Question 1

Ammonia synthesis catalyst and promoter functions: In the Haber–Bosch process, a catalyst is essential because the reaction is reversible and nitrogen dissociation is difficult. What is the principal role of adding a promoter along with the catalyst?

Accepted Answer

Introduction / Context: Industrial ammonia synthesis uses an iron-based catalyst operating at elevated temperatures and pressures. Promoters—minor additives such as K2O, Al2O3, CaO, and others—are widely employed to enhance performance and durability of the catalyst. Given Data / Assumptions: Standard iron (magnetite-derived) catalyst system. Operation under typical Haber–Bosch conditions. Promoters used in conventional proportions. Concept / Approach: Promoters serve multiple roles: electronic/structural modification that boosts intrinsic activity (e.g., potassium as an electronic promoter), stabilization against sintering and poisoning, and improvement of mechanical strength and thermal robustness via structural promoters (e.g., alumina). Because all these functions are beneficial and commonly cited, the inclusive statement is correct. Step-by-Step Solution: Electronic promoters raise activity/selectivity by modifying adsorption energetics.Structural promoters enhance strength and thermal stability, resisting sintering.Collectively, promoters stabilize, strengthen, and improve effectiveness → choose 'All of the above'. Verification / Alternative check: Plant experience shows promoted catalysts maintain activity longer and tolerate thermal cycling better than unpromoted iron, confirming the multiple roles. Why Other Options Are Wrong: Each single-role option is incomplete; promoters typically deliver several benefits simultaneously. Common Pitfalls: Confusing promoters with poisons; small amounts of certain species (e.g., sulfur) are harmful, not promotional. Overlooking that overpromotion can alter pellet strength or diffusion properties. Final Answer: All of the above (a, b, and c)

Question 2

Allotropy of phosphorus in the vapor phase: At ordinary vaporization temperatures for elemental phosphorus, the vapor primarily consists of which molecular species?

Accepted Answer

Introduction / Context: Phosphorus exhibits multiple allotropes (white, red, black) and forms different gaseous species depending on temperature. Recognizing the dominant vapor species aids in understanding reactivity, toxicity, and physical properties in thermal processes. Given Data / Assumptions: Temperatures near the vaporization of white phosphorus at ambient pressure. No plasma or very high-temperature dissociation conditions. Equilibrium among gaseous phosphorus species. Concept / Approach: At moderate temperatures, phosphorus vapor is dominated by P4 molecules, reflecting the tetrahedral molecular structure of white phosphorus in the condensed phase. At much higher temperatures, dissociation to P2 and other fragments becomes significant, but under typical vaporization conditions, P4 prevails. Step-by-Step Solution: Recall the molecular form of white phosphorus: discrete P4 tetrahedra.On vaporization near its boiling point, the gas phase retains the P4 unit predominantly.Select P4 as the correct gaseous species under ordinary conditions. Verification / Alternative check: Thermodynamic data and mass spectrometry indicate P4 dominance below very high temperatures where stepwise dissociation to P2 occurs. Why Other Options Are Wrong: P, P2, and P3 require significant bond breaking or are minor at these temperatures; they become relevant only at elevated temperatures. Common Pitfalls: Confusing high-temperature dissociation products with the typical vapor species near the boiling point. Equating allotropes in solids with gas-phase speciation without considering temperature. Final Answer: P4 (tetraatomic phosphorus)

Question 3

Crop-specific nitrogen sources: For flooded paddy (rice) cultivation, which nitrogenous fertilizer is generally considered most suitable?

Accepted Answer

Introduction / Context: Choice of nitrogen fertilizer depends on soil chemistry, crop type, and water management. Paddy fields are waterlogged (anaerobic), which alters nitrogen transformations and losses. The fertilizer should minimize volatilization and fit soil pH management goals. Given Data / Assumptions: Flooded, reduced soil conditions typical of paddy fields. Objective: efficient nitrogen use with minimal gaseous losses. Common fertilizers: ammonium sulphate, CAN, ammonium nitrate, and phosphorus sources. Concept / Approach: Under submerged conditions, urea hydrolyzes to ammonium, and nitrate forms can denitrify to N2/N2O, causing losses. Ammonium sulphate provides nitrogen in the ammoniacal form less prone to immediate denitrification and also acidifies alkaline soils, which can reduce ammonia volatilization from the water surface. Therefore, ammonium sulphate is often preferred for paddy. Step-by-Step Solution: Consider nitrogen transformations in flooded soil: nitrification is limited; denitrification risk is high for nitrate.Ammonium-based fertilizers are favored over nitrate-based forms.Ammonium sulphate also helps manage high pH by supplying sulfate acidity.Choose ammonium sulphate as the most suitable option. Verification / Alternative check: Field recommendations in many rice-growing regions endorse ammonium sulphate (or split-applied urea) to reduce volatilization and denitrification losses. Why Other Options Are Wrong: CAN and ammonium nitrate supply nitrate, which is susceptible to denitrification under flooded conditions. Superphosphate is a phosphorus fertilizer, not a nitrogen source. Common Pitfalls: Ignoring soil pH; in acidic soils, ammonium sulphate can further acidify and may require liming. Assuming a single application; split dosing around crop stages improves nitrogen use efficiency. Final Answer: Ammonium sulphate

Question 4

Manufacture of ordinary superphosphate (OSP): Superphosphate fertilizer is produced industrially by reacting phosphate rock (fluorapatite) with which reagent?

Accepted Answer

Introduction / Context: Ordinary superphosphate (OSP) is a widely used phosphorus fertilizer made by acidulating phosphate rock to form water-soluble calcium dihydrogen phosphate. Identifying the correct acid is fundamental to understanding fertilizer manufacturing routes and plant design. Given Data / Assumptions: Feed: phosphate rock (largely fluorapatite, Ca10(PO4)6F2). Target product: monocalcium phosphate with gypsum byproduct. Single-acid process for OSP (not triple superphosphate). Concept / Approach: In the OSP process, phosphate rock reacts with sulphuric acid to form monocalcium phosphate monohydrate (water-soluble P) and calcium sulphate (gypsum). For triple superphosphate, phosphoric acid is used instead. Organic acids like acetic acid are too weak and impractical; Lewis acids such as AlCl3 are not used for this purpose. Step-by-Step Solution: Balanced overall reaction (idealized): Ca3(PO4)2 + 2 H2SO4 + 4 H2O → Ca(H2PO4)2·H2O + 2 CaSO4·2H2O.Sulphuric acid provides the sulfate and protons required to convert rock phosphate to soluble mono-calcium phosphate.Therefore, choose 'Sulphuric acid'. Verification / Alternative check: Industrial practice distinguishes OSP (H2SO4 route) from triple superphosphate (H3PO4 route), confirming the correct acid here. Why Other Options Are Wrong: Acetic acid cannot effectively convert apatite; AlCl3 is irrelevant; 'None of these' is false because the correct reagent is listed. Common Pitfalls: Confusing OSP with TSP and selecting phosphoric acid; OSP specifically uses sulphuric acid. Overlooking gypsum handling as a major byproduct management issue. Final Answer: Sulphuric acid

Question 5

Physical form of commercial fertilizers: In large-scale agricultural distribution and field application, commercial fertilizers are predominantly supplied in which physical form?

Accepted Answer

Introduction / Context: The physical form of fertilizers affects handling, storage stability, dusting, caking, and application accuracy with spreaders or planters. Modern supply chains favor forms that flow well and maintain uniform nutrient distribution. Given Data / Assumptions: Bulk transport and field spreading using mechanical applicators. Hygroscopicity and caking tendencies considered. User preference for minimal dust and even field coverage. Concept / Approach: Granulated fertilizers offer superior flowability, reduced dust, minimized segregation in blends, and better resistance to caking compared with powders. Lumps and flakes are undesirable for uniform application and can clog equipment. Therefore, granules are the predominant commercial form across nitrogen, phosphorus, and potassium products and blends (NPKs). Step-by-Step Solution: Compare handling: granules > powders in dust control and flow.Assess application: granules spread evenly from centrifugal spreaders.Conclude that granules are the standard market form.Select 'Granules'. Verification / Alternative check: Industry specifications (e.g., size guide number, SGN) define granule sizing for predictable spread patterns, confirming predominance of granules. Why Other Options Are Wrong: Powders dust and segregate; lumps/flakes indicate poor conditioning or caking and are unsuitable for precision application. Common Pitfalls: Assuming powdered micronutrients imply powders are typical; they are often granulated or prilled for blends. Confusing prills and granules—both are granular forms acceptable for spreading. Final Answer: Granules

Question 6

Industrial urea synthesis — Urea is formed only under which physical condition of the reacting mixture (ammonia + carbon dioxide via ammonium carbamate)? Choose the most accurate statement about the phase in which urea actually forms in commercial h…

Accepted Answer

Introduction: Modern urea plants synthesize urea from ammonia and carbon dioxide in two steps: fast formation of ammonium carbamate followed by its dehydration to urea and water. Understanding the phase in which urea actually forms is vital for reactor design, conversion control, and corrosion/energy considerations. Given Data / Assumptions: Synthesis loop operates typically at 140–200 bar and about 170–200°C. Reaction mixture is a concentrated aqueous solution of NH3, CO2, and ammonium carbamate. No catalytic solid bed is employed; contacting is liquid-phase. Concept / Approach: Step 1: NH3 + CO2 → NH2COONH4 (ammonium carbamate) is rapid and exothermic in solution. Step 2: NH2COONH4 → NH2CONH2 + H2O (urea + water) is reversible and relatively slow, proceeding in the liquid medium. Gas-phase urea formation is negligible under practical conditions because the concentrations and collision efficiency required are not met; instead, the high-pressure liquid solution provides intimate molecular contact and solvates ionic intermediates. Step-by-Step Solution: Recognize the synthesis loop is a high-pressure liquid solution.Identify that both carbamate formation and dehydration proceed in this liquid phase.Conclude: urea forms only in the liquid phase in commercial practice. Verification / Alternative check: Process flow diagrams show liquid-phase reactors/strippers with recirculated aqueous ammonia and carbamate; no gas-phase reactor is used. Equilibrium/kinetic models are expressed for liquid compositions and activities. Why Other Options Are Wrong: Vapour phase: impractical and not used; conversion would be negligible. Very high temperature alone does not ensure formation and can destabilize the system. Vacuum is used in downstream concentration, not in synthesis. Solid-state reaction does not describe the commercial route. Common Pitfalls: Confusing downstream evaporation/concentration (often under vacuum) with the synthesis step; assuming “gas synthesis” like ammonia applies here. Final Answer: In liquid phase (high-pressure solution)

Question 7

Ammonia (NH₃) synthesis gas from natural gas — Which primary process step generates the H₂-rich make-up gas fed to the Haber–Bosch loop?

Accepted Answer

Introduction: Ammonia manufacture requires a hydrogen-rich synthesis gas combined with nitrogen at about 3:1 molar ratio. For natural-gas–based plants, the front-end process determines efficiency, CO₂ capture load, and impurity control. Given Data / Assumptions: Feedstock: natural gas (primarily methane). Target: H₂ + N₂ mixture for Haber–Bosch loop. Standard industrial practice considered. Concept / Approach: Steam reforming converts methane with steam to synthesis gas: CH4 + H2O ⇌ CO + 3H2 (endothermic). A water–gas shift then increases H₂: CO + H2O ⇌ CO2 + H2. CO₂ is removed, and residual CO/CO₂ are further decreased (e.g., methanation) before compression and mixing with N₂ (from air separation or secondary reformer). Partial oxidation is used in heavy-oil routes or as an autothermal variant, but classical natural-gas plants rely on steam reforming as the primary step. Step-by-Step Solution: Identify NG front-end → primary steam reformer.Apply shift conversion to raise H₂ and convert CO to CO₂.Remove CO₂ and polish impurities; send H₂ to synthesis loop with N₂. Verification / Alternative check: Block flow diagrams of ammonia plants universally show primary steam reforming followed by shift, CO₂ removal, and methanation when natural gas is the feed. Why Other Options Are Wrong: Thermal cracking yields unsaturated hydrocarbons/soot and insufficient H₂. Partial oxidation alone is not typical for NG (autothermal combines both but still includes reforming chemistry). Hydrogenation of CO₂ produces methane, not NH₃ syngas. Electrolysis is unrelated to NG reforming route. Common Pitfalls: Confusing autothermal reforming with pure POX; assuming the nitrogen source is from the front-end rather than air addition later. Final Answer: Steam reforming of natural gas (followed by shift and purification)

Question 8

Thermal dehydration of phosphoric acids — Heating orthophosphoric acid (H₃PO₄) to about 250°C chiefly produces which condensed phosphoric acid?

Accepted Answer

Introduction: Phosphoric acids undergo stepwise condensation upon heating, forming P–O–P linkages and releasing water. Recognizing which species forms at a given temperature is important in fertilizer and phosphate processing. Given Data / Assumptions: Starting acid: orthophosphoric acid, H3PO4. Temperature around 250°C. Closed system without significant decomposition to other oxyacids. Concept / Approach: Upon heating, two molecules of H3PO4 condense: 2 H3PO4 → H4P2O7 + H2O, giving pyrophosphoric (diphosphoric) acid. At still higher temperatures and with prolonged dehydration, polyphosphoric and finally metaphosphoric acids (general formula HPO3)n can form. But near 250°C, the predominant product is H4P2O7. Step-by-Step Solution: Write the condensation: 2 H3PO4 → H4P2O7 + H2O.Match temperature regime: ≈200–300°C favors diphosphoric acid.Conclude that pyrophosphoric acid is produced. Verification / Alternative check: Process texts on phosphate fertilizers describe controlled dehydration steps, with pyrophosphate formation preceding metaphosphate formation at higher temperature. Why Other Options Are Wrong: Metaphosphoric acid typically forms at higher temperature/greater dehydration. “No change” contradicts known dehydration behavior. Phosphorous acid is a different oxyacid obtained by other routes, not thermal dehydration of H3PO4. Common Pitfalls: Confusing orthophosphoric dehydration series; mixing up phosphoric (H3PO4) and phosphorous (H3PO3) acids. Final Answer: Pyrophosphoric acid (H₄P₂O₇)

Question 9

Fertilizer classification — Calcium ammonium nitrate (CAN) is best classified as which type of fertilizer product?

Accepted Answer

Introduction: Calcium ammonium nitrate (CAN) is a widely used nitrogenous fertilizer. Correct classification helps agronomists communicate nutrient planning and assess storage/handling requirements. Given Data / Assumptions: CAN contains ammonium nitrate blended with powdered limestone or dolomite. Primary plant nutrients are N, P, K. Secondary include Ca, Mg, S. Calcium content improves handling and reduces explosion risk versus pure ammonium nitrate. Concept / Approach: A straight fertilizer supplies only one primary nutrient. CAN provides nitrogen as its primary nutrient; calcium (and sometimes magnesium) are secondary nutrients and do not change the classification to “mixed,” which requires at least two of N, P, K. CAN is therefore a straight nitrogenous fertilizer. Step-by-Step Solution: Identify primary nutrient(s) supplied: nitrogen only.Recognize calcium is a secondary nutrient; presence does not make it “mixed.”Classify CAN accordingly as a straight fertilizer. Verification / Alternative check: Extension bulletins and fertilizer regulations list CAN under straight nitrogen fertilizers, distinct from NPK complexes or blends. Why Other Options Are Wrong: Mixed fertilizer requires at least two of N, P, K. Complex fertilizer refers to chemically combined multi-nutrient salts (e.g., diammonium phosphate), not CAN. “Not a fertilizer” is false; CAN is a common agricultural N source. It is not a biofertilizer. Common Pitfalls: Confusing presence of secondary nutrients with “mixed”; conflating CAN with ammonium nitrate hazards. Final Answer: A straight fertilizer (supplies a single primary nutrient, nitrogen)

Question 10

Urea synthesis chemistry — The dehydration of ammonium carbamate to urea is best described as which type of reaction?

Accepted Answer

Introduction: In the urea process, the second step converts ammonium carbamate to urea and water. Recognizing the heat effect and equilibrium nature informs heat integration and reactor/stripper design. Given Data / Assumptions: Step 1 (formation of carbamate) is rapid and strongly exothermic. Step 2 (dehydration to urea) proceeds more slowly and is reversible. Operating at high pressure and moderate temperature in liquid phase. Concept / Approach: The dehydration reaction NH2COONH4 ⇌ NH2CONH2 + H2O absorbs heat (endothermic). Higher temperatures favor urea formation but also increase corrosion and side reactions; pressure and NH3/CO2 ratios influence equilibrium by affecting activities. No solid catalyst is used; kinetics depend on solution composition and temperature. Step-by-Step Solution: Write reaction: ammonium carbamate → urea + water.Identify heat effect: endothermic (requires heat input).Acknowledge reversibility: equilibrium-limited; stripping removes CO2/NH3 to shift conversions. Verification / Alternative check: Energy balances in plant design allocate heat to the reactor/stripper to sustain dehydration; coolant duty is assigned to the upstream exothermic carbamate formation. Why Other Options Are Wrong: “Catalytic” is incorrect; no solid catalyst is employed. “Exothermic” swaps the heat effect with step 1. “Reversible only” misses the heat effect; while reversible, the key classification here is endothermic. Not spontaneous at ambient conditions. Common Pitfalls: Conflating the heat effects of the two sequential reactions; assuming catalysts are required because many synthesis processes are catalytic. Final Answer: Endothermic (heat is absorbed; equilibrium-limited)

Question 11

Phosphate rock acidulation — Reaction of phosphate rock with dilute sulphuric acid produces which fertilizer product?

Accepted Answer

Introduction: Phosphate fertilizers are produced by acidulating phosphate rock (apatite). The choice of acid and its strength determines whether the main product is phosphoric acid, single superphosphate, or triple superphosphate. Given Data / Assumptions: Feed: phosphate rock, mainly apatite (Ca10(PO4)6F2 and related). Acid: dilute H2SO4. Conventional wet-process acidulation at ambient to moderate temperature. Concept / Approach: With dilute sulphuric acid, the principal reaction yields monocalcium phosphate monohydrate in the presence of gypsum: Ca3(PO4)2 + 2 H2SO4 + 4 H2O → Ca(H2PO4)2·H2O + 2 CaSO4·2H2O. The resulting product is called single superphosphate (SSP), a mixture of monocalcium phosphate and gypsum. When phosphoric acid, not dilute sulphuric acid, is used, the product is triple superphosphate (TSP) with higher P2O5 content. Step-by-Step Solution: Identify acidulating agent: dilute H2SO4.Write net reaction giving monocalcium phosphate + gypsum.Recognize product trade name: single superphosphate. Verification / Alternative check: Fertilizer manuals specify SSP production by sulphuric acid attack; TSP requires phosphoric acid. Why Other Options Are Wrong: Phosphoric acid is produced by stronger acidulation routes, not by dilute H2SO4 on rock alone. TSP needs H3PO4, not H2SO4. Gypsum is a byproduct with SSP, not the sole product. MAP requires ammonia and phosphoric acid, a separate neutralization step. Common Pitfalls: Interchanging SSP and TSP processes; overlooking gypsum’s presence in SSP. Final Answer: Single superphosphate (SSP)

Question 12

Water in the urea reactor — During conversion of ammonium carbamate to urea, what is the effect of a large excess of water in the reacting solution?

Accepted Answer

Introduction: The urea synthesis liquid contains NH3, CO2, ammonium carbamate, water, and urea. Water plays a dual role: it is a product of dehydration and a solvent. However, too much water negatively affects the equilibrium conversion to urea. Given Data / Assumptions: Liquid-phase reversible dehydration: NH2COONH4 ⇌ NH2CONH2 + H2O. High pressure, moderate temperature; downstream stripping/evaporation present. Activity effects: higher water concentration shifts equilibrium. Concept / Approach: Le Châtelier’s principle applies: since water is a product, adding excess water drives the equilibrium back toward ammonium carbamate, lowering urea yield at a given temperature and pressure. Moreover, excess water increases the duty of downstream concentrators and can slow kinetics by dilution. Plants therefore control water balance and use high NH3/CO2 ratios and stripping to enhance conversion. Step-by-Step Solution: Consider equilibrium: adding product (water) shifts left.Assess process impact: more water → lower conversion, higher evaporation duty.Conclude that large excess water adversely affects yield. Verification / Alternative check: Simulation and plant data show conversion drops with higher water content at fixed T, P, and NH3/CO2, validating the adverse effect. Why Other Options Are Wrong: Increasing yield would require removal of water/volatile components, not addition. “No yield penalty” ignores equilibrium and kinetic dilution effects. Corrosion mitigation is separate and does not inherently raise conversion. Common Pitfalls: Assuming dilution always helps reactions; overlooking that water is a reaction product here. Final Answer: It adversely affects (reduces) the yield of urea

Question 13

Indian fertilizer plants — A plant manufacturing ammonium sulphate by the gypsum–ammonia route (instead of the usual direct sulphuric acid neutralization) is located at which of the following sites?

Accepted Answer

Introduction: Ammonium sulphate can be produced by several routes: neutralization of ammonia with sulphuric acid, recovery from coke-oven gas, caprolactam byproduct, or reaction of gypsum with ammonia and carbon dioxide. Historical plant locations in India reflect raw-material availability and integration with steel or chemical complexes. Given Data / Assumptions: Question refers to the gypsum–ammonia process. Sites listed include steel-associated and fertilizer corporation locations. Historical context of public-sector plants. Concept / Approach: The gypsum–ammonia route converts CaSO4·2H2O with NH3 and CO2 (from calcination/limestone or other sources) into (NH4)2SO4 and CaCO3. In India, the Sindri unit of the Fertilizer Corporation of India (FCI) is classically associated with diversified fertilizer manufacture and has been cited with ammonium sulphate production including non-conventional routes. Step-by-Step Solution: Identify which option corresponds to an FCI fertilizer complex historically noted for AS production.Select Sindri (under FCI).Other sites are primarily steel or different chemical complexes not noted for the gypsum–ammonia route. Verification / Alternative check: Industry references on legacy Indian fertilizer plants attribute gypsum–ammonia AS manufacture to Sindri operations in specific periods, distinguishing it from caprolactam byproduct AS at Baroda (GSFC) or coke-oven recovery at steel plants. Why Other Options Are Wrong: Rourkela/Bokaro: steel plants where AS would more likely be byproduct from coke-oven gas. Baroda (GSFC): associated with caprolactam byproduct AS, not gypsum–ammonia as the main route. Vizag: not the canonical example for the gypsum–ammonia AS route. Common Pitfalls: Assuming all AS is made by direct acid neutralization; overlooking historical process diversity tied to local feedstocks. Final Answer: Sindri (under FCI)

Question 14

Plant nutrients — Which of the following is NOT classified as a secondary nutrient for plant growth?

Accepted Answer

Introduction: Essential plant nutrients are grouped by the quantities required: primary (N, P, K), secondary (Ca, Mg, S), and micronutrients (Fe, Mn, Zn, Cu, B, Mo, Cl, Ni). Differentiating among these categories is fundamental to fertilizer formulation and soil testing. Given Data / Assumptions: Primary macronutrients: nitrogen, phosphorus, potassium. Secondary macronutrients: calcium, magnesium, sulphur. Non-mineral elements like carbon, hydrogen, oxygen are obtained largely from air and water. Concept / Approach: Secondary nutrients are supplied via soil amendments and fertilizers when deficient. Oxygen is essential for life but is not classified as a mineral plant nutrient in fertilizer practice; plants obtain O (and H) primarily from water and CO2, not as a separate fertilizer nutrient category. Step-by-Step Solution: List secondary nutrients: Ca, Mg, S.Compare with options; identify oxygen as not on the secondary list.Select oxygen as the correct “NOT” answer. Verification / Alternative check: Agronomy guides and fertilizer labels enumerate secondary nutrients explicitly as Ca, Mg, and S. Why Other Options Are Wrong: Calcium, magnesium, sulphur are standard secondary nutrients. “None” is incorrect because oxygen is not in that category. Common Pitfalls: Confusing essentiality with classification; all 17 essential elements are necessary, but categories depend on required amounts and fertilizer practice. Final Answer: Oxygen (O)

Question 15

Pick the wrong statement about phosphorus and nitrogen products — Identify the statement that is NOT correct.

Accepted Answer

Introduction: Handling and classification of fertilizer materials depend on accurate chemical knowledge—from allotropes and mineral compositions to storage properties like hygroscopicity. This question asks you to spot the erroneous statement among commonly cited facts. Given Data / Assumptions: Yellow (white) phosphorus is highly reactive and pyrophoric. Apatite is the main mineral form of phosphate rock used for phosphorus processing. Urea and ammonium nitrate are both nitrogen fertilizers with different physical properties. Nitrogen fixation includes industrial (Haber–Bosch) and biological pathways. Concept / Approach: Statements (a), (b), and (d) are established facts: yellow/white phosphorus is indeed shipped under water; apatite’s general formula is Ca10(PO4)6(F,Cl,OH); nitrogen fixation is the conversion of N2 into combined forms like NH3 or organic nitrogen. The questionable statement is about hygroscopicity: ammonium nitrate is markedly more hygroscopic than urea and can absorb moisture to form sticky or liquefied masses, whereas urea is hygroscopic but significantly less so. Step-by-Step Solution: Evaluate each statement against standard references.Confirm (a), (b), (d) as correct.Identify (c) as incorrect because ammonium nitrate, not urea, is the more hygroscopic material. Verification / Alternative check: Material safety data and fertilizer handbooks rank AN as highly hygroscopic and prone to caking; urea is moderate and can be granulated with conditioners to improve storage. Why Other Options Are Wrong: (a) True: water immersion prevents ignition/oxidation. (b) True: formula represents fluorapatite/hydroxylapatite family. (d) True: definition covers biological and industrial fixation. (e) False because (c) is incorrect. Common Pitfalls: Assuming all nitrogen fertilizers behave similarly in storage; overlooking the severe caking and moisture uptake issues with ammonium nitrate. Final Answer: Urea is more hygroscopic than ammonium nitrate

Question 16

Industrial gas purification — What is the Vetrocoke solution used for acid-gas (CO2/H2S) absorption composed of?

Accepted Answer

Introduction: Vetrocoke (also known from the Giammarco–Vetrocoke process) is a classic chemical absorption solvent used in gas purification plants to remove acidic gases such as carbon dioxide and hydrogen sulfide from synthesis gas and refinery streams. Knowing the exact composition helps distinguish it from other hot carbonate or amine systems. Given Data / Assumptions: Question asks specifically for the composition of the Vetrocoke solution. Context is acid-gas removal in syngas processing and ammonia/urea plants. We compare with other families: hot carbonate (Benfield), amines (MEA/DEA), and alkaline salts. Concept / Approach: Vetrocoke is based on aqueous potassium carbonate (K2CO3) and historically included arsenic trioxide (As2O3) as a promoter/inhibitor package to enhance absorption kinetics and suppress catalyst poisoning/foaming. This differentiates it from the Benfield process (K2CO3 activated with amines like DEA or piperazine) and from primary/secondary amine systems like MEA/DEA which contain no carbonate salt as the primary base. Step-by-Step Solution: Identify the named solvent family: Vetrocoke.Recall its formulation: aqueous K2CO3 + As2O3 as promoter.Eliminate look-alikes (Na2CO3 + As2O3 is not Vetrocoke; sulfate salts are unrelated).Conclude the correct composition is K2CO3 with As2O3. Verification / Alternative check: Process design references list Vetrocoke as potassium carbonate with arsenic trioxide additives, whereas Benfield is potassium carbonate with organic amine activators. Plant licensing literature preserves this distinction historically. Why Other Options Are Wrong: B/D: Sulfates (K2SO4, Na2SO4) are neutral salts, not absorption solvents. C: Sodium carbonate with arsenic is not the named Vetrocoke formulation. E: Amine-activated hot carbonate exists (Benfield), but that is not Vetrocoke. Common Pitfalls: Confusing Vetrocoke with other hot carbonate technologies; always check the promoter package and base salt identity. Final Answer: a mixture of K2CO3 and As2O3

Question 17

Fertilizer fundamentals — Which statement about ammonium sulfate [(NH4)2SO4] fertilizer is most accurate for agronomic use?

Accepted Answer

Introduction: Ammonium sulfate [(NH4)2SO4] is a widely used nitrogenous fertilizer supplying both nitrogen and sulfur. Understanding its agronomic niche versus alternatives like urea or ammonium nitrate helps in crop-specific recommendations, especially for flooded rice (paddy) systems. Given Data / Assumptions: Comparison of form, analysis, and soil reaction among common N fertilizers. Paddy fields are typically flooded and slightly reduced (low-oxygen) environments. Sulfur nutrition can be limiting in some soils; sulfate provides readily available S. Concept / Approach: Ammonium sulfate is an ammoniacal fertilizer that acidifies soils over time due to nitrification of NH4+ to NO3− releasing H+. In flooded paddy, the ammonium form is retained better (less leaching) and is plant-preferred under reduced conditions. It also supplies sulfate-sulfur, which benefits many cereals including rice. Although urea has a higher N concentration (46% N), ammonium sulfate’s agronomic behavior often makes it a recommended choice for paddy where S is needed and volatilization losses can be managed. Step-by-Step Solution: Identify key crop: paddy (rice) under flooded conditions.Recognize NH4+ is stable under reduction and readily taken up by rice.Note added benefit of sulfate-S from ammonium sulfate.Conclude it is commonly regarded as a good/'best' fit for paddy relative to the listed statements. Verification / Alternative check: Agronomy guides often list ammonium sulfate as suitable for rice, especially where sulfur deficiency is present. By contrast, urea is the highest concentration N source, not ammonium sulfate. Why Other Options Are Wrong: A: Incorrect; urea (46% N) is higher concentration. C/D: It is acid-forming, not basic or neutral. E: It is not urea-based and is not primarily a slow-release product. Common Pitfalls: Assuming highest N concentration automatically means best agronomic fit—crop and soil conditions determine suitability. Final Answer: the best fertiliser for paddy

Question 18

Syngas purification — In naphtha steam reforming, the CO2 present in the reformed gas is typically removed by absorption into which solvent?

Accepted Answer

Introduction: Steam reforming of naphtha produces a synthesis gas containing H2, CO, CO2, CH4, and impurities. Downstream processes (e.g., ammonia synthesis) require CO2 removal to protect catalysts and meet composition targets. Identifying the standard solvent is a core process design decision. Given Data / Assumptions: Post-shift gas contains significant CO2. Solvent absorption is used prior to methanation or cryogenic steps. Common industrial choices include amines and hot carbonate systems. Concept / Approach: MEA (monoethanolamine) is a primary amine widely used for chemical absorption of CO2 via reversible carbamate/bicarbonate formation. It offers fast kinetics and established regeneration practice. Alternatives like hot potassium carbonate, DEA, MDEA, or physical solvents may also be used, but in many classical plant designs the baseline answer is MEA. Slaked lime is suited to fixed chemical scrubbing and not standard for continuous syngas purification; ammoniacal liquor and MEK are not mainstream CO2 solvents in reformer trains. Step-by-Step Solution: Identify need: remove CO2 from shifted reformate.Recall standard solvents: MEA/DEA/MDEA or K2CO3.Of listed options, MEA is the conventional choice for absorption-regeneration loops.Therefore select MEA. Verification / Alternative check: Process schematics for ammonia plants show amine absorbers and strippers in the CO2 removal section, with MEA or DEA commonly specified. Why Other Options Are Wrong: B: Lime would produce solids and is unsuitable for cyclic solvent systems. C: Ammoniacal liquor is not a standard CO2 solvent here. D: MEK is an organic solvent, not used for CO2 chemical absorption. E: Propylene carbonate is a physical solvent used at high pressures; not the canonical answer versus MEA. Common Pitfalls: Overlooking that solvent selection depends on pressure and composition; MEA remains a standard textbook answer. Final Answer: mono-ethanolamine (MEA)

Question 19

Fertilizer additives — Why are conditioners such as finely divided peat added to granular fertilizers during manufacture and storage?

Accepted Answer

Introduction: Granular fertilizers can absorb moisture and undergo physical changes during handling and storage, leading to caking, hardening, and poor flowability. Conditioners are minor additives used to maintain product integrity and ensure consistent field application. Given Data / Assumptions: Finely divided peat is cited as a representative conditioner (others include clays, talc, or lignite). Focus is on physical handling properties, not nutrient chemistry. Granular products are stored in bags or silos under varying humidity. Concept / Approach: Conditioners act as moisture scavengers, anti-caking agents, or surface coatings to reduce inter-granular bridges formed by dissolved–recrystallized salts. By interrupting crystal growth and minimizing liquid bridges, they prevent hard agglomerates, keeping fertilizers free-flowing. They do not materially increase nutrient content or significantly alter solubility or pH. Step-by-Step Solution: Identify the problem: caking/hardening during storage and transport.Select a mitigation: add a conditioner (e.g., peat) to disrupt crystal bridges and absorb moisture.Evaluate outcomes: improved flow, reduced lumps, consistent spreading.Thus, the purpose is to avoid caking and hardening. Verification / Alternative check: Fertilizer quality standards specify anti-caking additives and coating oils to maintain flow; industry practice confirms their effectiveness. Why Other Options Are Wrong: A: Burning relates to foliar application rates, not storage. C: Bulking without purpose adds cost. D: Solubility is governed by salt chemistry, not conditioners. E: Peat does not reliably raise pH. Common Pitfalls: Confusing anti-caking conditioners with nutrient coatings (e.g., sulfur or polymer for controlled release). Final Answer: to avoid caking and hardening

Question 20

Ammonia–urea complexes — Industrial fertilizer plants meet their nitrogen (N2) requirement primarily by obtaining nitrogen via which route?

Accepted Answer

Introduction: Nitrogen is the primary feed for ammonia synthesis (Haber–Bosch), which underpins the global fertilizer industry. Large-scale, reliable supply of high-purity N2 is essential. Understanding the standard industrial source clarifies front-end integration in ammonia–urea complexes. Given Data / Assumptions: High-purity nitrogen is required continuously at significant flow rates. Co-product oxygen may be valuable but is not mandatory. Plant scales are typically hundreds to thousands of tonnes per day of NH3. Concept / Approach: The standard source of nitrogen for large fertilizer complexes is cryogenic air separation units (ASU), which liquefy and distill air to supply N2 (and often O2/Ar). Alternative sources such as decomposition of NOx or recovery from process gases are impractical or insufficient. Membranes can supply moderate-purity nitrogen for inerting, not typically for ammonia synthesis where high purity is demanded to avoid catalyst poisoning. Step-by-Step Solution: Identify demand: high-purity, high-flow N2 for NH3 synthesis.Match technology: cryogenic distillation of air is proven and economical at scale.Eliminate alternatives that lack capacity or purity.Select cryogenic fractionation of liquefied air. Verification / Alternative check: Process flow diagrams for ammonia plants routinely show an ASU or purchase of pipeline nitrogen produced cryogenically. Why Other Options Are Wrong: B: Dissociating NOx is not an industrial nitrogen source. C/D: Producer/coke-oven gases do not provide bulk, pure N2. E: Membranes are typically for lower-purity inerting, not synthesis-grade nitrogen. Common Pitfalls: Assuming small packaged nitrogen generators (membranes/PSA) can meet the purity/flow needed for ammonia synthesis—these are rarely suitable for base-load NH3 plants. Final Answer: fractionation (cryogenic distillation) of liquefied air

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