Question 1

In the urea process, which product results directly from the dehydration of ammonium carbamate under high-pressure reactor conditions?

Accepted Answer

Introduction / Context: Commercial urea manufacture proceeds by first forming ammonium carbamate from ammonia and carbon dioxide, followed by its dehydration to urea and water. Understanding this step is fundamental in nitrogenous fertilizer technology and plant troubleshooting. Given Data / Assumptions: Feed mixture at high pressure contains NH3 and CO2. Ammonium carbamate is the intermediate species. Reaction pathway: carbamate → urea + H2O (endothermic dehydration). Concept / Approach: The net reaction to urea is 2 NH3 + CO2 → NH2CONH2 + H2O via the carbamate intermediate. Biuret forms only as a side product by condensation of urea molecules at higher temperatures or prolonged residence. “Ammonia water” is not a process product of the dehydration step; rather, excess NH3 is recovered in recycle sections. Step-by-Step Solution: Form ammonium carbamate in the reactor from NH3 and CO2.Apply dehydration (heat/pressure conditions) to convert carbamate to urea + water.Recognize that biuret requires urea–urea condensation, not direct carbamate dehydration.Therefore, the direct product is urea. Verification / Alternative check: Process flow diagrams show high-pressure synthesis leading to urea solution, followed by recovery/stripping and finishing; biuret control is a specification issue in prilling/granulation, not the primary synthesis step. Why Other Options Are Wrong: Biuret: secondary byproduct from urea, not from carbamate dehydration.Ammonia water: not a defined product of the key dehydration reaction.“None of these” is incorrect because urea is correct. Common Pitfalls: Confusing the intermediate (carbamate) with byproducts; assuming higher temperature necessarily improves conversion without raising biuret formation. Final Answer: Urea

Question 2

Within India’s fertilizer industry, which plant historically obtained hydrogen via electrolysis of water for ammonia synthesis feed preparation?

Accepted Answer

Introduction / Context: Hydrogen for ammonia synthesis is usually produced by natural-gas steam reforming or naphtha reforming. However, certain plants have used water electrolysis, particularly where inexpensive hydroelectric power is available. Recognizing such exceptions is a classic exam topic in fertilizer technology. Given Data / Assumptions: Electrolysis of water takes significant electrical energy. Locations with access to hydropower historically adopted this route. The question asks for the specific Indian plant known for this practice. Concept / Approach: Nangal (Punjab) is well known for integrating hydroelectric power from the Bhakra-Nangal project, enabling hydrogen generation by water electrolysis for its ammonia unit, especially in earlier configurations before widespread gas-based reforming dominance. Step-by-Step Solution: Identify which site aligns with hydroelectric infrastructure.Nangal corresponds to Bhakra-Nangal hydropower, making electrolysis economical at that time.Select Nangal as the plant obtaining H2 by electrolysis. Verification / Alternative check: Historical plant summaries and training manuals routinely cite Nangal as the example of electrolysis-based hydrogen in Indian ammonia production. Why Other Options Are Wrong: Namrup, Rourkela, Korba: these sites are associated with alternate feedstocks or steel/chemical complexes, not the classic electrolysis case. Common Pitfalls: Assuming all fertilizer hydrogen is from reforming; overlooking legacy processes adapted to local power sources. Final Answer: Nangal

Question 3

Bone ash, a traditional phosphate source used in fertilizer and metallurgy, is composed predominantly of which calcium compound?

Accepted Answer

Introduction / Context: Bone ash originates from calcined animal bone and has been a historical source of phosphorus. Understanding its composition explains its applications in fertilizer blending, ceramics, and metallurgy as a source of phosphorus pentoxide equivalents. Given Data / Assumptions: Bone ash is produced by high-temperature treatment of bones. Residual inorganic matrix mirrors the mineral phase of bone. We seek the dominant chemical component. Concept / Approach: Natural bone mineral is hydroxyapatite, Ca10(PO4)6(OH)2, which upon calcination yields materials collectively referred to as calcium phosphates. Therefore, the principal constituent of bone ash is calcium phosphate (apatite family), not calcium sulfate or carbonate as the main phase. Step-by-Step Solution: Link bone mineral to hydroxyapatite composition.Calcination removes organics and water, concentrating phosphate salts.Recognize that calcium phosphate dominates bone ash composition.Select calcium phosphate as the main component. Verification / Alternative check: Materials references list bone ash as primarily tricalcium phosphate/hydroxyapatite; analytical assays show high P2O5 content consistent with calcium phosphate matrices. Why Other Options Are Wrong: Calcium sulfate and calcium carbonate may be present as minor phases or contaminants but are not the predominant bone-derived mineral.Sodium phosphate is not a natural bone mineral and would require chemical processing to appear. Common Pitfalls: Confusing bone ash with phosphate rock (both phosphate sources) or supposing gypsum dominates due to fertilizer associations. Final Answer: Calcium phosphate

Question 4

White and red phosphorus exhibit different physical and chemical properties. Which statement is true for both white phosphorus and red phosphorus?

Accepted Answer

Introduction / Context: Allotropes of phosphorus differ in reactivity and solubility. White phosphorus is highly reactive, pyrophoric when finely divided, and soluble in CS2; red phosphorus is more polymeric, less reactive, and insoluble in CS2. Questions often test recognition of properties that apply to one or both allotropes. Given Data / Assumptions: Allotropes considered: white and red phosphorus only. We seek a property valid for both forms. Conditions: typical laboratory/industrial handling under air and heating. Concept / Approach: Combustion behavior: both allotropes will burn in air when sufficiently heated, forming phosphorus oxides. Solubility: only white P is soluble in carbon disulfide; red P is insoluble. Reaction with hot concentrated alkali to produce phosphine is characteristic of white P; red P is far less reactive, and the same reaction does not proceed comparably under standard conditions. Step-by-Step Solution: Evaluate CS2 solubility: true for white P; false for red P.Evaluate combustion: both can combust when heated in air, though white P ignites more readily.Evaluate reaction with hot alkali: characteristic for white P; not reliably for red P under standard conditions.Therefore, the common true statement is that both burn when heated in air. Verification / Alternative check: References list red P as less reactive yet combustible at elevated temperatures; white P is readily combustible and must be stored under water to prevent oxidation/ignition. Why Other Options Are Wrong: Solubility in CS2 applies only to white P.Reaction with hot caustic to give phosphine is primarily a property of white P; red P does not behave the same way in typical conditions.“All of the above” fails because (a) and (c) are not universally true. Common Pitfalls: Assuming similar behavior due to same element; overlooking allotrope-specific properties, especially solubility and reactivity differences. Final Answer: Both burn when heated in air.

Question 5

Unlike catalytic SO2 oxidation, ammonia synthesis is not implemented as multiple separate reactor stages in series. What is the principal reason for avoiding true multistage operation in NH3 synthesis?

Accepted Answer

Introduction / Context: Ammonia synthesis is equilibrium-limited and exothermic. Modern converters use internal multibed arrangements with interbed cooling or quenching within a single pressure shell. The question contrasts this with processes like SO2 oxidation that can deploy multiple separate beds in separate vessels. Given Data / Assumptions: Ammonia reactors operate at high pressures (often >100 bar). Catalyst is iron-based with heat management via interbed exchangers or quench gas. Objective is to understand why not use multiple separate reactors in series. Concept / Approach: While pressure drop and pumping are relevant, the dominant constraint is economics: duplicating thick-walled high-pressure reactor shells is extremely costly. Therefore, designers place multiple catalyst beds inside one shell to achieve quasi-multistage temperature control and conversion while paying for only one pressure boundary and one set of costly high-pressure internals. Step-by-Step Solution: List potential drawbacks of true multistage vessels: more pressure boundaries, interconnecting high-pressure piping, additional safety systems.Identify the largest cost driver: multiple HP shells with thick walls dominate CAPEX.Recognize engineering practice: multibed internals inside one shell mitigate this.Select high capital cost of multiple HP shells as primary reason. Verification / Alternative check: Converter designs (e.g., three-bed radial-flow internals) achieve desired temperature profiles with minimal additional shell resources, confirming the economic rationale against separate staged vessels. Why Other Options Are Wrong: Pressure drop exists but is handled by internal design; it is not the primary barrier.Pumping cost is not a central factor in a loop dominated by compressor duty.Entrainment/bed disturbance are engineering issues but not the decisive reason versus shell cost. Common Pitfalls: Confusing internal multibed staging (common) with multiple separate pressure vessels (rare due to cost). Final Answer: High capital cost of multiple high-pressure reactor shells

Question 6

From an economic standpoint in modern fertilizer complexes, what is the approximate optimum single-train size for an ammonia plant (in tons NH3 per day)?

Accepted Answer

Introduction / Context: Plant “optimum size” balances economies of scale with capital intensity, reliability, and market/logistics constraints. Historically, single-train ammonia units scaled from a few hundred to over a thousand tons per day as technology improved and global demand rose. Given Data / Assumptions: “Optimum” refers to a commonly cited economic sweet spot in classical exam literature. Comparative options span 10, 100, and 1000 t/d, representing small pilot, mid, and large commercial scales. We ignore cutting-edge mega-trains and focus on standard textbook benchmarks. Concept / Approach: Economies of scale favor larger trains up to a point, beyond which risks, logistics, and capital costs temper benefits. Traditional chemical technology texts cite about 1000 t/d as the representative optimum size for an ammonia plant, reflecting a balance of compressor size, loop equipment, and downstream urea integration at the time of reference. Step-by-Step Solution: Review capacity ranges used in industry and textbooks.Recognize diminishing returns in scale-up costs beyond around 1000 t/d in classical analyses.Match to provided choices: 1000 t/d fits the cited optimum.Select 1000. Verification / Alternative check: While modern mega-plants can exceed 2000 t/d per train, exam problems traditionally anchor “optimum” at 1000 t/d. The answer reflects that conventional teaching benchmark. Why Other Options Are Wrong: 10 and 100 t/d are too small to capture economies of scale for world-scale ammonia.“1000C” is not a valid capacity figure; appears to be a typographical decoy. Common Pitfalls: Applying current mega-train capacities to legacy “optimum size” questions without noting the exam’s conventional context. Final Answer: 1000

Question 7

In fertilizer chemistry, what is the correct condensed structural formula for biuret (the dimerization product formed when urea is overheated)?

Accepted Answer

Introduction / Context: Biuret is a well-known impurity that can form when urea-based fertilizers are overheated or held too long at elevated temperature during processes such as melting and prilling. Understanding the correct structure of biuret is important for fertilizer quality control because excessive biuret can be phytotoxic, especially to sensitive crops and foliar applications. Given Data / Assumptions: The question asks for the correct condensed structural formula of biuret. Biuret forms by condensation (with loss of ammonia) from urea molecules. We use standard, text-friendly condensed formulas without special drawing tools. Concept / Approach: Urea has the formula NH2CONH2. When two urea units condense, one –NH2 group and one –CO–NH– portion react with release of NH3, yielding a molecule that contains two carbonyl groups linked through a single bridging –NH–: H2N–CO–NH–CO–NH2. In condensed form, this is written as NH2CONHCONH2. Recognizing the repeating –CO–NH– motif is the key to distinguishing biuret from urea and from carbamate-type salts. Step-by-Step Solution: Start with urea: NH2CONH2.Overheating promotes condensation of two urea molecules with elimination of NH3.The product contains two carbonyls connected by –NH–, giving H2N–CO–NH–CO–NH2.Write as a single condensed string: NH2CONHCONH2. Verification / Alternative check: The molecular formula corresponding to NH2CONHCONH2 is C2H5N3O2, which matches the well-established composition of biuret. Textbook discussions of “biuret in urea fertilizers” consistently depict this structure. Why Other Options Are Wrong: NH2CONH2 (option A) is urea, not biuret. NH3COONH3 and NH4COONH2 (options B and D) represent ammonium carbamate or related salt-like formulations, not the amide-bridged dicarbonyl. Option E is not the correct connectivity for biuret and misplaces the amide linkage. Common Pitfalls: Confusing ammonium carbamate (an intermediate in urea manufacture) with biuret, or assuming biuret is simply “double urea” without the bridging –NH–. Also, some learners forget that biuret forms by loss of ammonia from urea under heat. Final Answer: NH2CONHCONH2

Question 8

Calcium ammonium nitrate (CAN): approximately what percentage of nitrogen (by mass) does typical commercial CAN fertilizer contain?

Accepted Answer

Introduction / Context: Calcium ammonium nitrate (CAN) is a widely used granular nitrogen fertilizer. It is valued for safer handling than pure ammonium nitrate, reduced hygroscopicity, and a mixture of nitrate and ammoniacal nitrogen forms. Farmers and agronomists often need a quick estimate of its nitrogen content for application rate calculations. Given Data / Assumptions: Commercial CAN typically contains roughly 26–27% total nitrogen, often rounded in exam contexts to “about 25%”. The product is a mixture of ammonium nitrate with calcium carbonate or dolomite. Question asks for an approximate percentage, not an exact plant specification. Concept / Approach: Because CAN is diluted ammonium nitrate (by admixture with a calcium source), its nitrogen percentage is lower than that of pure ammonium nitrate (~34% N) and much lower than urea (46% N). Many standard references and competitive exam syllabi treat CAN as “about a quarter nitrogen,” i.e., near 25%. Step-by-Step Solution: Recall typical grade labeling: CAN ≈ 26–27% N.The answer choices are coarse; select the nearest standard benchmark.Among 10, 25, 50, and 80, the only realistic approximate value for CAN is 25. Verification / Alternative check: Fertilizer handbooks list CAN in the mid-20% nitrogen range, reflecting the stabilizing filler fraction of calcium salts that reduce nitrogen concentration compared with neat ammonium nitrate. Why Other Options Are Wrong: 10% (too low for CAN), 50% and 80% (far too high, even above urea), and 32% (closer to ammonium nitrate grades rather than CAN) do not match standard CAN specifications. Common Pitfalls: Confusing CAN with ammonium nitrate (higher N) or with urea (much higher N). Also, assuming every bag is exactly the same percentage; minor variation exists by manufacturer, but “about 25%” remains the accepted exam value. Final Answer: 25

Question 9

Triple superphosphate (TSP) manufacture: phosphate rock is acidulated using which mineral acid to produce TSP fertilizer?

Accepted Answer

Introduction / Context: Phosphate fertilizers are produced by reacting phosphate rock (apatite) with acids to render phosphorus water-soluble and plant-available. Triple superphosphate (TSP), a high-analysis product, differs from single superphosphate (SSP) in both acid used and final P2O5 content. Given Data / Assumptions: Phosphate rock is mainly fluorapatite. Goal: obtain a concentrated, water-soluble phosphate fertilizer (TSP). Industrial practice distinguishes SSP vs. TSP by choice of acid and resulting composition. Concept / Approach: SSP is produced by treating rock phosphate with sulphuric acid, generating monocalcium phosphate and gypsum (CaSO4·2H2O) as by-product. TSP, by contrast, is made by acidulating rock with phosphoric acid, avoiding gypsum formation and yielding a higher P2O5 content (~46% P2O5 in TSP). Thus, the acid that specifically identifies TSP manufacture is phosphoric acid. Step-by-Step Solution: Identify the product: TSP (triple superphosphate).Recall the process: rock phosphate + phosphoric acid → monocalcium phosphate without gypsum dilution.Therefore, select “Phosphoric acid”. Verification / Alternative check: Process descriptions in fertilizer technology texts consistently cite phosphoric acid for TSP and sulphuric acid for SSP, explaining the different by-products and analysis levels. Why Other Options Are Wrong: Nitric acid is used in nitrophosphate processes; sulphuric acid corresponds to SSP; hydrochloric/acetic acids are not used industrially for TSP manufacture. Common Pitfalls: Mixing up SSP and TSP chemistry; remembering “triple” corresponds to using phosphoric acid and getting higher grade. Final Answer: Phosphoric acid

Question 10

Identify the condensed formula: H4P2O7 corresponds to which form of phosphoric acid?

Accepted Answer

Introduction / Context: Phosphoric acids can polymerize or condense, producing a family that includes ortho-, pyro- (di-), and meta- acids. Recognizing the empirical formula helps in identifying the correct member, which is commonly referenced in phosphate processing and fertilizer chemistry. Given Data / Assumptions: The formula provided is H4P2O7. We compare it to typical forms: H3PO4 (ortho), (HPO3)n (meta), and H4P2O7 (pyro). No structural drawing tools are used; identification is by formula pattern. Concept / Approach: Pyrophosphoric (diphosphoric) acid results from the condensation of two molecules of orthophosphoric acid with loss of one molecule of water: 2 H3PO4 → H4P2O7 + H2O. Thus, the characteristic formula H4P2O7 uniquely points to the “pyro” species among common phosphoric acids. Step-by-Step Solution: Recall: orthophosphoric acid is H3PO4.Condense two orthos: 2 H3PO4 → H4P2O7 + H2O.Therefore, H4P2O7 is pyrophosphoric acid. Verification / Alternative check: Textbook tables list H3PO4 (ortho), H4P2O7 (pyro), and (HPO3)n (meta). The given formula matches the pyro entry exactly. Why Other Options Are Wrong: Orthophosphoric acid would be H3PO4; metaphosphoric acid is typically represented as a linear or cyclic polymer, (HPO3)n; “perphosphoric acid” is not a standard acid form used in fertilizer practice. Common Pitfalls: Confusing “pyro” with “meta”—remember that meta has the repeating HPO3 unit, whereas pyro has H4P2O7 from dehydrating two orthos. Final Answer: Pyrophosphoric acid

Question 11

Rock phosphate used in fertilizer manufacture is composed predominantly of which mineral species?

Accepted Answer

Introduction / Context: Rock phosphate is the essential raw material for phosphatic fertilizers. Its mineralogy determines acid consumption, impurities, and downstream processing behavior. Recognizing the dominant mineral phase is basic to fertilizer technology. Given Data / Assumptions: Typical sedimentary or igneous phosphate ores are processed. Industrial acidulation targets the apatite lattice. We select the principal mineral, not minor phases. Concept / Approach: Most rock phosphate deposits contain apatite-group minerals, especially fluorapatite with idealized composition Ca5(PO4)3F (often written Ca10(PO4)6F2 for the full unit). During acidulation (with sulphuric or phosphoric acid), the phosphate units are converted to water-soluble forms while fluorine may end up in by-products or emitted as HF unless scrubbed. Step-by-Step Solution: Identify common apatite: fluorapatite is prevalent in fertilizers-grade rock.Dicalcium and monocalcium phosphate are processed products, not major constituents of raw ore.Diammonium phosphate is a manufactured fertilizer, not a natural mineral in rock phosphate. Verification / Alternative check: Ore characterization studies for fertilizer plants routinely report fluorapatite as the main P-bearing phase, with varying carbonate substitution and accessory minerals (silica, clays, carbonates). Hydroxyapatite can occur but fluorapatite predominates in many deposits. Why Other Options Are Wrong: DCP and MCP form during processing; DAP is a finished product from ammonia and phosphoric acid; “hydroxyapatite only” is too restrictive. Common Pitfalls: Equating fertilizer product names with natural ore minerals; keep raw materials and manufactured products distinct. Final Answer: Fluorapatite

Question 12

Urea fertilizer analysis: approximately what percentage of nitrogen does standard agricultural urea contain?

Accepted Answer

Introduction / Context: Urea is the most commonly used solid nitrogen fertilizer worldwide due to its high analysis, favorable cost per unit N, and ease of handling. Knowing its nitrogen percentage is essential for calculating application rates and comparing with other N sources like ammonium sulphate or CAN. Given Data / Assumptions: The question asks for the typical N content of standard prilled or granular urea. No coated or specialty formulations are implied. Mass percentages are rounded to whole numbers for field calculations. Concept / Approach: The chemical formula of urea is CO(NH2)2. Its theoretical nitrogen content is approximately 46% by mass, which is widely cited on product labels. This high analysis reduces transportation and application costs per kilogram of nitrogen delivered to the field. Step-by-Step Solution: Compute quickly from formula: urea has two nitrogen atoms per molecule.Theoretical composition yields ~46% N by mass.Therefore, choose 46 as the standard fertilizer analysis value. Verification / Alternative check: Standard fertilizer handbooks and bag labels report “46-0-0” (N-P2O5-K2O), confirming 46% nitrogen content for conventional urea. Why Other Options Are Wrong: 10% and 28% are far below urea’s analysis; 80% and 94% are chemically impossible for this compound. Common Pitfalls: Confusing urea with ammonium nitrate (≈34% N) or CAN (~25–27% N), or forgetting that coatings (e.g., sulfur-coated urea) slightly reduce the net N percentage but the base product remains 46% N. Final Answer: 46

Question 13

Rice (paddy) agronomy: which fertilizer is generally most suitable for flooded paddy fields, considering nitrogen form and soil conditions?

Accepted Answer

Introduction / Context: Paddy (rice) is typically grown under flooded or waterlogged conditions that create anaerobic, reducing soils. The choice of nitrogen fertilizer affects losses (volatilization, denitrification) and plant availability. Among common N sources, the ammonium form is favored under submerged conditions. Given Data / Assumptions: Fields are flooded; soil is reducing with limited oxygen. Farmers seek to minimize nitrogen losses and ensure uptake. Comparison is among typical straight fertilizers. Concept / Approach: In flooded soils, ammonium (NH4+) is stable and less prone to immediate losses than nitrate, which can denitrify to N2/N2O under anaerobic conditions. Urea rapidly hydrolyzes to ammonium but is susceptible to ammonia volatilization at the surface if not incorporated. Ammonium sulphate directly supplies NH4+ and adds sulphur, often benefiting rice nutrition. Therefore, ammonium sulphate is classically regarded as most suitable for paddy among the given choices. Step-by-Step Solution: Identify soil condition: flooded, reducing—favor ammonium over nitrate.Compare N sources: ammonium sulphate supplies NH4+ directly; urea needs hydrolysis and can volatilize if surface-applied.Select ammonium sulphate as the preferred fertilizer for paddy fields. Verification / Alternative check: Rice agronomy texts often recommend ammonium-based fertilizers or deep placement of urea briquettes to reduce losses; the straightforward answer in MCQs is ammonium sulphate. Why Other Options Are Wrong: Urea is widely used but loss-prone without proper management; superphosphate is a P source, not N; potassium nitrate supplies nitrate-N, which is less suitable in flooded soils; diammonium phosphate is a P + N source used for basal P rather than the main N program. Common Pitfalls: Assuming “common use” equals “most suitable”; management practices can make urea effective, but the conceptual best match under flooding is ammonium sulphate. Final Answer: Ammonium sulphate

Question 14

Historical processes: the Montecatini process (named after the Italian chemical group) is associated with the industrial manufacture of which fertilizer/chemical?

Accepted Answer

Introduction / Context: Several named processes in fertilizer technology are linked to specific companies or countries, reflecting early innovations in large-scale production. Recognizing these associations helps with exam-style identification questions and gives historical context for today’s licensor technologies. Given Data / Assumptions: “Montecatini” refers to an Italian chemical enterprise historically involved in nitrogen processes. Question format expects a one-to-one association. Modern licensors (e.g., Stamicarbon, Snamprogetti) evolved later, but early processes bore company names. Concept / Approach: Urea is produced industrially by reacting ammonia with carbon dioxide to form ammonium carbamate and then dehydrating it to urea. Early European developers, including Montecatini, contributed process variants and plant designs that became stepping stones toward later, widely licensed technologies. Hence, the Montecatini process is historically linked to urea manufacture rather than to nitric or phosphoric acid lines, and not to CAN finishing operations. Step-by-Step Solution: Identify the company-process association in fertilizer history.Recall that Montecatini’s developments are cited with urea production routes.Select “Urea” as the matching product. Verification / Alternative check: Legacy references in fertilizer technology map Montecatini to urea manufacture, distinct from, for example, the Ostwald process (nitric acid) or wet-process phosphoric acid routes. Why Other Options Are Wrong: Nitric acid is famously the Ostwald process; phosphoric acid is produced by wet/thermal processes; CAN is a mixed fertilizer finished from ammonium nitrate and limestone/dolomite. Common Pitfalls: Confusing Italian licensors (e.g., Snamprogetti) with Montecatini; while multiple Italian entities contributed to urea technology, the exam association for Montecatini points to urea. Final Answer: Urea

Question 15

Coal-based fertilizer complexes at Ramagundam (Telangana) and Talcher (Odisha): which statement best describes how coal is utilized there?

Accepted Answer

Introduction / Context: Ammonia—the building block for urea and many nitrogen fertilizers—requires hydrogen. While most modern plants derive hydrogen by steam reforming of natural gas (methane), coal-based complexes use coal gasification to make synthesis gas (CO and H2), which is then shifted and purified for ammonia synthesis. Given Data / Assumptions: Locations: Ramagundam and Talcher in India are known for coal-based ammonia–urea projects. Coal is an alternative feedstock to natural gas for H2 production. The question asks about the principal chemical role of coal in such plants. Concept / Approach: Coal gasification converts coal into syngas. After water–gas shift (CO + H2O → CO2 + H2) and CO2 removal, the resulting hydrogen is combined with nitrogen (from air separation) in the Haber–Bosch loop to make ammonia, subsequently used to produce urea. Thus, coal is not a mere fuel or filler; it is a chemical feedstock for hydrogen generation. Step-by-Step Solution: Coal → Gasification → CO + H2.Shift reaction converts CO to additional H2 with CO2 by-product.Purified H2 + N2 → ammonia → downstream fertilizers such as urea. Verification / Alternative check: Process flow diagrams of coal-based ammonia plants show gasifiers, shift reactors, CO2 removal, and ammonia synthesis loops, confirming coal’s role as a hydrogen source. Why Other Options Are Wrong: Using coal solely as heat (A) misses the core chemistry; fillers/conditioners (C/D) are not standard; coal is not a potash source (E). Common Pitfalls: Assuming all ammonia plants are gas-based; coal and even heavy oil residues have also been used historically where natural gas is scarce. Final Answer: Coal is gasified to obtain hydrogen-rich synthesis gas (coal gas) for ammonia/urea

Question 16

Haber–Bosch ammonia catalyst: which substance is classically used as a promoter for the iron-based ammonia synthesis catalyst?

Accepted Answer

Introduction / Context: Industrial ammonia synthesis typically employs magnetite-derived iron catalysts. To achieve high activity and stability under demanding conditions (high pressure, moderate-to-high temperature, hydrogen-rich gas), promoters are added. Knowing the difference between electronic and structural promoters is a common exam topic in chemical/fertilizer technology. Given Data / Assumptions: Base catalyst: iron (Fe) derived from Fe3O4 (magnetite). Promoters can be electronic (altering adsorption characteristics) or structural (enhancing surface area and sintering resistance). Single best answer is requested. Concept / Approach: Potassium oxide (K2O) is a classical electronic promoter for the iron catalyst, improving nitrogen adsorption/activation by modifying the electronic environment of the Fe surface. Other common additives include Al2O3 and CaO as structural promoters that help maintain pore structure and limit sintering. Noble metals like Pt or base metals like Ni are not standard promoters for the traditional iron system (Ni is instead used for methanation or steam reforming catalysts). Step-by-Step Solution: Identify the classic promoter set for Fe-based NH3 synthesis.Electronic promoter: K2O → enhances surface properties for N2 activation.Therefore, select K2O as the correct answer. Verification / Alternative check: Standard catalyst compositions list Fe with K2O (electronic) and Al2O3/CaO (structural). This division appears in most ammonia technology references. Why Other Options Are Wrong: Pt and Ni are not used as promoters in the conventional Fe Haber–Bosch catalyst; Al2O3 is a promoter but is typically categorized as structural rather than the classic single “promoter” sought in such MCQs; CuO is associated with low-temperature shift catalysts, not NH3 synthesis. Common Pitfalls: Thinking “any oxide additive” is interchangeable; promoter roles are distinct. Also, mixing up NH3 catalyst formulation with reforming/shift/methanation catalysts elsewhere in the ammonia–urea complex. Final Answer: K2O

Question 17

In industrial phosphorus chemistry, what product is predominantly formed when orthophosphoric acid (H3PO4) is strongly heated to about 900 °C under dehydrating conditions?

Accepted Answer

Introduction / Context: Phosphoric acids undergo stepwise dehydration on heating. Understanding which condensed phosphate forms at elevated temperature is essential in fertilizer manufacture and inorganic chemistry. This question focuses on the thermal transformation of orthophosphoric acid (H3PO4) at very high temperature, around 900 °C, where extensive dehydration occurs. Given Data / Assumptions: Feed: orthophosphoric acid (H3PO4). Strong heating near 900 °C with no special catalysts mentioned. Dehydration (loss of water) is the dominant process under these conditions. Concept / Approach: Orthophosphoric acid first condenses to pyrophosphoric acid (H4P2O7) on moderate heating by eliminating water. With further heating and deeper dehydration, cyclic or polymeric metaphosphoric acids (general formula HPO3)n form. At still higher severities, phosphorus pentoxide (P2O5) may be present as a volatilized species, but the recognized condensed phase product of strong dehydration of H3PO4 is metaphosphoric acid. Step-by-Step Solution: Start: H3PO4 (orthophosphoric acid).Moderate heat: 2 H3PO4 → H4P2O7 + H2O (pyrophosphoric acid).Strong heat (≈ 900 °C): extensive dehydration → (HPO3)n (metaphosphoric acid).Therefore, the principal product at the stated temperature is metaphosphoric acid. Verification / Alternative check: Textbook dehydration sequences list orthophosphoric → pyrophosphoric → metaphosphoric with increasing temperature. Industrial drying and calcination steps exploit these equilibria to target specific phosphate species. Why Other Options Are Wrong: Pyrophosphoric acid: forms at lower temperatures; further heating continues dehydration. No change: contradicted by well-known dehydration behavior. None of these / phosphorus pentoxide only: while P2O5 can appear at very high severities, the recognized condensed product of heating H3PO4 is metaphosphoric acid. Common Pitfalls: Confusing the first step (pyro formation) with the ultimate high-temperature product; overlooking that “metaphosphoric acid” represents cyclic/polymeric species. Final Answer: Metaphosphoric acid

Question 18

Hydrogen sourcing for nitrogenous fertilisers: Which routes are commercially used to produce H2 feed for ammonia/urea plants?

Accepted Answer

Introduction / Context: Ammonia synthesis (Haber–Bosch) requires a reliable hydrogen source. Fertiliser complexes therefore adopt hydrogen-generation technologies suited to local feedstock availability, energy economics, and scale. This question asks which listed routes are used commercially to supply hydrogen to nitrogenous fertiliser plants. Given Data / Assumptions: We consider proven industrial routes, not laboratory curiosities. Plants may be integrated with refineries, steelworks, or stand-alone utilities. Regional economics decide which option dominates in a country. Concept / Approach: Steam reforming of light hydrocarbons (natural gas, naphtha) is the global workhorse, yielding syngas (H2 + CO/CO2) followed by shift and CO2 removal. Electrolysis of water is also used, particularly where low-cost power is available or for small/remote units. Coke-oven and other off-gases can be cryogenically or chemically separated to recover hydrogen. Hence, all three listed routes are used commercially in various contexts. Step-by-Step Solution: Identify mainstream method: steam reforming of NG/naphtha.Recognize alternative but commercial routes: water electrolysis; H2 recovery from coke-oven gas.Because each is practiced, select the inclusive option.Therefore, “All of the above” is correct. Verification / Alternative check: Plant surveys show dominant adoption of steam reforming, with electrolyzers used in power-rich regions and H2 recovery units in integrated steel–chemicals sites. Why Other Options Are Wrong: Each single-route answer omits other commercially used routes. “Coal gasification only” ignores widespread reforming and electrolysis deployments. Common Pitfalls: Assuming there is only one “right” technology globally; in practice, feedstock economics and emissions policy drive diverse choices. Final Answer: All of the above

Question 19

Coal-based ammonia complexes: Which gasifier type is most characteristically attached to coal-based fertiliser (ammonia) plants to generate pressurised synthesis gas?

Accepted Answer

Introduction / Context: Coal-based fertiliser plants require synthesis gas (H2, CO, CO2) suitable for shift conversion and subsequent ammonia synthesis. The choice of gasifier affects pressure level, gas composition, tar handling, and downstream compression costs. This item targets recognition of the gasifier historically associated with coal-to-ammonia complexes. Given Data / Assumptions: Objective: produce syngas for shift and H2 recovery at conditions compatible with large downstream compressors. Coal feed; reliability and ash handling are important. Traditional installations valued pressurised output to reduce compression duty. Concept / Approach: The Lurgi fixed-bed gasifier operates at elevated pressure and has long been paired with ammonia plants, easing integration by delivering gas at useful pressure. By contrast, the Kopper–Totzek (entrained-flow) process runs near atmospheric pressure and would require substantial downstream compression, which was historically less attractive in fertiliser service despite other merits (tar minimisation, high throughput). Thus, the characteristic choice is the Lurgi high-pressure design. Step-by-Step Solution: List candidate gasifiers and their pressure regimes.Match fertiliser plant needs: higher-pressure gas preferred.Identify Lurgi as the archetypal pressurised option.Select Lurgi high-pressure fixed-bed gasifier as correct. Verification / Alternative check: Historical coal-to-ammonia complexes cite Lurgi-type units upstream of shift/CO2 removal, evidencing the pairing. Why Other Options Are Wrong: Kopper–Totzek is atmospheric; compression penalty is large. Answers specifying only a pressure (20 or 40 atm) ignore reactor type and are incomplete. Fluidised-bed “without compression needs” is unrealistic; compression is still required for ammonia synthesis. Common Pitfalls: Equating gasifier choice solely with ash/slag handling; for fertiliser integration, delivery pressure is also pivotal. Final Answer: Lurgi high-pressure fixed-bed gasifier

Question 20

Acidulation of phosphate rock: When calcium fluorapatite (phosphate rock) is treated with sulphuric acid under typical fertiliser conditions, what product is obtained?

Accepted Answer

Introduction / Context: Manufacture of phosphate fertilisers begins by acidulating phosphate rock (chiefly calcium fluorapatite) with an acid. The choice of acid and its concentration determine whether the output is superphosphate, triple superphosphate, or phosphoric acid. The question asks for the product formed with sulphuric acid under standard single-superphosphate conditions. Given Data / Assumptions: Reactant: calcium fluorapatite (phosphate rock). Acid: sulphuric acid (dilute to moderate strength for SSP). Conventional fertiliser process (wet acidulation), not pure phosphoric acid route. Concept / Approach: Reacting phosphate rock with sulphuric acid forms monocalcium phosphate monohydrate (the plant-available P component of SSP) and gypsum (CaSO4·2H2O) as a by-product. When phosphoric acid (not sulphuric) is used, triple superphosphate results. Wet-process phosphoric acid is made by digesting rock with excess sulphuric acid and separating gypsum; this is a different flowsheet. Step-by-Step Solution: Identify reagents: Ca5(PO4)3F and H2SO4.Recall SSP reaction: → Ca(H2PO4)2·H2O + CaSO4·2H2O (gypsum).Associate this product mixture with “simple superphosphate”.Therefore, with sulphuric acid under SSP conditions, the product is simple superphosphate. Verification / Alternative check: Process descriptions label SSP as rock + H2SO4; TSP as rock + H3PO4; wet-process H3PO4 requires filtration to remove gypsum. Why Other Options Are Wrong: Orthophosphoric acid only: that is the wet-process acid route, not directly SSP. Triple superphosphate: requires phosphoric acid, not sulphuric. Red phosphorus: unrelated to wet acidulation. Dicalcium phosphate only: not the standard SSP product mixture. Common Pitfalls: Confusing the SSP (H2SO4) and TSP (H3PO4) flowsheets; forgetting gypsum is inevitably co-produced in SSP. Final Answer: Simple superphosphate (single superphosphate)

Fertiliser Technology Questions