This is the most important phosphatic fertilizer. Other such fertilizers are triple phosphate, phosphatic slag, and nitro phosphate.

Complete step by step answer:
Calcium Superphosphate is manufactured by treating the insoluble phosphate rock with a calculated quantity of sulphuric acid (commercial) when we get the more soluble calcium dihydrogen phosphate (superphosphate) and calcium sulphate. The reaction involved in this process is written below:

$C{a_3}{\left( {P{O_4}} \right)_2} + 2{H_2}S{O_4} \to 2CaS{O_4} + Ca{\left( {{H_2}P{O_4}} \right)_2}$

A sufficient amount of water is then added to convert calcium sulphate into its dihydrate, $CaS{O_4}.2{H_2}O$ (gypsum).

The mixture of calcium dihydrogen phosphate and gypsum is marketed under the name of superphosphate of lime and is used as a fertilizer. It is soluble in water and contains $16$ to $18\% $ ${P_2}{O_5}$ , it is considered as a good phosphatic fertilizer. However, care should be taken in its storage as it tends to set in the form of hard lumps.

After discussing we can conclude that single superphosphate contains $16$ to $18\% $ ${P_2}{O_5}$.

So, the correct answer is Option B.

Note: Plants require phosphorus, potassium, nitrogen, sulphur, calcium, iron, and magnesium, besides traces of a few other elements such as copper, boron, zinc, manganese, molybdenum, and cobalt for their growth and health. These elements are generally present in the soil to more or less extent in the form of minerals or otherwise. However, after a few years of continuous cropping, the soil becomes poorer and poorer in these materials and there is a need to put back what has been taken out from the soil by successive crops. If the soil is not replenished by what it has lost, in time, it would be less productive and, in extreme cases may become even fertile. To keep up soil fertility and to get good yields of various crops, it is necessary to add materials containing nitrogen, phosphorus, and potassium in the form of manures which may be natural or artificial. The artificial manures are called chemical fertilizers. Nitrogen, potassium, and phosphorus are regarded as essential plant nutrients.