The three primary nutrients a fertiliser supplies are
Answer: A
These three are needed in the largest quantity and are what an NPK grade reports. Calcium and sulphur are secondary nutrients and the metals are micronutrients. A grade reports only these three. The others are supplied separately when a soil lacks them.
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An NPK grade of 20-20-0 means the fertiliser contains
Answer: B
The numbers are percentages by mass, reported as nitrogen, phosphorus pentoxide and potassium oxide by convention. The oxide convention is a historical one but is universal in the trade. Grades are always written in that order.
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Assertion (A): Phosphate content is conventionally reported as phosphorus pentoxide rather than as phosphorus.
Reason (R): The convention dates from an era of oxide-based analysis and has been kept for continuity.
Answer: C
Both are true and the reason gives the origin: potash is likewise reported as potassium oxide, so converting an analysis to the elements requires a factor for each of the two nutrients. The factors are a little under one half in both cases.
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Ammonia is synthesised industrially by the
Answer: D
Nitrogen comes from air and hydrogen usually from natural gas by steam reforming. The other three named processes make nitric acid, soda ash and sulphuric acid respectively. Hydrogen usually comes from steam reforming.
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Consider the following statements about ammonia synthesis conditions.
1. High pressure favours the equilibrium because moles decrease.
2. Low temperature favours the equilibrium because the reaction is exothermic.
3. The process is run at low temperature to maximise the yield.
Answer: A
The first two are correct but the third does not follow, because at low temperature the rate is impractically slow and a compromise temperature around four hundred and fifty degrees is used instead. Recycle makes up for the modest single pass conversion.
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State whether the following is true or false.
Ammonia synthesis is run at the temperature that gives the best equilibrium conversion.
Answer: B
Correct answer: False
Ammonia synthesis is exothermic, so equilibrium favours the lowest temperature - at which the rate over the iron catalyst is negligible. The plant runs at 400 to 500 degrees, accepting a poorer equilibrium for a workable rate, and recovers the lost yield by operating at 150 to 250 bar and recycling the unconverted gas. It is the standard illustration of a kinetic and thermodynamic compromise.
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Urea is manufactured from
Answer: C
Ammonium carbamate forms first and then dehydrates to urea, and both steps occur in the same reactor. The carbon dioxide comes conveniently from the reforming section of the ammonia plant. The two steps share the same high pressure reactor.
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Assertion (A): Urea plants are almost always built alongside ammonia plants.
Reason (R): The ammonia plant supplies both the ammonia and the carbon dioxide that urea requires.
Answer: D
Both are true and the reason gives the integration: the reformer produces carbon dioxide that would otherwise be vented, so the two plants together use both streams that neither could use alone. Site integration is the rule in this industry.
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Match each nitrogen fertiliser with its nitrogen content.
List I
A. Urea
B. Ammonium nitrate
C. Ammonium sulphate
D. Calcium ammonium nitrate
List II
1. about 21 per cent
2. about 46 per cent
3. about 26 per cent
4. about 34 per cent
Answer: A
Correct answer: A-2, B-4, C-1, D-3
The nitrogen contents follow from the formulae. Urea, \( \mathrm{CO(NH_2)_2} \), is 46 per cent nitrogen - the highest of any solid fertiliser, which is why it dominates world trade. Ammonium nitrate is 34, ammonium sulphate 21, and calcium ammonium nitrate 26, being ammonium nitrate diluted with limestone to make it safer to store and handle.
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Urea is the most widely traded nitrogen fertiliser mainly because
Answer: B
At about forty-six per cent nitrogen it carries the least dead weight per unit of nutrient, which dominates shipping economics. Its drawback is loss of ammonia by volatilisation if it is not incorporated into the soil.
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