Question 1

Crop nutrition timing: Which fertilizer class is most suitable for accelerating seed set and fruit formation during the later stages of plant growth?

Accepted Answer

Introduction / Context: Plants require balanced nutrition through their lifecycle. Nitrogen drives early vegetative growth; phosphorus supports energy transfer, root growth, flowering, and fruit/seed development; potassium improves stress tolerance, quality, and stem strength. Understanding which nutrient class most directly influences flowering and seed/fruit formation helps optimize topdressing programs and yield outcomes. Given Data / Assumptions: Stage of interest: reproductive phase—flowering, pollination, seed set, fruit formation. Goal: accelerate or promote reproductive development, not early foliage growth. Balanced fertility of other nutrients is assumed adequate. Concept / Approach: Phosphorus plays a central role in ATP/ADP energy metabolism and is strongly linked to flowering and seed/fruit development. Adequate phosphatic fertilization ensures sufficient energy and biochemical support for reproductive processes. Nitrogen remains important, but excessive late N can prolong vegetative growth at the expense of reproductive development. Potassium enhances fruit quality and disease tolerance but is not the principal accelerator of flowering/seed set compared with phosphorus. Step-by-Step Solution: Align nutrient function with growth stage: reproductive → phosphorus emphasis.Avoid over-emphasis on nitrogen late in the season to prevent lush vegetative growth.Recognize potassium’s role in quality and stress response rather than initiating reproductive events.Select “phosphatic fertilizer.” Verification / Alternative check: Agronomic guides consistently recommend sufficient P availability before and through flowering to ensure successful seed/fruit formation. Tissue tests and soil P indices are monitored to avoid P limitation at this stage. Why Other Options Are Wrong: Nitrogenous: primarily drives foliage; excessive N can delay flowering.Potassic: improves quality and strength but is not the main accelerator of fruit set.None of these: incorrect because phosphatic fertilizers directly support reproductive processes. Common Pitfalls: Assuming late heavy N always boosts yield; it can reduce fruiting. Ignoring that P must be available in the root zone well before flowering for best effect. Final Answer: Phosphatic fertilizer

Question 2

Triple superphosphate (≈46% P2O5) production: Phosphate rock is reacted with orthophosphoric acid of approximately what concentration (by mass percent H3PO4) to make TSP?

Accepted Answer

Introduction / Context: Triple superphosphate (TSP) is a high-analysis phosphate fertilizer produced by digesting phosphate rock with concentrated orthophosphoric acid rather than sulfuric acid. The acid strength used strongly influences reaction kinetics, product grade, and granulation behavior. Recognizing the approximate acid concentration is a standard fertilizer technology question. Given Data / Assumptions: TSP product analysis: about 46% P2O5. Reagent: orthophosphoric acid (H3PO4) of high concentration. We are asked for H3PO4 wt% range, not P2O5 equivalent. Concept / Approach: Manufacture of TSP typically employs orthophosphoric acid around 70–80 wt% H3PO4 to ensure rapid conversion and produce high-grade mono-calcium phosphate within each granule. Using too dilute acid lengthens reaction time and yields lower-grade products, while ultra-concentrated acid near 100% is impractical and hazardous for routine plant operation. Hence, a practical range of roughly 75–80% H3PO4 is the accepted textbook answer. Step-by-Step Solution: Identify target product grade (≈46% P2O5) requiring concentrated acid attack.Recall industry practice: use ≈70–80% H3PO4 for efficient rock digestion.Match to the closest range among choices: 75–80.Select “75–80.” Verification / Alternative check: Design manuals and plant experience indicate orthophosphoric acid in the mid-70% range for robust TSP granulation and quality control. Why Other Options Are Wrong: 25–28 or 52–54: too dilute for making high-grade TSP efficiently.>98: near pure H3PO4, impractical and unnecessary for standard TSP production. Common Pitfalls: Confusing H3PO4 wt% with P2O5 wt%; both are used in literature but are not interchangeable numerically. Final Answer: 75–80

Question 3

When phosphate rock is treated with nitric acid (often with associated sulfuric acid steps in some flowsheets), the resulting fertilizer product is classified as:

Accepted Answer

Introduction / Context: Nitrophosphate processes, such as the Odda route, digest phosphate rock with nitric acid to produce a solution containing calcium nitrate and phosphoric species, which is then further processed to yield N–P or N–P–K fertilizers. Some variants introduce sulfuric acid for calcium removal steps, but the defining acidulation is with nitric acid. Knowing the correct product classification distinguishes nitrophosphate chemistry from sulfuric-acid superphosphates and ammoniated phosphates. Given Data / Assumptions: Starting material: phosphate rock. Main acidulant: nitric acid (HNO3), possibly with auxiliary steps involving H2SO4. Product family: fertilizers that contain nitrogen and phosphorus together. Concept / Approach: Reaction of phosphate rock with nitric acid yields a mixed nutrient liquor that, after neutralization and finishing, gives nitrophosphate. This is a complex fertilizer where N and P are present within the same granule matrix. Diammonium phosphate (DAP) instead results from ammoniating phosphoric acid, not nitric acid. Tricresyl phosphate and tributyl phosphate are organic esters, used as plasticizers or extractants, not bulk fertilizers. Step-by-Step Solution: Identify acidulant as HNO3 → characteristic of nitrophosphate route.Recognize combined N and P in final product → complex fertilizer.Exclude DAP (comes from NH3 + H3PO4) and organic phosphates (non-fertilizer chemicals).Select “Nitrophosphate.” Verification / Alternative check: Industry references list nitrophosphate products under trade names produced by nitric acid digestion followed by controlled neutralization and granulation steps. Why Other Options Are Wrong: Diammonium phosphate: manufactured from phosphoric acid and ammonia, not nitric acid digestion of rock.Tricresyl/tributyl phosphates: organic chemicals, not fertilizers. Common Pitfalls: Confusing nitrophosphate (HNO3 route) with superphosphates (H2SO4 route) and with ammoniated phosphates (H3PO4 + NH3). Final Answer: Nitrophosphate

Question 4

Process thermochemistry: The neutralization of nitric acid by ammonia to form ammonium nitrate (NH4NO3) is best described as what type of reaction?

Accepted Answer

Introduction / Context: Ammonium nitrate manufacture involves neutralizing nitric acid with ammonia to form an aqueous melt, which is then concentrated and solidified. Correctly identifying the thermic nature of the neutralization is essential for safe reactor design, heat recovery, and preventing runaway conditions, especially given the energetic nature of ammonium nitrate at high temperatures. Given Data / Assumptions: Reactants: NH3 (typically gaseous) and HNO3 (aqueous). Product: NH4NO3 in solution; large heat release on neutralization. Industrial neutralizers incorporate heat removal. Concept / Approach: Acid–base neutralization reactions generally release heat. The specific reaction NH3 + HNO3 → NH4NO3 is strongly exothermic, and plants capture this heat in process water or generate low-pressure steam. The exothermicity is central to temperature control in neutralizers to avoid decomposition or undesirable side reactions in later steps. Step-by-Step Solution: Recognize acid–base neutralization → heat is released.Apply to NH3 + HNO3 → NH4NO3 with substantial enthalpy of neutralization.Therefore classify as “exothermic.”Design implication: incorporate cooling/heat recovery in neutralizer system. Verification / Alternative check: Plant heat balances show neutralizer duty recovered as hot process condensate or steam; operating manuals warn against inadequate cooling capacity. Why Other Options Are Wrong: Catalytic/autocatalytic: no catalyst is required for the neutralization step.Endothermic: contradicts measured heats of neutralization and plant practice. Common Pitfalls: Underestimating heat release, leading to temperature spikes that complicate downstream evaporation and increase safety risks. Final Answer: Exothermic

Question 5

In the “dual process” variant of soda-ash manufacture (integrated with ammonia recovery), which fertilizer by-product is produced?

Accepted Answer

Introduction / Context: The Solvay (soda-ash) process uses brine and ammonia with carbon dioxide to produce sodium carbonate. In the “dual process,” integration with ammonium chloride crystallization allows recovery of a fertilizer co-product, improving overall economics and reducing waste brine issues. Recognizing the specific fertilizer by-product is a classic chemical technology question. Given Data / Assumptions: Inputs: NaCl brine, NH3, CO2. Main product: Na2CO3 (soda ash). Variant: dual process recovers a marketable ammonium salt. Concept / Approach: In Solvay chemistry, CO2 reacts with ammonia and brine to form ammonium bicarbonate, which precipitates sodium bicarbonate; upon calcination this yields soda ash. The ammonium chloride remaining in mother liquor can be recovered as a commercial fertilizer in the dual process. Thus, ammonium chloride (NH4Cl) is the fertilizer co-product. Ammonium sulfate or nitrate are not generated by the standard Solvay routes. Step-by-Step Solution: Recall key Solvay steps yielding NaHCO3 solid and NH4Cl in solution.In the dual process, crystallize and recover NH4Cl as fertilizer grade.Match by-product to options: “Ammonium chloride.”Exclude sulphate/nitrate—require different acid sources not present here. Verification / Alternative check: Process summaries and flowsheets label the dual process as soda ash + ammonium chloride co-production, especially in regions with NH4Cl fertilizer demand. Why Other Options Are Wrong: Ammonium sulphate/nitrate: not formed in carbonate/chloride Solvay chemistry.None of these: incorrect because NH4Cl is indeed produced and marketed. Common Pitfalls: Confusing spent liquor disposal in classic Solvay with the integrated dual process that valorizes NH4Cl. Final Answer: Ammonium chloride

Question 6

Location question (India): Which fertilizer plant is noted for sourcing part of its hydrogen requirement from coke-oven gas?

Accepted Answer

Introduction / Context: Hydrogen sources for ammonia vary by local infrastructure. In integrated steel-fertilizer complexes, coke-oven gas from steel operations can be a valuable hydrogen-rich stream. Historically in India, Rourkela—associated with the Steel Authority of India Limited (SAIL)—is recognized for utilizing coke-oven gas to supplement hydrogen for fertilizer production. Given Data / Assumptions: We are asked to identify the plant location known for using coke-oven gas as a hydrogen source. Options include multiple Indian fertilizer/industrial sites under different organizations. Historical context: integration between steelworks and ammonia units. Concept / Approach: Coke-oven gas contains a significant fraction of hydrogen formed during coal carbonization. Where a steel plant and a fertilizer unit are co-located or integrated, it is economical to recover and purify H2 from this stream. Rourkela’s steel complex provided such an opportunity, making it the best-known example in the options listed. Step-by-Step Solution: Associate coke-oven gas hydrogen recovery with an integrated steel site.Identify Rourkela as the steel hub under SAIL among the options.Select “Rourkela (under SAIL).”Recognize others (Barauni, Nangal, Talcher) follow different feedstock histories. Verification / Alternative check: Historical notes and training manuals cite Rourkela’s practice of H2 recovery from coke-oven gas for ammonia/fertilizer purposes. Why Other Options Are Wrong: Barauni/Nangal/Talcher: not the canonical examples for coke-oven gas hydrogen utilization. Common Pitfalls: Assuming all steel towns supplied hydrogen to fertilizer units; integration depended on specific plant histories and logistics. Final Answer: Rourkela (under SAIL)

Question 7

In plant physiology and agronomy, “plant tranquillisers” (growth retardants) are chemicals that primarily ________ to manage canopy architecture and lodging risk.

Accepted Answer

Introduction / Context: Plant tranquillisers, more commonly called plant growth retardants or anti-gibberellins, are applied to limit excessive vegetative growth without severely affecting photosynthesis or reproductive development. They are widely used to manage crop stature, reduce lodging, and improve harvest index. Understanding their primary effect helps agronomists select the right regulator for canopy management and yield stability. Given Data / Assumptions: The term refers to growth-retarding regulators such as chlormequat chloride (CCC), mepiquat chloride, daminozide, and maleic hydrazide. Typical target tissues are rapidly elongating stems and internodes. The question seeks the chief agronomic outcome rather than all secondary effects. Concept / Approach: Many tranquillisers act by interfering with the biosynthesis or action of gibberellins, hormones that promote stem elongation and cell expansion. By moderating gibberellin pathways, they reduce internode length, producing shorter, sturdier plants that resist lodging in cereals and fiber crops. This height control is the signature purpose of “plant tranquillisers.” Step-by-Step Solution: Identify the hormone pathway targeted: gibberellin synthesis/action.Link mechanism to morphology: reduced gibberellin effect → reduced internode elongation.Translate to agronomic outcome: shorter, compact canopy; improved standability; easier harvest.Therefore, the primary role is holding back stem growth at a desired height. Verification / Alternative check: Standard agronomy texts show that CCC in wheat or mepiquat in cotton reduces plant height and lodging. While some regulators can secondarily influence maturation timing, the hallmark agronomic reason to apply tranquillisers is height control and lodging reduction. Why Other Options Are Wrong: “Cause early maturation” is not the principal and consistent outcome across crops. “Accelerate ripening” is typically linked to ethylene-releasing compounds, not growth retardants. “Produce seedless fruit” describes parthenocarpy regulated by other hormones. “Stimulate apical dominance” contradicts the height-reduction intent. Common Pitfalls: Confusing growth retardants with ripening regulators or auxin/ethylene products. Also assuming that any regulator “boosts yield”; tranquillisers primarily reshape canopy and reduce lodging risk, which may only indirectly benefit yield. Final Answer: hold back stem elongation and maintain plants at a desired height

Question 8

Ostwald process performance: During nitric acid manufacture, catalytic oxidation of ammonia over platinum at about 800 °C converts NH3 to NO with approximately what percent conversion?

Accepted Answer

Introduction / Context: The Ostwald process converts ammonia to nitric oxide (NO) over platinum–rhodium gauze at high temperature, followed by oxidation to NO2 and absorption to form HNO3. The initial converter performance is a key plant KPI, typically measured as the single-pass conversion of NH3 to NO under steady state. Knowing the characteristic conversion helps diagnose catalyst health and operating conditions. Given Data / Assumptions: Operating temperature near 800–900 °C. Platinum-group metal gauze catalyst. Well-mixed feed with the proper NH3/O2 ratio and minimal poisons. Concept / Approach: Under optimized conditions, the oxidation of NH3 is highly selective and near-quantitative to NO at the reactor outlet. Practical plants achieve about 96–99% conversion of NH3 to NO in the first stage. The canonical exam value often cited is approximately 98% conversion, acknowledging minor side reactions (to N2 and N2O) and losses due to catalyst wear or maldistribution. Step-by-Step Solution: Recognize that NH3 oxidation is fast and exothermic over Pt–Rh gauze.Industrial converters are designed to achieve conversion in the high 90s.Select the closest standard figure from the options: 98%. Verification / Alternative check: Plant heat balances and downstream absorber loading imply high NO production; emissions controls target minor by-products (N2O). Operating manuals quote conversions approaching 98–99% on fresh, clean gauze. Why Other Options Are Wrong: 38%, 68%, and 82% are too low for modern converters and would cause severe efficiency losses. 92% is closer but still below the widely referenced benchmark in well-operated units. Common Pitfalls: Confusing conversion with selectivity; although conversion is very high, selectivity to NO vs. N2O/N2 can vary with temperature, gauze condition, and mixing. Final Answer: 98

Question 9

Fertilizer identification by analysis: A nitrogenous fertilizer analyzing about 35% nitrogen most likely corresponds to which product?

Accepted Answer

Introduction / Context: Quickly recognizing fertilizers from their typical nitrogen analysis is useful in procurement, agronomy, and exam settings. Common single-nutrient nitrogen fertilizers include urea (46% N), ammonium nitrate (~34–35% N), calcium ammonium nitrate (~25–27% N), and ammonium sulphate (~21% N). Matching an analysis to a product narrows application strategies and handling requirements. Given Data / Assumptions: Stated nitrogen content: about 35% by mass. Solid fertilizer context implied by the listed options. We assume standard commercial grades, not specialty blends. Concept / Approach: Urea is 46% N, clearly higher than 35%. CAN is in the mid-20s, and ammonium sulphate is ~21% N. Ammonium nitrate as a prilled/granular oxidizer carries approximately 34% N (some grades reported near 35%). Therefore, a fertilizer with about 35% N best matches ammonium nitrate among the listed choices. Step-by-Step Solution: Compare 35% to common benchmarks: urea 46, AN ~34–35, CAN ~25–27, AS ~21.Select the nearest standard: ammonium nitrate.Confirm that this aligns with known product properties and uses. Verification / Alternative check: Bag labels and fertilizer handbooks consistently list ammonium nitrate near 34–35% N, often expressed as 34.5% N in some markets. Why Other Options Are Wrong: Urea is too high at 46%; CAN is too low in the 20s; ammonium sulphate is ~21% N; aqua ammonia is a liquid system and is not a ~35% N solid fertilizer. Common Pitfalls: Confusing CAN with ammonium nitrate due to similar names; remembering that CAN contains limestone/dolomite diluent, lowering the N percentage. Final Answer: Ammonium nitrate

Question 10

Named reactor hardware: The Fauser–Montecatini converter is historically associated with which unit operation in a nitrogen fertilizer complex?

Accepted Answer

Introduction / Context: Legacy plant equipment often carries the names of developers or licensors. The Fauser–Montecatini converter is a classic high-pressure ammonia synthesis reactor design from early generations of Haber–Bosch technology. Recognizing which step it belongs to helps interpret historical plant diagrams and exam questions that reference vintage hardware. Given Data / Assumptions: Fauser and Montecatini were Italian innovators in ammonia technology. “Converter” in nitrogen plants generally denotes the ammonia synthesis reactor. Other units (shift, methanation, reforming) have distinct equipment names. Concept / Approach: The ammonia converter is the fixed-bed catalytic reactor where N2 and H2 produce NH3 at elevated pressure and moderate temperature, using promoted iron catalysts. The Fauser–Montecatini design relates to this synthesis step rather than upstream gas conditioning (shift or methanation) or secondary reforming, which are separate reactors with different internals and catalysts. Step-by-Step Solution: Identify the historical association: Fauser–Montecatini with ammonia synthesis.Differentiate from shift (Fe/Cr), methanation (Ni), and reforming (Ni) reactors.Select “Ammonia synthesis (high-pressure converter)”. Verification / Alternative check: Historical references to plants such as FCI Sindri cite Fauser–Montecatini high-pressure converters in the NH3 loop, confirming the association. Why Other Options Are Wrong: Methanation and shift use different catalysts and reactor styles; secondary reformers are fired reactors combining air addition with catalytic beds—distinct from the ammonia loop converter. Common Pitfalls: Assuming “converter” generically applies to any catalytic reactor; in NH3 plant jargon, it typically points to the synthesis loop reactor. Final Answer: Ammonia synthesis (high-pressure converter)

Question 11

Urea synthesis chemistry: In the industrial manufacture of urea, the immediate intermediate formed from NH3 and CO2 inside the high-pressure reactor is ________.

Accepted Answer

Introduction / Context: Urea production integrates ammonia synthesis with CO2 capture by converting these two streams to urea. The reaction proceeds via a key intermediate, knowledge of which is essential for understanding recycle loops, heat integration, and safety in urea plants. Given Data / Assumptions: Reagents: NH3 and CO2 at high pressure and elevated temperature. Closed-loop design with carbamate formation and decomposition/recovery sections. We seek the chemical intermediate formed before dehydration to urea. Concept / Approach: The first step is exothermic formation of ammonium carbamate: CO2 + 2 NH3 → NH2COONH4. The second step is endothermic dehydration of ammonium carbamate to urea and water. Ammonium carbonate is not the controlled process intermediate in modern urea synthesis; biuret and cyanuric acid are side products arising from urea condensation at elevated temperatures and are not desired intermediates. Step-by-Step Solution: NH3 + CO2 in the reactor → ammonium carbamate.Ammonium carbamate → urea + H2O by dehydration.Recycle unconverted carbamate and excess NH3 for efficiency. Verification / Alternative check: All major licensor packages (e.g., Stamicarbon, Saipem) describe the same two-step mechanism featuring ammonium carbamate as the immediate intermediate. Why Other Options Are Wrong: Ammonium carbonate is not the targeted intermediate; biuret/cyanuric acid are thermal condensation by-products and are controlled to low levels. Common Pitfalls: Confusing carbamate with carbonate or assuming biuret is part of the intended pathway; it is a quality-limiting impurity formed in finishing if overheated. Final Answer: Ammonium carbamate

Question 12

Phosphate fertilizer grading convention: Commercial phosphatic fertilizers are graded on the basis of their ________ content.

Accepted Answer

Introduction / Context: Fertilizer labeling uses standard oxide conventions—N-P2O5-K2O—to report guaranteed analyses. Even though plants absorb elemental nutrients (e.g., P as orthophosphate), industry practice expresses phosphorus in terms of P2O5 equivalent for historical and regulatory reasons. Understanding this convention is fundamental in interpreting product specs and comparing fertilizers. Given Data / Assumptions: The question concerns grading/labeling, not plant uptake chemistry. We follow standard commercial practice and legal definitions. We must choose the correct oxide equivalent used globally. Concept / Approach: Phosphatic fertilizers (e.g., single superphosphate, triple superphosphate, DAP, MAP) declare phosphorus as percent P2O5 equivalent on the bag. This does not mean the product literally contains P2O5; it is a conventional expression allowing uniform comparison across different chemical forms. Thus, “P2O5” is the correct basis for grading. Step-by-Step Solution: Identify the labeling system: N-P2O5-K2O convention.Match phosphorus term to P2O5 equivalent.Select “P2O5” as the correct answer. Verification / Alternative check: Regulatory documents and fertilizer handbooks consistently define phosphorus labeling in P2O5 terms for guaranteed analyses. Why Other Options Are Wrong: P2O3 and PCl5 are not used for fertilizer grade; H3PO4 is an acid feedstock, not the labeling basis; “PO4^3- expressed as elemental P only” does not follow the oxide convention. Common Pitfalls: Confusing agronomic phosphorus (elemental P basis) with labeling conventions; conversion factors exist to translate between P and P2O5 when needed. Final Answer: P2O5

Question 13

Macronutrient triad check: Which of the following is not necessarily a major (primary) nutrient component that must be present in every fertilizer product?

Accepted Answer

Introduction / Context: Primary macronutrients for plants are nitrogen (N), phosphorus (P), and potassium (K). Many commercial fertilizers supply one, two, or all three of these, depending on soil tests and crop needs. Sulphur (S) is an essential nutrient but is classified as a secondary macronutrient, and not all fertilizers include it by default. Given Data / Assumptions: We distinguish between “primary” (N, P, K) and “secondary/micronutrients”. The question asks which is not necessarily required in every fertilizer. Some products are straight fertilizers (e.g., urea) with only one primary nutrient. Concept / Approach: Fertilizers are tailored: a bag may be N-only (46-0-0 urea), NP (DAP 18-46-0), or NPK in various ratios. None of these necessarily includes sulphur unless specifically formulated (e.g., ammonium sulphate provides S). Therefore, sulphur is not a component that must be present in every fertilizer product, although it can be agronomically important in sulphur-deficient soils. Step-by-Step Solution: Recall the primary nutrients: N, P, K.Recognize sulphur as a secondary nutrient in labeling conventions.Conclude that sulphur is not mandatory in every fertilizer formulation. Verification / Alternative check: Common SKUs: Urea (N only), MOP (K2O only), DAP (NP), SSP (P with some S), each illustrating that sulphur is optional and product-specific. Why Other Options Are Wrong: Nitrogen, phosphorus, and potassium are the primary macronutrients considered core to fertilization programs; “All of N, P, and K must always be present” is false because single-nutrient fertilizers are widely used. Common Pitfalls: Equating “essential” with “always included”; essentiality refers to plant biology, while product composition depends on agronomic prescriptions and manufacturing. Final Answer: Sulphur

Question 14

Safety and handling of ammonium nitrate: Which statement is correct regarding fertilizer-grade ammonium nitrate and common practice before field use?

Accepted Answer

Introduction / Context: Ammonium nitrate (AN) is a valuable nitrogen source but presents handling and safety challenges. Many markets mitigate its explosive potential and caking tendency by producing calcium ammonium nitrate (CAN), a mixture of AN with ground limestone or dolomite. Understanding these properties is crucial for safe storage and regulatory compliance. Given Data / Assumptions: Fertilizer-grade AN has approximately 34–35% nitrogen, not “N2”. AN is hygroscopic, tending to absorb moisture and cake. AN can undergo explosive decomposition under certain conditions. Concept / Approach: To reduce the explosive hazard and improve physical properties, AN is often diluted with limestone/dolomite to form CAN. The inert solid diluent stabilizes the product, lowers nitrogen concentration, and reduces sensitivity. Statements denying hygroscopicity or explosive risk are incorrect and potentially dangerous. The accurate description highlights the limestone blending practice. Step-by-Step Solution: Note AN properties: hygroscopic and potentially hazardous.Identify mitigation: blend with limestone (or dolomite) → CAN.Pick the statement that matches industry practice and safety rationale. Verification / Alternative check: Fertilizer safety standards and technical sheets describe CAN as stabilized AN with reduced detonation potential and better storage behavior compared with straight AN. Why Other Options Are Wrong: “About 40% N2” misstates both value and unit; AN is hygroscopic; and it is indeed prone to explosive decomposition under misuse; blending with potash is not a universal anti-caking measure for AN. Common Pitfalls: Confusing nitrogen percentage with dioxygen/nitrogen gas notation; underestimating storage risks associated with AN. Final Answer: It is mixed with limestone powder to reduce explosive hazard before using as fertilizer (CAN)

Question 15

Commercial nitric acid production route in fertilizer complexes: Which process is used at scale to make nitric acid?

Accepted Answer

Introduction / Context: Nitric acid is a cornerstone intermediate for nitrate fertilizers and explosives. Modern fertilizer plants use the Ostwald process, which oxidizes ammonia to NO, then to NO2, followed by absorption in water to form HNO3. Recognizing the mainstream industrial route is essential for process engineers and students of fertilizer technology. Given Data / Assumptions: Large-scale, continuous production is implied. Ammonia is available on-site from Haber–Bosch synthesis. Electric arc processes are historical and energy-inefficient. Concept / Approach: The Ostwald process dominates: NH3 is catalytically oxidized over Pt–Rh gauze to NO, then further oxidized to NO2 and absorbed to HNO3. Alternative reactions such as double-decomposition of calcium nitrate with sulphuric acid are not standard large-scale nitric acid routes; electric arc nitrogen fixation is obsolete due to high power demand. Step-by-Step Solution: Identify the modern industrial method: oxidation of ammonia.Note subsequent steps: NO → NO2 → absorption to HNO3.Select the Ostwald process as the correct route. Verification / Alternative check: Process flow diagrams for all contemporary nitric acid units center on the ammonia oxidation converter and absorption tower sequence. Why Other Options Are Wrong: Calcium nitrate with sulphuric acid is not a standard HNO3 manufacturing route; electric arc processes are historical; “none” contradicts established practice; direct hydration without oxidation is incomplete. Common Pitfalls: Confusing production of nitric acid with production of nitrate salts, which may involve different reactions downstream. Final Answer: Oxidation of ammonia (Ostwald process)

Question 16

Superphosphate manufacture: Reaction of which mineral acid with phosphate rock yields superphosphate fertilizers?

Accepted Answer

Introduction / Context: Superphosphate fertilizers are produced by acidulating phosphate rock (apatite). The classical “single superphosphate” (SSP) route uses sulphuric acid, resulting in monocalcium phosphate along with gypsum as a by-product. Distinguishing this from the phosphoric-acid route for triple superphosphate (TSP) is a common exam checkpoint. Given Data / Assumptions: “Superphosphate” generally refers to SSP unless otherwise specified as TSP. Feedstock is rock phosphate rich in apatite minerals. We are to identify the acid reagent used in the standard SSP process. Concept / Approach: In SSP manufacture, phosphate rock reacts with sulphuric acid to form monocalcium phosphate in an acidic slurry while precipitating calcium sulphate (gypsum). The cured product contains water-soluble phosphate suitable for direct application. In contrast, TSP is made by reacting rock phosphate with phosphoric acid, giving a higher analysis product; thus “sulphuric acid” aligns specifically with superphosphate in the classical sense. Step-by-Step Solution: Identify the named product: superphosphate typically implies SSP.Recall the reagent: sulphuric acid is used to acidulate rock in SSP.Select “Sulphuric acid” from the list. Verification / Alternative check: Fertilizer process references list SSP as rock phosphate + H2SO4 → monocalcium phosphate + gypsum; TSP is separately produced via phosphoric acid. Why Other Options Are Wrong: Hydrochloric or nitric acid routes are niche and not the standard for superphosphate; phosphoric acid corresponds to TSP, not SSP; acetic acid is irrelevant to industrial phosphate fertilizer production. Common Pitfalls: Confusing the generic term “superphosphate” with “triple superphosphate.” Unless “triple” is specified, the safe exam assumption is SSP with sulphuric acid. Final Answer: Sulphuric acid

Question 17

Electric-furnace phosphorus route and feed quality: Why can low-grade phosphate rock still be used effectively in the electric furnace process?

Accepted Answer

Introduction / Context: The electric-furnace (thermal) process reduces phosphate rock with carbon in the presence of silica to make elemental phosphorus. Unlike wet processes, furnace operation must also manage slags. This question asks why even low-grade phosphate rock can be suitable, focusing on slag chemistry and fluidity, which are critical for furnace tapping and overall process stability. Given Data / Assumptions: Feed: phosphate rock with variable gangue composition, plus coke (carbon) and silica (SiO2). High-temperature electric furnace forms phosphorus vapour and a molten calcium–silicate slag. Goal: maintain a slag composition and viscosity that allow smooth tapping. Concept / Approach: In the furnace, CaO from the rock reacts with SiO2 to form calcium–silicate slags. A favourable CaO/SiO2 ratio yields a low-viscosity, fluid slag that can be tapped and separated from phosphorus vapour. Low-grade ore often carries additional silica-bearing gangue. With proper burden design, this helps achieve a balanced CaO/SiO2 ratio and improves slag fluidity without resorting to excessive flux additions. Thus, “low-grade” does not automatically mean unsuitable; what matters is whether the final CaO–SiO2 balance supports good slag properties. Step-by-Step Solution: Identify furnace needs: fluid slag and sustained phosphorus volatilisation.Relate slag fluidity to CaO/SiO2 ratio in the melt.Note that some low-grade ores contain more silica-bearing gangue.Conclude: a better CaO/SiO2 balance can be achieved, making low-grade rock usable. Verification / Alternative check: Phase diagrams for CaO–SiO2 systems show viscosity minima at certain ratios. Operations target these windows to minimise tapping issues; feeds that naturally hit the ratio require fewer corrections. Why Other Options Are Wrong: Lower CaO content (b): not universally true for all low-grade ores. Cheaper ore (c): economics alone does not guarantee technical suitability. Lower-cost product (d): finished product cost depends on yield/energy, not just ore grade. Impurities raising phosphorus vapour pressure (e): not the controlling mechanism. Common Pitfalls: Equating “low-grade” with “poor performance” without considering flux balance; ignoring that slag chemistry, not just P2O5 grade, controls furnace operability. Final Answer: Because the CaO/SiO2 balance is better for forming a fluid calcium–silicate slag

Question 18

Ostwald step in nitric acid manufacture: Which catalyst is used for the high-temperature oxidation of ammonia to nitric oxide?

Accepted Answer

Introduction / Context: The first step of the Ostwald process oxidizes ammonia (NH3) with air over a precious-metal catalyst to form nitric oxide (NO), which is further processed to nitric acid. Correct identification of the catalyst is fundamental to understanding nitric acid manufacture and the broader nitrogen fertiliser value chain. Given Data / Assumptions: Reaction: NH3 + O2 → NO + H2O (followed by oxidation and absorption). Operating conditions: high temperature, short contact time, gauze catalyst. Catalyst must resist sintering and maintain high selectivity to NO. Concept / Approach: Industrial practice uses woven gauzes of platinum alloyed with rhodium. Rhodium improves mechanical strength, resistance to creep, and selectivity under harsh conditions. Alternative catalysts like vanadium pentoxide are used in different processes (e.g., SO2 oxidation in sulfuric acid manufacture), not in ammonia oxidation. Cobalt–molybdenum sulfide is a hydrotreating catalyst and irrelevant here. Step-by-Step Solution: Map the process: NH3 oxidation step → NO formation on precious-metal gauze.Recall standard alloy: Pt–Rh gauze.Exclude other catalyst families tied to unrelated processes.Select platinum–rhodium gauze as correct. Verification / Alternative check: Plant diagrams and catalyst supplier literature consistently cite Pt–Rh gauze packs for NH3 oxidation, sometimes with palladium catchment for platinum loss control. Why Other Options Are Wrong: Pt–Be or Pt–Mo: non-standard for Ostwald and lack the required proven performance. Co–Mo sulfide: hydrodesulfurization, not NH3 oxidation. V2O5: used for SO2 → SO3, not NH3 → NO. Common Pitfalls: Confusing catalysts between sulfuric and nitric acid industries; overlooking that Ostwald’s step is highly specialised. Final Answer: Platinum–rhodium gauze

Question 19

Urea synthesis conditions: What are the typical temperature and pressure inside the high-pressure urea autoclave where NH3 and CO2 are converted via ammonium carbamate?

Accepted Answer

Introduction / Context: Industrial urea is produced in two main steps: rapid formation of ammonium carbamate from ammonia and carbon dioxide at high pressure, followed by slower dehydration of carbamate to urea and water. This occurs in a high-pressure synthesis section (autoclave/stripper). Recognising the correct operating window is essential for process understanding and troubleshooting. Given Data / Assumptions: Process employs high NH3:CO2 ratio and high pressure to drive carbamate formation. Typical synthesis temperature is in the 170–200 °C range. Typical pressure is in the 140–250 atm range, often near ~200 atm. Concept / Approach: Option (b) best matches common industrial conditions. Too low a temperature slows the dehydration step; too high a temperature may promote side reactions (e.g., biuret) and create materials issues. Very high pressures beyond design norms bring diminishing returns and mechanical penalties, while low pressure cannot maintain the liquid-phase environment needed for efficient carbamate formation and recycle. Step-by-Step Solution: Recall synthesis window: T ≈ 170–200 °C and P ≈ 140–250 atm.Compare with options: 190 °C and 200 atm fits best.Eliminate extremes (e.g., 400 °C/550 atm or 10 atm) as non-representative.Select option (b) as representative of common practice. Verification / Alternative check: Process descriptions and licensor data (e.g., stripping and recycle schemes) publish similar T–P ranges for synthesis loops. Why Other Options Are Wrong: 120 °C/300 atm: temperature too low for practical dehydration kinetics. 400 °C/550 atm: far above standard; materials and side reactions become prohibitive. 200 °C/10 atm: pressure far too low to maintain the required liquid phase. 260 °C/1 atm: non-sensical for synthesis; vacuum is used later in concentration, not in synthesis. Common Pitfalls: Confusing synthesis conditions with downstream evaporation/concentration under vacuum; overemphasising pressure without considering reaction kinetics. Final Answer: 190 °C and 200 atm

Question 20

Definition check: “Nitrolime” refers to which material used in agriculture and industry?

Accepted Answer

Introduction / Context: Nomenclature in fertilisers and agrochemicals can be confusing. The term “nitrolime” has a long history and specifically refers to calcium cyanamide, not nitrate blends. It is valued for multiple roles: as a nitrogenous fertiliser, soil conditioner, and selective weed suppressant in certain crops when properly applied. Given Data / Assumptions: Trade/legacy names may differ regionally, but “nitrolime” is widely equated with CaCN2. Other calcium-containing fertilisers include Ca(NO3)2 and CAN (ammonium nitrate + limestone), which are distinct. Application practices for calcium cyanamide require moisture and time to hydrolyse to plant-available forms. Concept / Approach: Calcium cyanamide is produced by reacting nitrogen with calcium carbide (Frank–Caro process). In soil, it hydrolyses to release plant-available nitrogen and can raise pH locally, also exhibiting herbicidal effects in specific contexts (e.g., onion fields). Therefore, among listed options, only calcium cyanamide correctly matches the definition of “nitrolime.” Step-by-Step Solution: Match the term “nitrolime” with its chemical identity.Exclude calcium nitrate and CAN—both nitrates, not cyanamide.Exclude “nitric acid + lime” and mixed nitrate options, which are not names for CaCN2.Select calcium cyanamide (CaCN2) as the correct definition. Verification / Alternative check: Agronomic references and historical fertiliser literature consistently list “nitrolime” as calcium cyanamide, with guidance on timing and soil conditions for safe, effective use. Why Other Options Are Wrong: Calcium nitrate and CAN are nitrate-based fertilisers; they do not equal nitrolime. “Mixture of nitric acid and lime” and “ammonium nitrate + calcium nitrate” are not standard identities for nitrolime. Common Pitfalls: Assuming any calcium-containing nitrogen fertiliser is “nitrolime”; ignoring the unique cyanamide chemistry. Final Answer: Calcium cyanamide (CaCN2)

Fertiliser Technology Questions