Q: Acidulation of phosphate rock: Reaction of orthophosphoric acid (H3PO4) with phosphate rock primarily produces which commercial fertilizer product?

Introduction / Context: Phosphate fertilizers are made by treating phosphate rock (largely fluorapatite) with acids. The choice of acid determines the product: sulfuric acid produces single superphosphate with gypsum byproduct, whereas phosphoric (orthophosphoric) acid produces a more concentrated, largely water-soluble product known as triple superphosphate (TSP). Given Data / Assumptions: Feed: phosphate rock, chiefly Ca10(PO4)6F2 variants. Acid: orthophosphoric acid (H3PO4), not sulfuric acid. Goal: identify the primary fertilizer produced. Concept / Approach: Acidulation with H3PO4 converts the insoluble rock phosphates into monocalcium phosphate, Ca(H2PO4)2, with minimal gypsum formation. This results in triple superphosphate, a high-analysis P fertilizer (typically about 44–46% P2O5) with good water solubility, suitable for various crops and soils when properly placed. Step-by-Step Solution: Recognize acid choice: H2SO4 → SSP; H3PO4 → TSP.Identify main chemical form in TSP: Ca(H2PO4)2 (monocalcium phosphate).Select TSP as the product of rock + H3PO4. Verification / Alternative check: Process descriptions of TSP plants show digestion of rock with merchant-grade phosphoric acid, granulation, and drying to yield high P2O5 product. Why Other Options Are Wrong: SSP results from sulfuric acid treatment and contains gypsum. Metaphosphoric acid is a condensed phosphate not directly produced by this route. MAP and DAP require neutralization of phosphoric acid with ammonia, not rock acidulation alone. Common Pitfalls: Conflating “superphosphate” generically with SSP; the type of acid matters for the final product composition and analysis. Final Answer: Triple superphosphate (TSP).

Q: Phosphatic fertilizer analysis: A fertilizer labeled 16% P2O5 would most likely be which product grade?

Introduction / Context: Fertilizer grades for phosphate are often expressed as percent P2O5. Recognizing typical analysis values helps identify the product. Single superphosphate (SSP) has substantially lower P2O5 content than triple superphosphate (TSP) or ammonium phosphates (MAP/DAP), making it the best match to a 16% P2O5 label among common products. Given Data / Assumptions: Target analysis ≈ 16% P2O5. Product candidates include SSP, TSP, DCP, and ammonium phosphates. Standard commercial specifications are assumed. Concept / Approach: Typical P2O5 analyses: SSP about 16–20% (often near 16–18% depending on process and moisture), TSP about 44–46%, DAP about 46% P2O5 with high N content, and DCP products are substantially higher than 16% and used more in feed/phosphate blends. Therefore, the fertilizer closest to 16% P2O5 is SSP. Step-by-Step Solution: Recall standard grades: SSP ≈ 16–20% P2O5; TSP ≈ 44–46%; DAP ≈ 46%.Match the given 16% value to SSP.Select SSP as the correct answer. Verification / Alternative check: Product datasheets and national fertilizer standards list SSP around 16% available P2O5, confirming the match. Why Other Options Are Wrong: TSP/DAP: far higher P2O5 content than 16%. DCP: not typically marketed as a 16% P2O5 fertilizer; higher analysis. None of these: incorrect since SSP fits. Common Pitfalls: Confusing P2O5 percent with elemental phosphorus percent; P2O5 values are higher numerically than elemental P for the same product. Final Answer: Single superphosphate (superphosphate, SSP).

Q: Identify the compound: The chemical formula CaH4(PO4)2 corresponds most directly to which fertilizer compound in common nomenclature?

Introduction / Context: Superphosphates are described by their dominant phosphate species. The formula CaH4(PO4)2 is another way of writing Ca(H2PO4)2, the monocalcium phosphate that constitutes the active, water-soluble component of triple superphosphate (TSP). Recognizing this mapping is useful when cross-referencing fertilizer labels and chemical formulations. Given Data / Assumptions: CaH4(PO4)2 ≡ Ca(H2PO4)2 (monocalcium phosphate). TSP is produced by reacting phosphate rock with phosphoric acid to yield monocalcium phosphate. SSP contains monocalcium phosphate plus significant gypsum; TSP is the concentrated form. Concept / Approach: Because TSP is largely monocalcium phosphate with minimal gypsum, the neat formula Ca(H2PO4)2 is commonly associated with TSP in textbook representations. SSP, while containing the same monocalcium species, also contains 2 CaSO4 equivalents (gypsum), so it is not represented simply by Ca(H2PO4)2. Tricalcium phosphate corresponds to rock phosphate; metaphosphoric acid is a condensed phosphate, not a calcium salt. Step-by-Step Solution: Translate the formula: CaH4(PO4)2 = Ca(H2PO4)2.Associate monocalcium phosphate with TSP as the concentrated product.Select triple superphosphate as the best match. Verification / Alternative check: Manufacturing routes and product specifications list TSP as primarily monocalcium phosphate, while SSP is Ca(H2PO4)2 + CaSO4. Why Other Options Are Wrong: SSP: includes substantial gypsum; not represented by the pure monocalcium formula. Tricalcium phosphate: Ca3(PO4)2, not Ca(H2PO4)2. Metaphosphoric acid: polymeric phosphates without calcium. Dicalcium phosphate: CaHPO4, different stoichiometry. Common Pitfalls: Assuming SSP and TSP are chemically identical; they differ in concentration and associated salts, even though both contain monocalcium phosphate. Final Answer: Triple superphosphate (monocalcium phosphate rich).

Q: In industrial fertiliser manufacture, the reaction between liquid ammonia (NH3) and 60% nitric acid (HNO3) to produce ammonium nitrate (NH4NO3) is thermally characterized as which type of reaction?

Introduction / Context: The neutralisation of nitric acid with anhydrous or aqueous ammonia to form ammonium nitrate is a key step in nitrogen fertiliser production. Correctly identifying the reaction heat effect is essential for safe reactor design, heat removal, and preventing runaway conditions in neutralisers and prilling/granulation units. Given Data / Assumptions: Reactants: liquid NH3 and ~60% HNO3. Product: ammonium nitrate solution, NH4NO3(aq). Operation commonly carried out in well-cooled neutralisers. Concept / Approach: Acid–base neutralisation reactions typically release heat. The formation of ammonium nitrate from ammonia and nitric acid is strongly exothermic, demanding vigorous heat removal to control temperature and avoid excessive vapour generation and decomposition risks downstream. Step-by-Step Solution: Recognise acid–base neutralisation: NH3 + HNO3 → NH4NO3.Recall that neutralisation enthalpies are negative (heat released).Industrial practice uses cooling coils/evaporative cooling in neutralisers, confirming significant heat evolution.Therefore, classify the reaction as exothermic. Verification / Alternative check: Plant heat balances show that substantial cooling duty is required during neutralisation, and neutraliser temperatures are tightly controlled to protect product quality and safety. Why Other Options Are Wrong: Endothermic: contradicts observed heat release. Autocatalytic: the reaction does not require self-catalysis; it is a straightforward neutralisation. None of these or reversible only at very high pressure: irrelevant to this neutralisation step. Common Pitfalls: Confusing the safe neutralisation step with the thermal stability of concentrated ammonium nitrate; decomposition hazards are separate from the neutralisation exotherm. Final Answer: exothermic

Q: In phosphorus processing, the conversion of yellow (white) phosphorus to red phosphorus is carried out at 250–450 °C. Under which atmosphere/condition is this transformation correctly performed in industrial retorts?

Introduction / Context: Yellow (white) phosphorus is thermodynamically less stable and more reactive than red phosphorus. Converting it to the safer, polymeric red allotrope is an important conditioning step for matches, pyrotechnics, and certain fertiliser intermediates. The operating environment (presence or absence of oxygen) critically affects both yield and safety. Given Data / Assumptions: Temperature range: 250–450 °C in retorts. Objective: allotrope conversion without oxidation/combustion. Industrial practice employs sealed vessels and inert purges. Concept / Approach: Yellow phosphorus readily oxidises in air and can ignite. The conversion to red phosphorus must therefore be performed without oxygen present—operationally described as “in the absence of air,” often implemented by an inert purge (e.g., nitrogen) to displace oxygen and moisture. Step-by-Step Solution: Identify hazard: yellow phosphorus oxidises/ignites in air.Choose safe converting environment: no oxygen present.Industrial translation: sealed retorts under inert purge or vacuum → effectively absence of air.Hence, the correct condition is the absence of air. Verification / Alternative check: Process descriptions specify inert atmospheres to prevent oxidation; this is operationally equivalent to maintaining an oxygen-free space. Why Other Options Are Wrong: Oxidising atmosphere: would oxidise/ignite phosphorus. Reducing atmosphere: unnecessary and may introduce side reactions. Steam-rich: risks hydrolysis/oxidation issues. Inert atmosphere: often used, but the core requirement tested by many MCQs is “absence of air”. Common Pitfalls: Equating “inert” strictly with nitrogen presence; the principle is preventing oxygen access, i.e., air-free conditions. Final Answer: absence of air

Q: Phosphate rock used in fertiliser manufacture predominantly consists of which mineral species?

Introduction / Context: Natural phosphate rock is the primary source of phosphorus for fertiliser production. Knowing its dominant mineralogy is important for selecting acidulation conditions, impurity management, and environmental controls for fluoride emissions. Given Data / Assumptions: Feed is geological “phosphate rock.” Processing routes include wet-process phosphoric acid and direct acidulation to superphosphates. Concept / Approach: Most commercial phosphate rock is a form of apatite, commonly fluorapatite (also called fluoroapatite), with idealised composition Ca5(PO4)3F or equivalently 3Ca3(PO4)2·CaF2. The fluoride in the lattice explains HF/SiF4 evolution during acidulation and the need for fluorine scrubbing. Step-by-Step Solution: Identify apatite family as dominant P-bearing minerals.Select the fluoride-bearing member: fluorapatite, Ca5(PO4)3F.Dismiss non-fertility compounds: ammonium phosphate is manufactured, not a rock mineral.Therefore, the main constituent is fluorapatite. Verification / Alternative check: Analyses of sedimentary and igneous phosphate ores consistently report fluorapatite as the principal phase, with variable substitution and impurity content. Why Other Options Are Wrong: Ammonium phosphate: synthetic fertiliser, not a rock mineral. Calcium fluoride: occurs as fluorite, not the main P carrier. Calcium phosphate (unspecified): too vague; apatite structure is the correct identification. Hydroxyapatite only: present in some ores but fluorapatite predominates. Common Pitfalls: Equating generic “calcium phosphate” with the specific apatite minerals; process design hinges on the fluoride-bearing nature of fluorapatite. Final Answer: fluorapatite (Ca5(PO4)3F)

Question 1

Fertiliser classification: Which of the following is not considered a mixed fertiliser (i.e., does not supply more than one primary plant nutrient among N, P, K)?

Accepted Answer

Introduction / Context: Mixed fertilisers supply more than one primary nutrient among nitrogen (N), phosphorus (P), and potassium (K). This classification guides farmers in meeting balanced nutrient requirements. The question asks you to spot the product that does not qualify as mixed by this definition. Given Data / Assumptions: Primary nutrients are N, P, K. Secondary nutrients (e.g., Ca, S, Mg) do not by themselves make a fertiliser “mixed”. We use conventional industry definitions. Concept / Approach: Nitrophosphate contains N and P; ammonium phosphate contains N and P; UAN contains N in two forms but no P or K. Calcium ammonium nitrate provides nitrogen with calcium as a conditioner/secondary nutrient. By the strict “primary nutrients” definition, CAN supplies only one primary nutrient (N), thus it is not a mixed fertiliser, whereas nitrophosphates and ammonium phosphates are mixed (N + P). UAN also supplies only N; however, among the original choices commonly debated, CAN is the classic answer in many exam keys. Here we include UAN as a distractor to test understanding of “primary” versus “secondary”. Step-by-Step Solution: List primary nutrients each option supplies.Nitrophosphate → N + P (mixed).Ammonium phosphate → N + P (mixed).CAN → N + Ca (Ca is secondary) → only one primary.Therefore, CAN is not a mixed fertiliser by the NPK definition. Verification / Alternative check: Fertiliser labeling standards treat CAN as a straight nitrogen fertiliser with added calcium carbonate; nitrophosphates and ammonium phosphates are explicitly NP grades. Why Other Options Are Wrong: Nitrophosphate: supplies N and P → mixed. Ammonium phosphate: supplies N and P → mixed. None of these: incorrect because CAN is not mixed. Urea–ammonium nitrate: provides only N, but CAN is the typical textbook answer; UAN is presented here as a distractor emphasizing “primary” nutrients. Common Pitfalls: Counting calcium as a primary nutrient; conflating “two nitrogen forms” with “two primary nutrients”. Final Answer: Calcium ammonium nitrate (CAN)

Question 2

CAN manufacture basics: Which combination of raw materials is required, along with NH3, to produce calcium ammonium nitrate (CAN)?

Accepted Answer

Introduction / Context: Calcium ammonium nitrate (CAN) is a granular straight nitrogen fertiliser stabilized with calcium carbonate or limestone to reduce caking and acidity. Understanding the required raw materials clarifies process flows in integrated nitric acid–ammonium nitrate complexes. Given Data / Assumptions: Ammonium nitrate is made from NH3 + HNO3. CAN incorporates limestone or dolomite as a conditioner. We seek the materials used jointly with NH3. Concept / Approach: First, ammonia and nitric acid react exothermically to form ammonium nitrate solution. This solution is then neutralized/conditioned and granulated with finely ground limestone (or dolomite) to produce CAN prills or granules with improved physical properties and less acidifying effect in soil. CO2, H2SO4, KNO3, or NH4Cl are not required for this standard route. Step-by-Step Solution: Generate AN: NH3 + HNO3 → NH4NO3 (solution).Blend with limestone/dolomite: provides CaCO3 matrix.Granulate/dry to obtain CAN product.Therefore, the required inputs (besides NH3) are HNO3 and limestone. Verification / Alternative check: Process block diagrams of CAN plants consistently show nitric acid and limestone additions upstream of granulation. Why Other Options Are Wrong: CO2 and H2SO4: unrelated to CAN synthesis. HNO3 and NH4Cl: NH4Cl is not part of CAN; it is itself a nitrogen fertiliser. CO2 and KNO3: KNO3 is a different fertiliser (potassium nitrate). NH3 only: cannot produce CAN without nitric acid and limestone. Common Pitfalls: Confusing CAN with calcium nitrate or ammonium sulphate; assuming CO2 neutralization is used instead of limestone conditioning. Final Answer: HNO3 and limestone

Question 3

Steam reforming of naphtha: What is the typical optimum reaction temperature range (°C) used in primary reformers?

Accepted Answer

Introduction / Context: Steam reforming converts hydrocarbons (e.g., naphtha) into synthesis gas (H2, CO, CO2). The endothermic reforming reactions require high temperature to achieve practical equilibrium conversion and catalyst activity. This question asks for the customary temperature range employed in industrial primary reformers processing naphtha. Given Data / Assumptions: Feed: light hydrocarbon/naphtha with steam. Catalyst: Ni-based reforming catalyst. Tubular fired furnace providing heat to reach outlet temperatures in the upper range. Concept / Approach: Industrial practice targets outlet temperatures roughly 780–900 °C, with furnace bridgewall temperatures higher to drive heat into tubes. The broader standard range cited in textbooks for reforming operation envelopes is approximately 700–1000 °C, encompassing inlet-to-outlet conditions and different feed severities. Lower ranges (300–450 °C) suit shift or methanation; extremely high ranges (1500–1700 °C) are for processes like partial oxidation flames, not catalytic reforming. Step-by-Step Solution: Identify reaction type: highly endothermic steam reforming.Match with Ni-catalyst activity window: high-temperature regime.Select the range that includes typical outlet temperatures.Therefore, 700–1000 °C is the correct range. Verification / Alternative check: Design manuals and licensor data show reformer outlet temperatures near 800–900 °C for naphtha feeds, confirming the chosen range. Why Other Options Are Wrong: 300–450 °C, 100–200 °C, 450–550 °C: far too low for reforming; these correspond to other unit operations. 1500–1700 °C: flame temperatures of partial oxidation, not tubular catalytic reforming. Common Pitfalls: Confusing reforming with secondary reforming or POX; mixing up bed outlet temperature with furnace wall temperature. Final Answer: 700 – 1000 °C

Question 4

Statements on nitrogen fertiliser processes: Which of the following is correct regarding urea/AN manufacture and by-products?

Accepted Answer

Introduction / Context: Industrial nitrogen fertilisers include ammonium nitrate (AN) and urea. Safety, equilibrium, and quality aspects are central to plant design and agronomy. This question checks knowledge of reaction energetics, synthesis stoichiometry, and the agronomic impact of impurities such as biuret formed by urea condensation at high temperatures. Given Data / Assumptions: AN forms from ammonia and nitric acid in a neutralization reactor. Urea forms from ammonia and carbon dioxide via ammonium carbamate. Biuret forms when urea condenses at elevated temperature during finishing. Concept / Approach: The AN neutralization is strongly exothermic, providing heat for concentration. In urea synthesis, increasing the NH3/CO2 ratio generally aids conversion to urea (ammonia excess), not decreases it. Biuret is phytotoxic above certain levels; fertiliser-grade urea is specified with low biuret content to avoid seedling damage and animal health issues when misused. Step-by-Step Solution: Evaluate (a): AN formation is exothermic → statement (a) is false.Evaluate (b): Higher NH3/CO2 typically increases, not decreases, urea yield → statement (b) is false.Evaluate (c): Biuret toxicity is documented → statement (c) is true.Therefore, the only correct statement is (c). Verification / Alternative check: Plant design texts list AN neutralizer heat duties as net exothermic; urea synthesis models show improved conversion with ammonia excess; agronomy guides caution against high-biuret urea for sensitive crops. Why Other Options Are Wrong: (a) Endothermic claim contradicts neutralization thermochemistry. (b) Decrease in yield with higher NH3/CO2 contradicts equilibrium trends. (d) Includes (b), which is false. (e) Includes multiple false assertions. Common Pitfalls: Assuming all neutralizations are mild; AN is notably exothermic. Confusing optimal NH3/CO2 with infinite excess—excess helps conversion but is balanced against corrosion and stripping duties. Final Answer: Biuret, an intermediate/by-product during urea manufacture, is toxic to seeds and animals

Question 5

Indian rock phosphate mining: At which location is the country’s major rock phosphate deposit classically mined and cited in fertiliser engineering texts?

Accepted Answer

Introduction / Context: Rock phosphate is the principal raw material for phosphatic fertilisers. Knowing the major mining locations helps link raw material logistics to plant siting and process economics in India. This question asks for the canonical site widely referenced for domestic rock phosphate mining. Given Data / Assumptions: We focus on well-established, large deposits. The distractors list well-known mining regions for other minerals. Accuracy takes precedence over legacy state names. Concept / Approach: India’s most cited rock phosphate deposit is the Jhamarkotra mine near Udaipur in Rajasthan, operated by state enterprises. Other locations in the options are associated with coal (Talcher) or iron ore (Bailadila, Kiriburu), or with pyrite (Amjhore), and are not primary rock phosphate sources for fertiliser manufacture. Step-by-Step Solution: Identify which option corresponds to a major phosphate deposit.Recognize Jhamarkotra (Rajasthan) as the correct phosphate site.Eliminate locations tied to other minerals (coal, iron ore, pyrite).Select Jhamarkotra, Rajasthan. Verification / Alternative check: Geological and fertiliser-industry references consistently list Jhamarkotra as India’s largest rock phosphate mine, supplying SSP/TSP and wet-process phosphoric acid plants. Why Other Options Are Wrong: Talcher: coal mining; not rock phosphate. Bailadila: iron ore deposits. Kiriburu: iron ore region. Amjhore: pyrite used historically for sulphuric acid, not rock phosphate. Common Pitfalls: Confusing pyrite and phosphate raw materials because both link to sulphuric acid use; mixing ore names with deposit locations. Final Answer: Jhamarkotra, Rajasthan (Udaipur district)

Question 6

Identify the fertiliser grade: A nitrogenous fertiliser contains about 20% nitrogen by mass. Which product best matches this analysis?

Accepted Answer

Introduction / Context: Fertiliser labeling specifies the mass percentage of nutrients, especially nitrogen in nitrogenous products. Being able to match an assay (e.g., ~20% N) to a likely product is a basic competency in agronomy and process operations. This item asks which common fertiliser aligns with an N analysis close to 20%. Given Data / Assumptions: Target nitrogen content ≈ 20% by mass. We compare against typical specification values for standard fertilisers. Minor regional formulation variations are ignored; use nominal textbook values. Concept / Approach: Typical nitrogen contents are: urea ≈ 46% N, ammonium nitrate ≈ 33–35% N, ammonium chloride ≈ 25–26% N, calcium ammonium nitrate (solid) ≈ 26–28% N, and ammonium sulphate ≈ 21% N. Of these, ammonium sulphate most closely matches the stated ~20% N content. Therefore it is the best match among the options provided. Step-by-Step Solution: List nominal N% for each candidate.Compare against the target 20%.Identify the closest: ammonium sulphate ≈ 21% N.Select ammonium sulphate as the correct choice. Verification / Alternative check: Product datasheets and fertiliser handbooks report ammonium sulphate grades around 20–21% N, confirming the match. Why Other Options Are Wrong: Ammonium nitrate: typically ~33–35% N. Calcium ammonium nitrate: usually ~26–28% N (solid grade). Urea: ~46% N, far above 20%. Ammonium chloride: ~25–26% N, not ~20%. Common Pitfalls: Assuming CAN could be formulated as low as 20% N (standard solid grades are higher); confusing mass percentages with nutrient oxide equivalents used in NPK labels for P and K. Final Answer: Ammonium sulphate

Question 7

Ostwald process for nitric acid (HNO3): In the platinum-catalyzed synthesis where conversion to NO is 95–97%, the subsequent gas-phase formation of nitrogen dioxide (2 NO + O2 → 2 NO2) is favored, from an equilibrium standpoint, by what change in co…

Accepted Answer

Introduction / Context: The Ostwald process produces nitric acid (HNO3) via catalytic oxidation of ammonia over platinum gauze to nitric oxide (NO), followed by homogeneous gas-phase oxidation of NO to nitrogen dioxide (NO2) and subsequent absorption to form HNO3. After the first high-temperature catalytic step, plant designers tune temperature and pressure in the downstream gas path to maximize NO → NO2 conversion before absorption. This question focuses specifically on the oxidation equilibrium of NO to NO2. Given Data / Assumptions: Main reaction considered: 2 NO(g) + O2(g) → 2 NO2(g). The first-stage ammonia conversion over Pt is high (about 95–97%). We are asking which change favors NO2 formation in the second step. Ideal gas behavior and standard thermochemical tendencies are assumed. Concept / Approach: The oxidation of NO to NO2 is exothermic and goes from 3 mol of gas on the left to 2 mol on the right. By Le Châtelier’s principle: lowering temperature favors an exothermic forward reaction, and increasing pressure favors the side with fewer moles. Thus, at fixed pressure, decreasing temperature increases the equilibrium fraction of NO2. Practically, plants cool the gas after the hot Pt gauze to promote NO oxidation before absorption towers. Although reaction rates slow as temperature decreases, in typical ranges the equilibrium benefit dominates and residence time/oxidant excess are adjusted accordingly. Step-by-Step Solution: Identify reaction: 2 NO + O2 → 2 NO2 (exothermic, ΔH < 0).Apply Le Châtelier to temperature: lower T shifts equilibrium toward NO2.Apply Le Châtelier to pressure: higher P would also favor NO2, but that option is not presented.Therefore, among the given choices, decreasing temperature is the change that favors NO2 formation. Verification / Alternative check: Plant practice includes gas cooling between stages and before absorption; cooler gas streams show higher NO2/NO ratios at equilibrium, improving nitric acid yields upon absorption. Why Other Options Are Wrong: Decreasing pressure: would favor the side with more moles (reactants), opposing NO2 formation. Increasing temperature: shifts an exothermic equilibrium backwards toward NO. None of these: incorrect because decreasing temperature does favor NO2. Increasing moisture content: moisture affects absorption, not the gas-phase oxidation equilibrium directly. Common Pitfalls: Confusing equilibrium preference with reaction rate. While higher temperature can speed kinetics, the question asks what favors formation (equilibrium). Process control balances both by cooling and ensuring adequate residence time and oxygen availability. Final Answer: Decreasing the temperature.

Question 8

Urea manufacturing chemistry: The formation of ammonium carbamate from ammonia and carbon dioxide (2 NH3 + CO2 → NH2COONH4) is best described as which type of process step?

Accepted Answer

Introduction / Context: Modern urea plants operate by first forming ammonium carbamate from ammonia and carbon dioxide at high pressure and moderate temperature, followed by endothermic dehydration of carbamate to urea. Recognizing the thermodynamic character of the carbamate-forming step is essential for understanding the recycle loops, heat integration, and the need for high-pressure operation in urea technology. Given Data / Assumptions: Reaction considered: 2 NH3 + CO2 → NH2COONH4 (ammonium carbamate). Typical operating window: high pressure (often 130–180 bar) and moderate temperature. No solid catalyst is employed in this step. Concept / Approach: Ammonium carbamate formation releases heat (it is exothermic) and reaches equilibrium rapidly under pressure. Because it is reversible and equilibrium-limited, plant designs use elevated pressure to shift equilibrium toward carbamate, enabling high overall conversion in the synthesis loop. No catalyst is required; instead, thermodynamic driving forces (pressure and temperature) govern conversion, while subsequent decomposition/stripping and recycling recover unconverted reactants. Step-by-Step Solution: Write the step: 2 NH3 + CO2 → NH2COONH4.Classify energetics: heat is released → exothermic.Classify reversibility: carbamate can dissociate back to NH3 + CO2 → reversible.Identify catalysis: no heterogeneous catalyst used → non-catalytic.Therefore, the correct characterization is non-catalytic, exothermic, and reversible. Verification / Alternative check: Process flow descriptions and energy balances show heat recovery from the synthesis section due to exothermic carbamate formation and the need for strippers/condensers because of reversibility. Why Other Options Are Wrong: Catalytic/endothermic/irreversible: contradicts standard plant chemistry. Photochemical/free-radical: unrelated to high-pressure carbamate formation. Electrochemical: not part of thermal urea synthesis. Purely physical absorption: chemical bonding occurs; it is not just dissolution. Common Pitfalls: Mixing this step with the subsequent dehydration (which is endothermic) or assuming catalyst usage because many industrial reactions are catalytic. Urea synthesis relies more on pressure-driven equilibrium than on solid catalysts. Final Answer: Non-catalytic, exothermic, and reversible (equilibrium-limited).

Question 9

Fertilizer sources: Which of the following is a natural inorganic (mineral) fertilizer material as obtained from nature and historically used directly?

Accepted Answer

Introduction / Context: Fertilizer materials can be categorized as organic (derived from plant/animal matter) or inorganic/mineral (derived from geologic deposits or chemical processing). Understanding classic examples helps in recognizing nutrient analysis, solubility, and application behavior. Chile saltpetre is an iconic natural mineral source of nitrate nitrogen historically mined in Chile’s Atacama desert. Given Data / Assumptions: “Natural inorganic” means mineral sources occurring in nature with minimal processing. Organic manures like oilcakes and farmyard manure are biologically derived and carbon-rich. We are comparing common textbook examples. Concept / Approach: Chile saltpetre is sodium nitrate (NaNO3), a natural mineral deposit used as a direct-application nitrogen fertilizer. By contrast, oilcakes (mustard, groundnut) and gobar manure are organic fertilizers releasing nutrients via mineralization. Bone meal, while mineral-rich in calcium phosphates, is of animal origin and generally classed as organic/mineral-organic rather than “natural inorganic” in the classical agronomy sense used in such MCQs. Step-by-Step Solution: Define the category: naturally occurring, inorganic mineral.List candidates: sodium nitrate deposits from Chile qualify.Reject organics: oilcake and farmyard manure are organic.Therefore select Chile saltpetre as the correct mineral fertilizer. Verification / Alternative check: Historic fertilizer trade records and agronomy texts list sodium nitrate as a natural mineral nitrogen source used before widespread synthetic ammonia production. Why Other Options Are Wrong: Oilcake and gobar manure are organic fertilizers, not inorganic minerals. Bone meal is animal-derived and not typically categorized as a pure mineral fertilizer. “None of these” is incorrect because Chile saltpetre fits the definition. Common Pitfalls: Equating “contains minerals” with “mineral fertilizer.” The classification depends on origin and processing, not just chemical species present. Final Answer: Chile saltpetre (sodium nitrate).

Question 10

Acidulation of phosphate rock: Reaction of orthophosphoric acid (H3PO4) with phosphate rock primarily produces which commercial fertilizer product?

Accepted Answer

Introduction / Context: Phosphate fertilizers are made by treating phosphate rock (largely fluorapatite) with acids. The choice of acid determines the product: sulfuric acid produces single superphosphate with gypsum byproduct, whereas phosphoric (orthophosphoric) acid produces a more concentrated, largely water-soluble product known as triple superphosphate (TSP). Given Data / Assumptions: Feed: phosphate rock, chiefly Ca10(PO4)6F2 variants. Acid: orthophosphoric acid (H3PO4), not sulfuric acid. Goal: identify the primary fertilizer produced. Concept / Approach: Acidulation with H3PO4 converts the insoluble rock phosphates into monocalcium phosphate, Ca(H2PO4)2, with minimal gypsum formation. This results in triple superphosphate, a high-analysis P fertilizer (typically about 44–46% P2O5) with good water solubility, suitable for various crops and soils when properly placed. Step-by-Step Solution: Recognize acid choice: H2SO4 → SSP; H3PO4 → TSP.Identify main chemical form in TSP: Ca(H2PO4)2 (monocalcium phosphate).Select TSP as the product of rock + H3PO4. Verification / Alternative check: Process descriptions of TSP plants show digestion of rock with merchant-grade phosphoric acid, granulation, and drying to yield high P2O5 product. Why Other Options Are Wrong: SSP results from sulfuric acid treatment and contains gypsum. Metaphosphoric acid is a condensed phosphate not directly produced by this route. MAP and DAP require neutralization of phosphoric acid with ammonia, not rock acidulation alone. Common Pitfalls: Conflating “superphosphate” generically with SSP; the type of acid matters for the final product composition and analysis. Final Answer: Triple superphosphate (TSP).

Question 11

Soil reaction for crops: For general field crops, the target soil pH maintained by fertilization and liming practices for optimum growth is typically in which range?

Accepted Answer

Introduction / Context: Soil pH strongly affects nutrient availability, microbial activity, and root health. Most agronomic recommendations aim for near-neutral conditions for broad-acre crops, adjusting with lime or acidifying amendments as needed. This question asks you to identify a typical target interval for general crop production, recognizing that some specialty crops have different preferences. Given Data / Assumptions: General mixed farming context (cereals, legumes, oilseeds). Balanced fertilizer use and standard soil amendments. No highly specialized crops like blueberries (acid-loving) or asparagus (alkaline-tolerant) are implied. Concept / Approach: Availability of major nutrients (N, P, K) and many micronutrients is maximized near neutral pH. While the absolute optimum for many crops can lie between pH 6.0 and 7.5, many extension guides accept a practical operating window extending to about pH 7–8, particularly in calcareous regions where complete neutralization is impractical. Thus, among the given ranges, 7–8 best represents the typical management target opposed to clearly suboptimal extremes. Step-by-Step Solution: Recall nutrient availability curves peak near neutral pH.Recognize agronomic practice: liming acidic soils toward neutrality; avoiding strong alkalinity.From the given options, select pH 7–8 as the best general-purpose target. Verification / Alternative check: Soil-testing recommendations often prescribe lime to raise pH into the 6.5–7.0+ zone; in calcareous soils, management within 7–8 is common and productive. Why Other Options Are Wrong: pH 4–5: severely acidic; aluminum toxicity and P fixation limit growth. pH 9–10 or 12–13: highly alkaline/caustic; micronutrient deficiencies and structure issues. pH 2–3: extremely acidic and unsuitable for crops. Common Pitfalls: Assuming one universal ideal pH; crop-specific and soil-specific targets exist, but general field practice avoids strong acidity or alkalinity. Final Answer: pH 7–8 (near neutral to mildly alkaline).

Question 12

Elemental phosphorus recovery: Approximate overall yield of elemental phosphorus obtained from rock phosphate by thermal reduction in an electric furnace is typically in which range?

Accepted Answer

Introduction / Context: Elemental phosphorus (usually white or yellow P4) is produced industrially by carbothermal reduction of phosphate rock with silica and coke in an electric furnace. Understanding typical material yields helps in evaluating process economics, energy use, and byproduct handling (silicate slags, fluorine compounds). This question asks for the approximate overall yield range realized in practice from rock phosphate feed. Given Data / Assumptions: Feed: beneficiated phosphate rock with typical P2O5 content. Process: high-temperature electric furnace reduction with coke and silica. Yield refers to elemental phosphorus recovery relative to phosphorus content of feed. Concept / Approach: In the thermal route, not all phosphorus in the rock is recovered as P4 due to incomplete reduction, volatilization losses, and retention in slag phases. Operational data commonly place overall recoveries in the mid ranges rather than near 100%. Among the presented options, a 60–65% yield window is representative of practical, large-scale furnace operation when considering feed variability and process constraints. Step-by-Step Solution: Identify process chemistry: reduction of Ca-phosphates to P4, CO, and Ca-silicates.Consider losses: slag retention and volatilized species reduce recovery.Select a mid-range, realistic yield from the options: 60–65%. Verification / Alternative check: Industry summaries and textbook examples cite recoveries well below 100% for the electric furnace process, with improvements possible through feed preparation and furnace control but typically not approaching the 90–95% figure in routine operation. Why Other Options Are Wrong: 1–2% and 15–25%: far too low for an established industrial process. 40–45%: underrepresents feasible recoveries. 90–95%: overly optimistic given real plant losses. Common Pitfalls: Confusing elemental phosphorus yield with fertilizer-grade phosphoric acid yields from “wet process,” which follow different chemistry and recovery metrics. Final Answer: 60–65%.

Question 13

Phosphatic fertilizer analysis: A fertilizer labeled 16% P2O5 would most likely be which product grade?

Accepted Answer

Introduction / Context: Fertilizer grades for phosphate are often expressed as percent P2O5. Recognizing typical analysis values helps identify the product. Single superphosphate (SSP) has substantially lower P2O5 content than triple superphosphate (TSP) or ammonium phosphates (MAP/DAP), making it the best match to a 16% P2O5 label among common products. Given Data / Assumptions: Target analysis ≈ 16% P2O5. Product candidates include SSP, TSP, DCP, and ammonium phosphates. Standard commercial specifications are assumed. Concept / Approach: Typical P2O5 analyses: SSP about 16–20% (often near 16–18% depending on process and moisture), TSP about 44–46%, DAP about 46% P2O5 with high N content, and DCP products are substantially higher than 16% and used more in feed/phosphate blends. Therefore, the fertilizer closest to 16% P2O5 is SSP. Step-by-Step Solution: Recall standard grades: SSP ≈ 16–20% P2O5; TSP ≈ 44–46%; DAP ≈ 46%.Match the given 16% value to SSP.Select SSP as the correct answer. Verification / Alternative check: Product datasheets and national fertilizer standards list SSP around 16% available P2O5, confirming the match. Why Other Options Are Wrong: TSP/DAP: far higher P2O5 content than 16%. DCP: not typically marketed as a 16% P2O5 fertilizer; higher analysis. None of these: incorrect since SSP fits. Common Pitfalls: Confusing P2O5 percent with elemental phosphorus percent; P2O5 values are higher numerically than elemental P for the same product. Final Answer: Single superphosphate (superphosphate, SSP).

Question 14

Identify the compound: The chemical formula CaH4(PO4)2 corresponds most directly to which fertilizer compound in common nomenclature?

Accepted Answer

Introduction / Context: Superphosphates are described by their dominant phosphate species. The formula CaH4(PO4)2 is another way of writing Ca(H2PO4)2, the monocalcium phosphate that constitutes the active, water-soluble component of triple superphosphate (TSP). Recognizing this mapping is useful when cross-referencing fertilizer labels and chemical formulations. Given Data / Assumptions: CaH4(PO4)2 ≡ Ca(H2PO4)2 (monocalcium phosphate). TSP is produced by reacting phosphate rock with phosphoric acid to yield monocalcium phosphate. SSP contains monocalcium phosphate plus significant gypsum; TSP is the concentrated form. Concept / Approach: Because TSP is largely monocalcium phosphate with minimal gypsum, the neat formula Ca(H2PO4)2 is commonly associated with TSP in textbook representations. SSP, while containing the same monocalcium species, also contains 2 CaSO4 equivalents (gypsum), so it is not represented simply by Ca(H2PO4)2. Tricalcium phosphate corresponds to rock phosphate; metaphosphoric acid is a condensed phosphate, not a calcium salt. Step-by-Step Solution: Translate the formula: CaH4(PO4)2 = Ca(H2PO4)2.Associate monocalcium phosphate with TSP as the concentrated product.Select triple superphosphate as the best match. Verification / Alternative check: Manufacturing routes and product specifications list TSP as primarily monocalcium phosphate, while SSP is Ca(H2PO4)2 + CaSO4. Why Other Options Are Wrong: SSP: includes substantial gypsum; not represented by the pure monocalcium formula. Tricalcium phosphate: Ca3(PO4)2, not Ca(H2PO4)2. Metaphosphoric acid: polymeric phosphates without calcium. Dicalcium phosphate: CaHPO4, different stoichiometry. Common Pitfalls: Assuming SSP and TSP are chemically identical; they differ in concentration and associated salts, even though both contain monocalcium phosphate. Final Answer: Triple superphosphate (monocalcium phosphate rich).

Question 15

Hydrogen supply for ammonia manufacture (Indian context): Which route is generally the costliest per unit hydrogen among the options listed?

Accepted Answer

Introduction / Context: Large-scale ammonia manufacture requires a reliable and economical hydrogen source. In India, as elsewhere, hydrogen production economics depend on feedstock and energy prices. This item asks you to identify the generally costliest option among common industrial choices when evaluated on a levelized cost basis absent special subsidies for electricity. Given Data / Assumptions: Conventional plant scales; grid or typical industrial power tariffs. Standard process configurations as used in fertilizer sectors. No extraordinary low-cost renewable power assumed for electrolysis. Concept / Approach: Steam reforming of natural gas (or naphtha where applicable) has historically delivered the lowest-cost hydrogen at scale. By-product recovery from coke oven gas can be attractive in integrated steel complexes. Electrolysis of water, while attractive for decarbonization, consumes large amounts of electricity; without very cheap power, its cost per kilogram H2 is higher than reforming-based routes, making it the costliest among the options under typical Indian industrial conditions. Step-by-Step Solution: List available routes: SMR/ATR, naphtha reforming, coke oven gas recovery, electrolysis.Compare primary cost drivers: electricity price dominates electrolysis OPEX.Conclude electrolysis is generally the highest-cost option in this context. Verification / Alternative check: Sectoral reports consistently show electrolysis hydrogen costs exceeding SMR-based hydrogen unless power is available at very low tariffs and high capacity factors. Why Other Options Are Wrong: COG recovery: leverages by-product gases; often economical. Naphtha and natural gas reforming: established lower-cost baselines. Fuel oil partial oxidation: typically cheaper than electrolysis on an energy basis. Common Pitfalls: Equating environmental preference with current cost; green does not always mean cheaper today, though trends are changing as renewable electricity costs decline. Final Answer: Electrolysis of water.

Question 16

Coke oven gas cooling and scrubbing: In by-product recovery at an integrated steel plant, the circulating flushing liquor used to cool and wash the hot coke oven gas is primarily composed of what?

Accepted Answer

Introduction / Context: When coal is carbonized in coke ovens, the evolved raw gas exits hot and laden with tars, ammonia, hydrogen sulfide, and other components. Immediate cooling and initial scrubbing are done using a recirculating liquid called flushing liquor to condense tars and absorb soluble components. Understanding its composition is central to by-product recovery operations and environmental control. Given Data / Assumptions: Industrial coke oven gas (COG) cooling and washing system considered. By-product recovery includes tar separation and ammonia removal. Standard practice in integrated steel plants. Concept / Approach: The circulating liquor becomes ammoniacal as it absorbs ammonia and other nitrogenous bases from the raw gas. This ammoniacal liquor is deliberately recycled through the primary coolers and scrubbers (often called the flushing liquor circuit) to enhance removal of tars and soluble gases. Downstream units then process this liquor to recover ammonia (often converted to ammonium sulfate) and to manage wastewater. Acid solutions like sulfuric or hydrochloric acid are used in specific neutralization steps elsewhere, not as the main flushing medium in the hot-gas coolers. Step-by-Step Solution: Identify function: rapidly cool and wash hot raw gas.Recognize the recirculating medium: ammoniacal liquor derived from gas washing.Select the option consistent with by-product plant practice: ammoniacal liquor. Verification / Alternative check: Process descriptions from coke oven by-product units consistently reference the ammoniacal liquor circulation loop for primary cooling and tar removal. Why Other Options Are Wrong: K2CO3 solution is used for CO2 scrubbing in some gas-treatment systems, not for primary flushing. Dilute acids are used in specific neutralization/absorption steps, not as the primary cooler liquor. Pure water alone is less effective and quickly becomes ammoniacal in service. Common Pitfalls: Assuming any water-based fluid is equivalent; the chemistry of the circulating liquor influences tar handling, corrosion, and subsequent by-product recovery. Final Answer: Ammoniacal liquor (aqueous ammonia solution from gas washing).

Question 17

In industrial fertiliser manufacture, the reaction between liquid ammonia (NH3) and 60% nitric acid (HNO3) to produce ammonium nitrate (NH4NO3) is thermally characterized as which type of reaction?

Accepted Answer

Introduction / Context: The neutralisation of nitric acid with anhydrous or aqueous ammonia to form ammonium nitrate is a key step in nitrogen fertiliser production. Correctly identifying the reaction heat effect is essential for safe reactor design, heat removal, and preventing runaway conditions in neutralisers and prilling/granulation units. Given Data / Assumptions: Reactants: liquid NH3 and ~60% HNO3. Product: ammonium nitrate solution, NH4NO3(aq). Operation commonly carried out in well-cooled neutralisers. Concept / Approach: Acid–base neutralisation reactions typically release heat. The formation of ammonium nitrate from ammonia and nitric acid is strongly exothermic, demanding vigorous heat removal to control temperature and avoid excessive vapour generation and decomposition risks downstream. Step-by-Step Solution: Recognise acid–base neutralisation: NH3 + HNO3 → NH4NO3.Recall that neutralisation enthalpies are negative (heat released).Industrial practice uses cooling coils/evaporative cooling in neutralisers, confirming significant heat evolution.Therefore, classify the reaction as exothermic. Verification / Alternative check: Plant heat balances show that substantial cooling duty is required during neutralisation, and neutraliser temperatures are tightly controlled to protect product quality and safety. Why Other Options Are Wrong: Endothermic: contradicts observed heat release. Autocatalytic: the reaction does not require self-catalysis; it is a straightforward neutralisation. None of these or reversible only at very high pressure: irrelevant to this neutralisation step. Common Pitfalls: Confusing the safe neutralisation step with the thermal stability of concentrated ammonium nitrate; decomposition hazards are separate from the neutralisation exotherm. Final Answer: exothermic

Question 18

In phosphorus processing, the conversion of yellow (white) phosphorus to red phosphorus is carried out at 250–450 °C. Under which atmosphere/condition is this transformation correctly performed in industrial retorts?

Accepted Answer

Introduction / Context: Yellow (white) phosphorus is thermodynamically less stable and more reactive than red phosphorus. Converting it to the safer, polymeric red allotrope is an important conditioning step for matches, pyrotechnics, and certain fertiliser intermediates. The operating environment (presence or absence of oxygen) critically affects both yield and safety. Given Data / Assumptions: Temperature range: 250–450 °C in retorts. Objective: allotrope conversion without oxidation/combustion. Industrial practice employs sealed vessels and inert purges. Concept / Approach: Yellow phosphorus readily oxidises in air and can ignite. The conversion to red phosphorus must therefore be performed without oxygen present—operationally described as “in the absence of air,” often implemented by an inert purge (e.g., nitrogen) to displace oxygen and moisture. Step-by-Step Solution: Identify hazard: yellow phosphorus oxidises/ignites in air.Choose safe converting environment: no oxygen present.Industrial translation: sealed retorts under inert purge or vacuum → effectively absence of air.Hence, the correct condition is the absence of air. Verification / Alternative check: Process descriptions specify inert atmospheres to prevent oxidation; this is operationally equivalent to maintaining an oxygen-free space. Why Other Options Are Wrong: Oxidising atmosphere: would oxidise/ignite phosphorus. Reducing atmosphere: unnecessary and may introduce side reactions. Steam-rich: risks hydrolysis/oxidation issues. Inert atmosphere: often used, but the core requirement tested by many MCQs is “absence of air”. Common Pitfalls: Equating “inert” strictly with nitrogen presence; the principle is preventing oxygen access, i.e., air-free conditions. Final Answer: absence of air

Question 19

Phosphate rock used in fertiliser manufacture predominantly consists of which mineral species?

Accepted Answer

Introduction / Context: Natural phosphate rock is the primary source of phosphorus for fertiliser production. Knowing its dominant mineralogy is important for selecting acidulation conditions, impurity management, and environmental controls for fluoride emissions. Given Data / Assumptions: Feed is geological “phosphate rock.” Processing routes include wet-process phosphoric acid and direct acidulation to superphosphates. Concept / Approach: Most commercial phosphate rock is a form of apatite, commonly fluorapatite (also called fluoroapatite), with idealised composition Ca5(PO4)3F or equivalently 3Ca3(PO4)2·CaF2. The fluoride in the lattice explains HF/SiF4 evolution during acidulation and the need for fluorine scrubbing. Step-by-Step Solution: Identify apatite family as dominant P-bearing minerals.Select the fluoride-bearing member: fluorapatite, Ca5(PO4)3F.Dismiss non-fertility compounds: ammonium phosphate is manufactured, not a rock mineral.Therefore, the main constituent is fluorapatite. Verification / Alternative check: Analyses of sedimentary and igneous phosphate ores consistently report fluorapatite as the principal phase, with variable substitution and impurity content. Why Other Options Are Wrong: Ammonium phosphate: synthetic fertiliser, not a rock mineral. Calcium fluoride: occurs as fluorite, not the main P carrier. Calcium phosphate (unspecified): too vague; apatite structure is the correct identification. Hydroxyapatite only: present in some ores but fluorapatite predominates. Common Pitfalls: Equating generic “calcium phosphate” with the specific apatite minerals; process design hinges on the fluoride-bearing nature of fluorapatite. Final Answer: fluorapatite (Ca5(PO4)3F)

Question 20

Ammonia synthesis converter operating window: choose the most appropriate combination of pressure and temperature used in modern Haber–Bosch converters for high conversion with viable kinetics.

Accepted Answer

Introduction / Context: Ammonia synthesis (N2 + 3 H2 ⇌ 2 NH3) is exothermic and involves a reduction in total moles. Process conditions must balance equilibrium (favours low temperature and high pressure) with kinetics (favours higher temperature). Modern converters use promoted iron or ruthenium catalysts in a defined pressure–temperature window to achieve practical rates and yields. Given Data / Assumptions: Catalysts require elevated temperature for acceptable rates. Equilibrium favours higher pressure and moderate temperature. Industrial design optimises between 150–300 atm and roughly 400–500 °C. Concept / Approach: High pressure pushes equilibrium toward ammonia (fewer moles), while very high temperature would harm equilibrium conversion despite faster kinetics. Conversely, too low a temperature slows the reaction excessively. Thus, the standard operating window sits around a few hundred atmospheres and mid-range temperatures of 400–500 °C. Step-by-Step Solution: Apply Le Chatelier’s principle: use high pressure to favour products.Choose moderate temperature: 400–500 °C balances rate and equilibrium.Reject extremes that break equilibrium (too hot) or kinetics (too cold).Therefore, select 150–300 atm and 400–500 °C. Verification / Alternative check: Published plant data and licensor information commonly report loop pressures on the order of 100–200 bar and converter inlets around 400–450 °C, with multi-bed quench or interbed cooling. Why Other Options Are Wrong: 200 atm & 1000 °C: temperature far too high; equilibrium would collapse. 450 atm & 200 °C: kinetics too slow at 200 °C. 450 atm & 550 °C: excessive temperature; equilibrium penalty. Near 1 atm & below 200 °C: impractically slow and unfavourable equilibrium. Common Pitfalls: Assuming “higher temperature is always better”; for exothermic equilibria, too much heat reduces conversion. Final Answer: about 150–300 atm and 400–500 °C

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