Question 1

Phosphate fertilizers — The typical P2O5 content in triple superphosphate (TSP) is approximately what percentage range?

Accepted Answer

Introduction: Triple superphosphate (TSP) is a concentrated phosphate fertilizer produced by reacting phosphate rock with phosphoric acid. Its nutrient analysis is commonly expressed as percent P2O5, a conventional oxide basis used in fertilizer trade and labeling. Given Data / Assumptions: TSP consists largely of monocalcium phosphate monohydrate. Commercial grades are standardized within a narrow range. Percentages refer to mass percent P2O5 equivalent. Concept / Approach: Typical TSP grades are around 46% P2O5, often labeled as 0–46–0. Therefore, the acceptable range encapsulating most commercial product is about 42–50% P2O5. Lower ranges (15–20%) correspond to single superphosphate (SSP), while extremely high numbers (70%+) are unrealistic for bulk fertilizers and would imply purified phosphate chemicals rather than granular fertilizers. Step-by-Step Solution: Recall commercial grade: TSP ≈ 46% P2O5.Match to the listed ranges → 42–50%.Eliminate alternatives inconsistent with market grades.Select the correct range. Verification / Alternative check: Fertilizer specifications and datasheets list TSP at approximately 46% P2O5 with minor impurities and conditioning agents. Why Other Options Are Wrong: B: SSP range; C/D: unrealistically high for commercial TSP; E: too low for TSP. Common Pitfalls: Confusing total P with P2O5 equivalent or mixing up SSP and TSP typical analyses. Final Answer: 42–50

Question 2

Haber–Bosch promoter package — Identify a catalyst promoter used in catalytic ammonia synthesis over iron.

Accepted Answer

Introduction: Industrial ammonia synthesis employs an iron-based catalyst containing multiple promoters that enhance activity, stability, and resistance to poisons. Recognizing common promoters is a fundamental aspect of catalytic process knowledge. Given Data / Assumptions: Base catalyst: magnetite-derived iron reduced in situ. Promoters include alkali/alkaline species for electronic promotion and oxides for structural stability. Operating conditions: ~400–500°C, 100–250 bar, H2:N2 ≈ 3:1. Concept / Approach: Potassium oxide (K2O) is a classic electronic promoter for iron in the Haber–Bosch process, increasing the electron density at active sites and improving N2 dissociation. While alumina (Al2O3) is often present as a structural/textural promoter, the most commonly cited specific activity promoter is K2O. Chromium oxide and manganese oxide are not standard promoters in modern iron ammonia catalysts; silica may be used in traces as a structural additive but is not the prime electronic promoter. Step-by-Step Solution: Recall promoter roles: electronic (alkali) and structural (alumina/calcia).Identify K2O as the key alkali promoter enhancing activity.Eliminate oxides not typical for modern NH3 iron catalysts.Choose K2O. Verification / Alternative check: Commercial catalyst specs (e.g., magnetite with K, Al, Ca promoters) corroborate the prominent role of K2O. Why Other Options Are Wrong: A: Al2O3 is mainly a structural promoter; the question emphasizes activity promotion. B/D: Not standard for Haber–Bosch iron catalysts today. E: SiO2 is not the principal promoter for activity. Common Pitfalls: Confusing structural supports with electronic promoters; both exist but play different roles. Final Answer: K2O

Question 3

Industrial organics — The compound with formula (CH3·C6H4)3PO4 is known as:

Accepted Answer

Introduction: Recognizing chemical names from condensed formulas is a common test of industrial chemistry literacy. The notation (CH3·C6H4) indicates a cresyl (methylphenyl) group, and three such groups bonded to phosphate yield a well-known plasticizer and flame retardant additive. Given Data / Assumptions: (CH3·C6H4) denotes a cresyl group (o-, m- or p- isomers). Three aryl groups attach to a phosphate center (PO4). Inorganic phosphate fertilizers have different stoichiometry and are solids of calcium phosphate salts. Concept / Approach: Tricresyl phosphate (TCP) is an aryl phosphate ester derived from cresols. Its general formula can be written as (cresyl)3PO4, matching (CH3·C6H4)3PO4. By contrast, triple superphosphate/superphosphate and fluorapatite are inorganic calcium phosphate materials and do not have aryl groups. Triphenyl phosphate would be (C6H5)3PO4, lacking the methyl substituents present in cresyl groups. Step-by-Step Solution: Parse the formula: three cresyl groups attached to phosphate.Map to compound name: tricresyl phosphate.Eliminate inorganic fertilizers and the phenyl (not cresyl) analogue.Answer: tricresyl phosphate. Verification / Alternative check: Industrial datasheets list TCP as (cresyl)3PO4; TPP is (phenyl)3PO4, confirming the naming distinction. Why Other Options Are Wrong: A/D/C: Inorganic calcium phosphate fertilizers/minerals, not aryl phosphates. E: Triphenyl phosphate lacks methyl substituents on the phenyl rings. Common Pitfalls: Overlooking that fertilizer names with 'superphosphate' refer to calcium phosphate salts, not organophosphates. Final Answer: tricresyl phosphate

Question 4

Haber process — Which catalyst is used industrially for ammonia (NH3) synthesis?

Accepted Answer

Introduction: The classical Haber–Bosch process continues to produce the majority of world ammonia using iron-based catalysts. While alternative catalysts exist (e.g., ruthenium on carbon), the industry standard remains magnetite-derived iron reduced to an active metallic phase with promoters. Given Data / Assumptions: Synthesis loop conditions: 100–250 bar, 400–500°C. Catalyst prepared from Fe3O4 precursor and promoters (K2O, Al2O3, CaO). Feed gas is purified H2/N2 at about 3:1 molar ratio. Concept / Approach: Commercial catalysts are supplied as promoted iron oxides (magnetite) that are reduced in situ to active metallic iron while retaining promoter distribution. Nickel is primarily used for steam reforming/methanation, vanadium pentoxide for SO2 oxidation, and silica gel is a desiccant not a synthesis catalyst. Although ruthenium-on-carbon catalysts have been deployed in some high-pressure loops, the canonical and most widely used answer is reduced iron oxide. Step-by-Step Solution: Identify the process: ammonia synthesis (Haber–Bosch).Recall industry-standard catalyst: promoted iron derived from oxidic precursor.Eliminate catalysts associated with other processes (Ni for reforming, V2O5 for sulfuric acid).Select reduced iron oxide. Verification / Alternative check: Plant licensor literature and textbooks consistently list promoted Fe as the mainstream catalyst for NH3 synthesis. Why Other Options Are Wrong: B: Nickel is not the standard NH3 synthesis catalyst. C: V2O5 is for SO2 → SO3. D: Silica gel is an adsorbent. E: Ru/C exists but is not the widely adopted baseline in general question contexts. Common Pitfalls: Confusing catalysts from front-end reforming/methanation with the back-end synthesis loop. Final Answer: reduced iron oxide

Question 5

By-product route — Ammonium sulfate [(NH4)2SO4] can be produced industrially by reacting gypsum (CaSO4·2H2O) with which reagent under appropriate conditions?

Accepted Answer

Introduction: Ammonium sulfate is manufactured both as a primary product and as a by-product in caprolactam and coke-oven processes. One classical route uses natural gypsum as a sulfur source, forming ammonium sulfate while precipitating calcium carbonate—an attractive utilization of mineral by-products. Given Data / Assumptions: Starting solid: gypsum (CaSO4·2H2O). Goal: produce (NH4)2SO4 in aqueous media. Carbonate availability via ammonium carbonate or via NH3 + CO2 + H2O generating (NH4)2CO3 in situ. Concept / Approach: The net reaction proceeds effectively when ammonium carbonate reacts with gypsum to yield ammonium sulfate and calcium carbonate: CaSO4·2H2O + (NH4)2CO3 → (NH4)2SO4 + CaCO3 + 2H2O. In practice, NH3 and CO2 are sparged into a gypsum slurry to form ammonium carbonate in situ, which then drives the conversion. Direct reaction with NH3 alone is insufficient; nitric acid would produce calcium nitrate rather than target ammonium sulfate. Step-by-Step Solution: Write the stoichiometry with ammonium carbonate and gypsum.Confirm products: (NH4)2SO4 in solution and CaCO3 precipitate.Note practical implementation: in situ formation of (NH4)2CO3 using NH3 + CO2 + H2O.Select ammonium carbonate as the reagent. Verification / Alternative check: Process descriptions for gypsum-to-ammonium-sulfate plants detail carbonation and ammoniation steps leading to CaCO3 precipitation and ammonium sulfate crystallization. Why Other Options Are Wrong: A: NH3 alone does not displace sulfate from CaSO4 effectively. C: Nitric acid would form Ca(NO3)2. D: Not applicable because a suitable reagent exists. E: Ammonium chloride would form CaCl2, not the desired product. Common Pitfalls: Forgetting the role of carbonate in precipitating CaCO3, which shifts equilibrium toward ammonium sulfate formation. Final Answer: ammonium carbonate

Question 6

Agronomy – timing of nitrogen application for crop nutrition When is nitrogenous fertilizer primarily required in field crops, based on plant physiology and nutrient uptake patterns? (Select the most appropriate stage and purpose.)

Accepted Answer

Introduction / Context: Nitrogen is the key macronutrient driving vegetative growth in most crops. The agronomic question is about the correct timing and purpose of nitrogenous fertilizer so that plants develop strong stems and ample leaf area, which later supports flowering and yield. Given Data / Assumptions: Crops exhibit distinct growth stages: establishment, vegetative, reproductive, and maturation. Nitrogen chiefly promotes leaf and stem (shoot) biomass and chlorophyll formation. Over-application late in the season can delay maturity or reduce quality. Concept / Approach: Nitrogen fuels cell division, chlorophyll synthesis, and photosynthetic capacity. Supplying it early (basal and early topdress) maximizes leaf area index, which in turn captures more solar energy to build carbohydrates for later reproductive sinks. Many region-specific recommendations split N between planting and early tillering or crown root initiation (for cereals) to match crop demand and minimize loss pathways (volatilization, leaching, denitrification). Step-by-Step Solution: Identify the physiological role of nitrogen: rapid vegetative growth and chlorophyll formation.Match fertilizer timing to crop demand: early stages need higher available N.Recognize that excessive late N can prolong vegetative growth, lodging risk, and delay harvest.Therefore, the best statement is early-stage application to promote stem and leaf development. Verification / Alternative check: Field trials consistently show that adequate early N increases tiller number (in cereals), canopy cover, and photosynthetic rate, ultimately supporting higher grain or fruit yields when balanced with P, K, and S. Why Other Options Are Wrong: Accelerating fruit formation: Too much late N can reduce fruit set and quality. Lessen excessive potash: Potassium issues are corrected by water management and balanced fertilization, not by extra N. None of these: Incorrect because early nitrogen is clearly beneficial. Common Pitfalls: Applying all N at once; splits are preferred. Ignoring soil organic N supply or residual N can lead to waste and environmental loss. Final Answer: during the early stage of growth to promote development of stem and leaves.

Question 7

Industrial nitric acid by the Ostwald process The oxidation of ammonia followed by absorption of nitrogen oxides in water produces commercial nitric acid of approximately what concentration (weight % HNO3)?

Accepted Answer

Introduction / Context: The Ostwald process converts ammonia to nitric acid via catalytic oxidation to NO/NO2 and subsequent absorption in water. A common exam point is the typical product strength obtained directly from absorption without further concentration steps. Given Data / Assumptions: Feed: anhydrous NH3 and air; Pt-Rh catalyst for oxidation. Absorber: countercurrent water contacting NOx to form HNO3. No secondary concentration by dehydration or extractive methods considered. Concept / Approach: Direct absorption yields a nitric acid solution limited by vapor–liquid equilibrium and heat effects, typically around 55–68 wt%. Plants often report about 60–62 wt% HNO3 as the standard “weak acid” strength, which can later be concentrated (e.g., by azeotropic distillation or extractive techniques) to stronger grades if needed. Step-by-Step Solution: Recognize the product of the absorption column is “weak” nitric acid.Industrial practice targets roughly 60 wt% HNO3 at the absorber outlet.Compare options: 60 matches the customary commercial concentration range.Select 60% as the correct answer. Verification / Alternative check: Process design references list weak nitric acid near 60 wt% from absorption, with higher strengths requiring energy-intensive concentration and water removal. Why Other Options Are Wrong: 30%: Too dilute for standard Ostwald absorption performance. 95% or 100%: These are fuming/super-azeotropic or anhydrous strengths not obtained by simple absorption. Common Pitfalls: Confusing “weak acid” from the absorber with “concentrated nitric acid” supplied for nitration; the latter needs additional unit operations. Final Answer: 60

Question 8

Fertilizer manufacturing equipment – purpose of a prilling tower In which fertilizer process flowsheet is a prilling tower used to form solid spherical prills from a molten melt?

Accepted Answer

Introduction / Context: “Prilling” converts a molten stream into near-spherical solid particles by dropping droplets down a tall tower with countercurrent air cooling. Identifying which fertilizer commonly uses prilling helps connect process equipment to product form and handling properties. Given Data / Assumptions: Molten product capable of forming droplets that solidify in air. Desire for uniform particle size for storage, blending, and application. Alternative finishing routes include granulation and pastillation. Concept / Approach: Urea, produced from ammonia and carbon dioxide, exits the synthesis and concentration sections as a melt. This melt is commonly solidified in a prilling tower (or granulator) to form urea prills. Ammonia is liquefied or stored as anhydrous liquid but not prilled. Superphosphate and triple superphosphate are typically granulated or cured, not produced via prilling of a melt. Step-by-Step Solution: Identify products typically handled as molten streams suitable for prilling.Recognize urea melt is routinely converted to prills in a tall tower.Exclude ammonia (gas/liquid) and SSP/TSP (granulated/cured solids).Select “urea.” Verification / Alternative check: Plant layouts and vendor brochures show urea finishing units with prilling towers or fluidized-bed/granulation alternatives. Why Other Options Are Wrong: Ammonia: Stored under pressure; not prilled. Superphosphate and triple superphosphate: Produced by acidulation and granulation, not by prilling a melt. Common Pitfalls: Confusing prilling (falling droplets) with granulation (agglomeration in rotating drums/pans or fluidized beds). Final Answer: urea

Question 9

Wet-process phosphoric acid production chemistry In the wet process, phosphoric acid is produced by reacting phosphate rock with which reagent under controlled conditions?

Accepted Answer

Introduction / Context: Phosphoric acid (H3PO4) is a critical intermediate for phosphate fertilizers. Industrially, the “wet process” digests phosphate rock with sulfuric acid to produce phosphoric acid and calcium sulfate by-products (gypsum or hemihydrate), after which clarifying and concentration steps follow. Given Data / Assumptions: Feed: apatite-rich phosphate rock (typically fluorapatite). Operating conditions: controlled acid strength and temperature. Objective: maximize P2O5 recovery and manageable gypsum crystals. Concept / Approach: Using dilute sulfuric acid promotes conversion of the phosphate mineral to phosphoric acid while precipitating calcium as gypsum with suitable crystal habit for filtration. Too concentrated acid can hinder crystal growth and filtration. Nitric or hydrochloric routes exist for specialty processes (e.g., nitrophosphate), but the classic wet process uses dilute H2SO4. Step-by-Step Solution: Write the representative reaction of fluorapatite with H2SO4 to form H3PO4 and CaSO4·2H2O.Note the importance of acid strength on crystal size and filtration.Select dilute H2SO4 as the correct reagent.Recognize other acids lead to alternative processes/products (e.g., nitrophosphate). Verification / Alternative check: Process descriptions of dihydrate and hemihydrate routes emphasize sulfuric acid digestion at controlled dilution for optimum gypsum handling. Why Other Options Are Wrong: Concentrated H2SO4: Poor filtration, side reactions. Concentrated HNO3 or HCl: Define different, less common pathways for bulk H3PO4 production. Common Pitfalls: Confusing wet-process acid (fertilizer grade) with purified thermal-process acid made by burning elemental phosphorus. Final Answer: dilute H2SO4 (sulfuric acid)

Question 10

Fertilizer chemistry – structural formula of urea Identify the correct structural formula for urea used in nitrogenous fertilizers.

Accepted Answer

Introduction / Context: Urea is the world’s most widely used solid nitrogen fertilizer, valued for its high nitrogen content (~46% N) and handling properties. Recognizing its chemical structure is basic to understanding hydrolysis, volatilization risks, and soil interactions. Given Data / Assumptions: Urea forms via reaction of ammonia with carbon dioxide under high pressure to make ammonium carbamate followed by dehydration. The structure is a carbonyl flanked by two amide groups. No ions are present in the final solid; it is a neutral organic molecule. Concept / Approach: The correct condensed formula is NH2–CO–NH2, indicating a central carbonyl (C=O) with two terminal amine groups. Alternative strings given either misplace atoms, imply different functional groups, or represent unreal species at standard conditions. The correct identification guides understanding of enzymatic hydrolysis by urease to ammonium and bicarbonate in soils. Step-by-Step Solution: Recall urea’s canonical structure: NH2–CO–NH2.Check options for the carbonyl flanked by two NH2 groups.Reject options implying ionic adducts or methylated carbamates.Select NH2.CO.NH2. Verification / Alternative check: Infrared spectra show a strong carbonyl band and N–H stretches consistent with the diamide structure. Why Other Options Are Wrong: NH3CO.CH3 / NH.CO2.NH / NH3.CO2.NH3: Not urea; these imply other species or unstable adducts. Common Pitfalls: Confusing ammonium carbamate (an intermediate) with urea; the former contains ionic NH4+ and HCOO−-like features prior to dehydration. Final Answer: NH2.CO.NH2

Question 11

Reaction of orthophosphoric acid with soda ash (Na2CO3) The reaction of orthophosphoric acid (H3PO4) with soda ash ultimately yields which industrial phosphate product (after appropriate neutralization and dehydration/condensation steps)?

Accepted Answer

Introduction / Context: Soda ash (Na2CO3) neutralizes phosphoric acid to sodium phosphates. Subsequent thermal dehydration/condensation steps can convert orthophosphate salts into condensed phosphates such as sodium tripolyphosphate (STPP), widely used in detergents and some food applications. Given Data / Assumptions: Acid–base neutralization between H3PO4 and Na2CO3. Controlled stoichiometry to reach desired sodium-to-phosphorus ratio. Heating to drive off water and condense orthophosphates to polyphosphates. Concept / Approach: Neutralization yields mono-, di-, or trisodium phosphate depending on Na2CO3/H3PO4 ratio. Calcination dehydrates and polymerizes these to condensed phosphates. For STPP (Na5P3O10), appropriate feed blending and thermal treatment are applied. Organic phosphates like tricresyl or tributyl phosphate require esterification of phosphorus oxychloride or phosphoric acid with alcohols/phenols, not simple soda ash neutralization. Nitrophosphate is made via nitric acid digestion of rock phosphate, not via Na2CO3 neutralization. Step-by-Step Solution: Neutralize H3PO4 with Na2CO3 to produce sodium phosphate salts.Adjust Na:P ratio to target STPP composition.Calcine/dehydrate to condense orthophosphate to tripolyphosphate.Exclude organic phosphate esters and nitrophosphate routes.Select STPP. Verification / Alternative check: Process descriptions for STPP list feedstocks as H3PO4 plus Na2CO3/NaOH/NaHCO3, followed by spray drying and calcination to form Na5P3O10. Why Other Options Are Wrong: Tricresyl/tributyl phosphate: Organic esters, not formed by soda ash neutralization. Nitrophosphate: Produced via nitric acid route from rock phosphate. Common Pitfalls: Assuming any phosphate product can result from simple neutralization; condensed phosphates require subsequent thermal steps. Final Answer: sodium tripolyphosphate (STPP)

Question 12

Manufacture of sodium tripolyphosphate (STPP) STPP is commercially manufactured by neutralizing phosphoric acid with which sodium base (before dehydration/condensation to the polyphosphate)?

Accepted Answer

Introduction / Context: Sodium tripolyphosphate (Na5P3O10) is a major detergent builder. The first step in its production is forming sodium orthophosphates by neutralizing phosphoric acid with an alkali source before calcination to the tripoly form. Given Data / Assumptions: Feed acid: H3PO4. Candidate sodium bases: carbonate, bicarbonate, phosphate, silicate. Subsequent thermal dehydration/condensation produces STPP. Concept / Approach: Industrial routes use Na2CO3 (soda ash), NaHCO3, and/or NaOH to neutralize H3PO4 to mixed sodium phosphates, then spray-dry and calcine to Na5P3O10. Among the listed bases, sodium carbonate is the standard raw material. Sodium phosphate would be a product, not a base reagent; silicate is not used for neutralizing to STPP; bicarbonate is possible but less typical alone compared to Na2CO3. Step-by-Step Solution: Select a strong sodium base commonly used in bulk chemicals: Na2CO3.Neutralize H3PO4 to sodium orthophosphates.Calcine to form STPP.Therefore, “carbonate” is correct. Verification / Alternative check: Process descriptions and PFDs cite soda ash (and sometimes NaOH) as the neutralizing agent for STPP manufacture. Why Other Options Are Wrong: Phosphate: It is the product class, not the base used for neutralization. Bicarbonate: Usable but not the principal industrial choice in the context given. Silicate: Not relevant to STPP synthesis. Common Pitfalls: Confusing feed reagents with intermediate or final products in phosphate chemistry. Final Answer: carbonate

Question 13

Formulation knowledge – composition of a base suspension fertilizer A “base suspension fertilizer” formulation is commonly designed to contain which approximate analysis (by percent of plant nutrients)?

Accepted Answer

Introduction / Context: Suspension fertilizers are fluid products stabilized with fine solids or clay to hold high nutrient concentrations. “Base suspension” refers to a high-analysis N–P fluid, often used as a stock to which potassium solutions or micronutrients can be added for field-specific blends. Given Data / Assumptions: Common analyses include high P2O5 from superphosphoric acid with moderate N from ammonia. Notation uses oxide forms (P2O5, K2O) as is standard in fertilizer trade. The question seeks the typical iconic base analysis. Concept / Approach: Base suspensions historically align with analyses around 13-43-0 (N–P2O5–K2O), produced by neutralizing superphosphoric acid with anhydrous ammonia in the presence of suspension agents. The high P content improves logistics by reducing water and trucked volume. Other analyses presented either invert the N–P balance unrealistically or list extreme K2O contents inconsistent with base N–P suspensions. Step-by-Step Solution: Identify the common industry shorthand for base suspensions: approximately 13-43-0.Map this to percentage nutrients: 13% N and 43% P2O5.Exclude options with 43% N or high K2O that do not match base N–P products.Select 13% N2 and 43% P2O5. Verification / Alternative check: Ag retail references list base suspensions near 11-37-0 to 13-43-0; farmers then blend K sources (e.g., KCl solution) if required. Why Other Options Are Wrong: 43% N: Uncharacteristically high for fluid suspensions; viscosity and safety issues. Options with K2O: A base N–P suspension typically has no K2O until blended. Common Pitfalls: Confusing suspension fertilizers (which may be opaque and thick) with clear solution fertilizers; suspensions allow higher nutrient loading. Final Answer: 13% N2 and 43% P2O5

Question 14

Nomenclature of phosphoric acids – identify H3PO4 H3PO4 corresponds to which commonly named phosphoric acid type in inorganic chemistry?

Accepted Answer

Introduction / Context: Phosphorus oxyacids appear in several forms. Recognizing their empirical formulas and conventional names is important for fertilizer chemistry, water treatment, and analytical reagents. Given Data / Assumptions: Orthophosphoric acid: H3PO4, the simplest triprotic acid of phosphorus. Pyrophosphoric acid: H4P2O7, a condensed dimer. Metaphosphoric acids: general formula (HPO3)n, polymeric rings or chains. Concept / Approach: H3PO4 is the monomeric, fully hydrated form known as orthophosphoric acid. Condensation of two orthophosphoric molecules removes water to form pyrophosphoric acid. Further condensation produces metaphosphoric (polymeric) forms. Therefore, H3PO4 must be orthophosphoric acid in standard nomenclature. Step-by-Step Solution: Compare formula H3PO4 with known phosphorus oxyacids.Assign the conventional name “orthophosphoric acid”.Exclude pyrophosphoric (dimer) and metaphosphoric (polymer).Confirm selection. Verification / Alternative check: Chemical handbooks universally list H3PO4 as orthophosphoric acid, used widely in fertilizers and food-grade acids. Why Other Options Are Wrong: Pyro: H4P2O7, not H3PO4. Meta: (HPO3)n, different stoichiometry. None: Incorrect because a correct match exists. Common Pitfalls: Mixing up the “ortho,” “pyro,” and “meta” prefixes; remember that condensation increases P:O ratio complexity and changes hydrogen count. Final Answer: orthophosphoric acid

Question 15

Product formed by phosphoric acid treatment of rock phosphate The action of phosphoric acid on rock phosphate (apatite) yields which fertilizer product under standard industrial practice?

Accepted Answer

Introduction / Context: Phosphate fertilizers are made by “acidulating” phosphate rock. The acid used determines the product: sulfuric acid leads to single superphosphate (SSP), whereas phosphoric acid produces triple superphosphate (TSP). Understanding these routes is core to fertilizer process engineering and agronomy. Given Data / Assumptions: Feed mineral: apatite-rich rock phosphate. Acid choices include H2SO4 and H3PO4 for common industrial routes. Objective: produce a plant-available phosphate product with desired P2O5 content. Concept / Approach: When rock phosphate is treated with phosphoric acid, the reaction forms monocalcium phosphate with higher P2O5 analysis and fewer impurities than SSP. This product is called triple superphosphate (typically around 44–48% P2O5). In contrast, sulfuric acid yields single superphosphate (~16–20% P2O5). Nitrophosphate comes from nitric acid digestion; DAP requires neutralizing phosphoric acid with ammonia, not direct rock acidulation. Step-by-Step Solution: Identify the acid: H3PO4 → triple superphosphate pathway.Recall that H2SO4 → single superphosphate.Exclude nitric acid (nitrophosphate) and ammonia neutralization products (DAP).Select triple superphosphate. Verification / Alternative check: Process flowsheets in fertilizer texts show rock + H3PO4 → TSP granulation and curing, with higher P analysis than SSP. Why Other Options Are Wrong: SSP: Produced using sulfuric acid, not phosphoric acid. Nitrophosphate: Requires nitric acid route. DAP: Formed by ammonia neutralization of phosphoric acid, not direct rock treatment. Common Pitfalls: Confusing SSP vs TSP based solely on granule appearance; the key difference is the acid used and resultant P2O5 content. Final Answer: triple superphosphate (TSP)

Question 16

In industrial inorganic chemistry and allotropy of phosphorus: How can red phosphorus be converted back into the more reactive white (yellow) phosphorus during processing? Select the method that achieves this allotropic transformation safely under c…

Accepted Answer

Introduction: Phosphorus exists in several allotropes with distinct structures and reactivities. White (yellow) phosphorus is highly reactive and waxy, while red phosphorus is polymeric and comparatively stable. Understanding how to interconvert these forms is essential in match manufacture, pyrotechnics, and phosphorus handling safety. Given Data / Assumptions: We start with red phosphorus (polymeric, less reactive). Goal: obtain white phosphorus (molecular P4, more reactive). Industrial methods must avoid oxidation and uncontrolled combustion. Concept / Approach: Red phosphorus can revert to white phosphorus by thermal treatment that breaks the polymeric network into discrete P4 molecules. Because white phosphorus forms as a molecular vapor, the practical route is to volatilize phosphorus and then condense the vapor under inert or reducing conditions and without oxygen. This distillation-like approach separates the allotropes based on phase behavior. Step-by-Step Solution: Heat red phosphorus in an oxygen-free environment to generate phosphorus vapor (predominantly P4).Prevent exposure to air to avoid oxidation and ignition.Condense the vapor in water or an inert medium to collect white phosphorus as a solid.Therefore, the correct transformation method is vaporisation followed by condensation. Verification / Alternative check: Reference processing notes show that white phosphorus is commonly stored under water to avoid oxidation; its formation via vapor condensation is a standard route from red phosphorus when required. Why Other Options Are Wrong: Heating in presence of light: Risks photochemical oxidation/ignition; not the controlled conversion route. Melting under pressure: Does not directly produce white phosphorus from red; melting conditions are unsafe and inappropriate. Oxidation in dry air: Produces oxides, not a different allotrope. None of these: Incorrect because vaporisation followed by condensation is valid. Common Pitfalls: Confusing oxidation (a chemical change) with allotropy (a structural change). The transformation requires oxygen exclusion and careful temperature control to avoid combustion. Final Answer: vaporisation followed by condensation.

Question 17

Fuels and by-product gases (coke oven gas): Approximately what percentage by volume of hydrogen is present in typical coke oven gas leaving the recovery system?

Accepted Answer

Introduction: Coke oven gas (COG) is a valuable by-product from the carbonization of coal in metallurgical coke ovens. It contains hydrogen, methane, carbon monoxide, carbon dioxide, nitrogen, and light hydrocarbons. Knowing the hydrogen content is important for calorific value estimation, gas cleaning design, and as a feed for synthesis operations. Given Data / Assumptions: Typical, cleaned coke oven gas composition after tar and ammonia removal. Percentages are approximate volumetric percentages. Plant-to-plant variability exists, but standard textbook values are acceptable. Concept / Approach: Standard compositions show hydrogen as the major component of COG. Typical ranges are roughly: H2 (50–60%), CH4 (25–30%), CO (5–10%), CO2 (1–3%), N2 and others (balance). Selecting a representative value within the standard range ensures accurate preliminary design calculations and energy balances. Step-by-Step Solution: Identify the dominant constituent of COG: hydrogen.Recall the common textbook value: about 55–60% by volume.Choose the nearest offered value in the list: 58%. Verification / Alternative check: Plant data sheets for coke ovens and fuel system references typically quote hydrogen near 55–60% vol., validating the selection of 58% as a representative value. Why Other Options Are Wrong: 4% or 22%: Far below typical hydrogen content; would imply an atypical gas. 84%: Too high; not consistent with the presence of methane and carbon oxides. 35%: Still well below the usual range. Common Pitfalls: Confusing COG with blast furnace gas (which is CO/CO2 rich and much lower in H2) or with producer gas. Each process gas has a distinct signature composition and calorific value. Final Answer: 58

Question 18

Indian fertilizer industry (gas-based plants): Among the following pairs, identify the states that host two well-known gas-based fertilizer plants (using natural gas/NG as feed-stock).

Accepted Answer

Introduction: Gas-based fertilizer plants produce ammonia and urea using natural gas as the primary feed and fuel, leveraging the high hydrogen content and clean combustion. In India, plant siting correlates with gas availability and pipeline connectivity. This question checks recognition of major gas-based clusters by state. Given Data / Assumptions: Focus on states, not specific plant names. Historical and present-day siting favors western/central gas corridors. Pairs provided include plausible but incorrect combinations. Concept / Approach: Gujarat has significant petrochemical and fertilizer capacity associated with gas terminals and networks (e.g., Hazira). Madhya Pradesh hosts large gas-based units (e.g., at Vijaipur), supplied via national gas pipelines. The pair Gujarat–Madhya Pradesh is a classic textbook answer to “two gas-based fertilizer plants are located in …”. Step-by-Step Solution: Identify gas-rich/connected states: Gujarat and Madhya Pradesh.Exclude pairs that include coal-centric or less gas-linked states for such plants.Select “Gujarat and Madhya Pradesh”. Verification / Alternative check: Industry directories and historical overviews repeatedly cite Hazira (Gujarat) and Vijaipur (Madhya Pradesh) as archetypal gas-based ammonia-urea centers. Why Other Options Are Wrong: Maharashtra and Gujarat: While both have relevant industry, the canonical pair in standard questions is Gujarat–Madhya Pradesh. Maharashtra and Orissa; Jharkhand and Chhattisgarh; Tamil Nadu and Rajasthan: These pairs do not represent the classic duo of gas-based hubs referenced in traditional exam keys. Common Pitfalls: Mixing coastal refinery locations with gas-based fertilizer siting; the decisive factor is gas feedstock, not merely industrial activity. Final Answer: Gujarat and Madhya Pradesh

Question 19

Urea manufacturing chemistry (biuret control): In molten urea processing, what is the effect of operating at a lower temperature with a large excess of ammonia on biuret formation?

Accepted Answer

Introduction: Biuret is a by-product formed when two urea molecules condense, releasing ammonia. Excessive biuret in urea fertilizer is undesirable because it can harm sensitive crops, especially at seedling stages. Process conditions strongly influence the extent of biuret formation. Given Data / Assumptions: Molten urea stage where side reactions can occur. Variables: temperature and ammonia (NH3) excess. Goal: minimize biuret content in the product. Concept / Approach: Biuret forms via thermal condensation: 2 urea → biuret + NH3. The reaction is favored at higher temperatures and when free ammonia is scarce. Operating at lower temperatures suppresses the endothermic condensation. A high NH3 partial pressure shifts equilibria to favor urea and discourage further condensation to biuret and higher condensates (e.g., triuret, cyanuric species). Step-by-Step Solution: Reduce temperature of the urea melt to slow thermal condensation kinetics.Maintain a large excess of ammonia to shift the reaction away from biuret formation.Result: biuret concentration decreases in the final urea product. Verification / Alternative check: Plant guidelines specify temperature control and NH3 excess in the synthesis/finishing sections to keep biuret within specification (often below ~1% for prilled/granular product depending on grade). Why Other Options Are Wrong: Increases or no effect: Opposite to established kinetics and equilibrium. “Is undesirable”: Condition itself is actually desirable for minimizing biuret. Cyanuric acid comment: Not the primary controlled pathway in this context. Common Pitfalls: Allowing hot holdup and long residence times; both raise biuret. Also, insufficient NH3 recycle can worsen condensation products. Final Answer: decreases biuret formation

Question 20

Fertilizer classification: Urea is classified as which type of plant nutrient fertilizer based on its primary nutrient content?

Accepted Answer

Introduction: Fertilizers are categorized by the primary nutrient supplied: nitrogen (N), phosphorus (P), or potassium (K). Urea is one of the most widely used fertilizers globally due to its high nitrogen content and favorable handling characteristics. Given Data / Assumptions: Urea chemical formula: CO(NH2)2. Typical nutrient analysis: 46% N by weight. Application: broadacre crops, horticulture, and blended products. Concept / Approach: Because urea contains only nitrogen as a primary nutrient (no P2O5 or K2O), it is categorized as a nitrogenous fertilizer. It can be used alone or as a component of compound blends, but its classification depends on its inherent nutrient makeup, not the blend it may be added to. Step-by-Step Solution: Identify nutrient content: high nitrogen, negligible phosphorus or potassium.Match with fertilizer category: nitrogenous.Confirm: Urea’s analysis (46-0-0) in N-P2O5-K2O terms supports the classification. Verification / Alternative check: Standard fertilizer labeling and agronomy texts list urea as a straight nitrogen fertilizer with the highest N content among common granular sources. Why Other Options Are Wrong: Potassic or phosphatic: Urea contains neither K nor P as primary nutrients. Mixed NPK: While urea can be part of blends, the pure product is not a mixed NPK fertilizer. None of these: Incorrect because nitrogenous is correct. Common Pitfalls: Confusing fertilizer classification with application method; coating or stabilizers do not alter the primary nutrient category. Final Answer: nitrogenous

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