৪৯তম বিসিএস ⎯ ফলিত রসায়ন [৫৪১]

In the Kraft pulping process:
1.Wood chips are cooked in a strong alkaline solution called white liquor, which mainly contains:
    1.Sodium hydroxide (NaOH)
    2.Sodium sulfide (Na₂S)
2.These chemicals break down the lignin structure, cleaving ether and carbon–carbon bonds, and dissolve lignin from the cellulose fibers.
3.The process effectively separates cellulose (for paper) from lignin and hemicellulose.

Other options:
ক) Sodium sulfate – Not used for lignin dissolution; it’s present in the recovery cycle.
খ) Calcium bisulfite – Used in sulfite pulping, not Kraft.
ঘ) Sodium carbonate – Minor role in the recovery loop, not primary for lignin removal.

The major difference between the Sulfite and Kraft processes that affects paper properties is:
Kraft process:
    1.Uses strong alkaline conditions (NaOH + Na₂S).
    2.Effectively removes lignin, leaving long, intact cellulose fibers.
    3.Produces stronger, more durable paper, suitable for packaging and industrial applications.
Sulfite process:
    1.Uses acidic or weakly acidic conditions with bisulfite salts.
    2.Can lead to shorter fibers and partial degradation of cellulose.
    3.Produces softer, less strong paper, often used for fine printing papers.

Other options:
ক) Sulfite produces stronger pulp – Incorrect; Kraft pulp is stronger.
গ) Kraft retains more lignin – Opposite is true; Kraft removes more lignin.
ঘ) Sulfite operates at higher alkalinity – Sulfite is generally acidic; Kraft is strongly alkaline.

In the viscose process for rayon production:
   1.Cellulose from wood or cotton linters is treated with sodium hydroxide to form alkali cellulose.
   2.Carbon disulfide (CS₂) reacts with alkali cellulose to produce cellulose xanthate, which is soluble in dilute NaOH.
   3.This viscous solution (viscose) can then be extruded through spinnerets and regenerated into cellulose fibers in an acidic coagulation bath.

Other options:
ক) Preventing coagulation during fiber extrusion – Not the role of CS₂; this is controlled by the spinning bath chemistry.
খ) Neutralizing caustic soda – CS₂ does not neutralize NaOH.
ঘ) Regenerating cellulose fibers – Regeneration is done in the acidic coagulation bath, not by CS₂.

Kraft pulp mills are known for producing “kraft odor” due to:

Reduced sulfur compounds, such as:
   1.Hydrogen sulfide (H₂S)
   2.Methyl mercaptan (CH₃SH)
   3.Dimethyl sulfide (CH₃)₂S
These compounds are volatile, malodorous, and toxic, leading to air pollution and community complaints.

Other Options:
ক) SO₂ release – Major concern in sulfite pulping, not Kraft.
খ) Lignosulfonates in effluent – Specific to sulfite process, not Kraft.
ঘ) Calcium salts discharge – Associated with lime recovery in sulfite or other processes, not the main Kraft environmental issue.

In a Kraft pulping plant, the recovery boiler plays a critical role:
    1.Burns organic matter in black liquor (mainly lignin and other organics) to generate heat.
    2.This heat is used to produce steam, which can drive turbines or provide process heat.
    3.Inorganic pulping chemicals (mainly sodium carbonate and sodium sulfide) are recovered as smelt, which is later converted back into white liquor for reuse in pulping.

Other options:
ক) Burn lignin and regenerate sodium sulfate from sodium sulfide – Sodium sulfate regeneration occurs in the lime kiln and recausticizing plant, not directly in the recovery boiler.
গ) Neutralize black liquor – Black liquor is concentrated and burned; neutralization occurs later if needed.
ঘ) Remove dioxins – Not a primary function; dioxin control is part of effluent/air treatment.

CS₂ emissions are a major environmental concern in the viscose process for rayon production, because carbon disulfide is toxic, volatile, and polluting.
The N-methylmorpholine N-oxide (NMMO) lyocell process:
    1.Dissolves cellulose directly without forming cellulose xanthate.
    2.Eliminates the use of carbon disulfide (CS₂) entirely.
    3.Produces environmentally friendly fibers with high quality.

Other options:
ক) Cuprammonium process – Uses copper-ammonia complex; reduces CS₂, but less industrially preferred due to heavy metal concerns.
গ) Increasing NaOH concentration – Does not significantly reduce CS₂ emissions; it affects alkali cellulose formation.
ঘ) Chlorine dioxide bleaching – Reduces chlorine-related pollution, not CS₂ emissions.

In the Kraft pulping process:  1.Sodium hydroxide (NaOH) provides strong alkalinity, helping to swell wood chips and partially cleave lignin bonds.
2.Sodium sulfide (Na₂S) acts as a nucleophile, specifically targeting aryl-ether bonds in lignin.
3.The combination of NaOH and Na₂S efficiently dissolves lignin, separating it from cellulose fibers for pulp production.

Other options:
ক) Bleaching agent – Na₂S is not a bleaching chemical; bleaching occurs after pulping.
খ) Prevent cellulose degradation – The main role is lignin removal, not cellulose protection.
গ) Reduce silica scaling – Scaling is controlled by other methods, not by Na₂S.

In soap production by saponification:
1.Saturated fatty acids (like stearic and palmitic acid) produce hard, firm soap.
2.Unsaturated fatty acids (like oleic and linoleic acid) produce softer, more pliable soap.
3.Therefore, the hardness of the final soap is primarily determined by the composition of the fat/oil feedstock, specifically the saturated-to-unsaturated ratio.

Other options:
ক) Alkali concentration – Influences reaction completeness, but not directly the final soap hardness.
খ) Glycerol content – Affects moisturizing properties, not hardness.
ঘ) Salting-out temperature – Affects soap separation efficiency, not intrinsic hardness.

Linear alkylbenzene sulfonates (LAS) are synthetic anionic surfactants with the general structure R–C₆H₄–SO₃⁻Na⁺, where R is a linear alkyl chain.
Key advantage over soap:
    1.The sulfonate (-SO₃⁻) group is highly water-soluble and does not form insoluble precipitates with hard water ions like Ca²⁺ or Mg²⁺.
    2.In contrast, soap (R–COO⁻Na⁺) forms scum in hard water due to precipitation with Ca²⁺/Mg²⁺.

Other options:
খ) Absence of hydrophobic tail – Incorrect; LAS has a long hydrophobic alkyl chain.
গ) Ability to form micelles without CMC – Micelle formation still requires critical micelle concentration.
ঘ) Stronger hydrogen bonding – Surfactant action is dominated by hydrophobic/hydrophilic balance, not H-bonding.

During soap manufacturing, glycerine is produced as a by-product in the saponification reaction.
1.Sweet water contains dissolved glycerine along with salts and residual soap.
2.Vacuum evaporation is preferred because:
     1.It lowers the boiling point of water.
     2.This prevents high-temperature decomposition of glycerine, which is thermally sensitive.
     3.Ensures high-purity glycerine recovery.

Other options:
ক) Simultaneous neutralization – Not a function of vacuum evaporation.
খ) Increases saponification rate – Reaction is already complete; evaporation only separates glycerine.
ঘ) Converts glycerine into aldehyde – Undesired reaction; not intended in soap industry.

In powder detergent manufacturing, bulk density is primarily controlled during the spray-drying step:
   1.The liquid slurry of detergent ingredients is sprayed into a hot air tower.
   2.Droplet size, drying rate, and tower conditions determine the particle size and porosity of the detergent granules.
   3.Larger, less porous particles → higher bulk density.
   4.Smaller, more porous particles → lower bulk density.

Other options:
​খ) Neutralization – Controls pH and active content, not bulk density.
গ) Addition of optical brighteners and perfumes – Affects aesthetics and performance, not bulk density.
ঘ) Anti-redeposition agents – Enhance cleaning efficiency, not particle density.

In Kraft pulping, sulfidity is defined as the ratio of Na₂S to total alkali (NaOH + Na₂S) in the white liquor.
High sulfidity (>30%) increases the concentration of sodium sulfide (Na₂S).
This leads to:
    1,Higher emission of reduced sulfur compounds (TRS) such as H₂S, CH₃SH, and dimethyl sulfide.
    2.Foul odor, environmental complaints, and corrosion in equipment.

Other options:
ক) Excessive cellulose degradation – High alkalinity, not high sulfidity, primarily causes cellulose damage.
গ) Low-calorific black liquor – Depends on solids content, not sulfidity.
ঘ) Calcium carbonate deposition – Related to water hardness, not sulfidity.

In chrome tanning:
Basic chromium sulfate (Cr₂(SO₄)₃·xH₂O) is the primary tanning agent.
It penetrates collagen fibers and forms ionic and coordinate crosslinks with the carboxyl groups of collagen.
These crosslinks stabilize the protein structure, making the leather:
   1.Heat-resistant
   2.Water-resistant
   3.Durable and flexible

Other options:
ক) Only a dyeing agent – Incorrect; Cr³⁺ is a crosslinker, not a colorant.
খ) Removes non-collagenous proteins – That is part of liming and bating, not tanning.
গ) Acts as softening agent only – Softening is a separate post-tanning step; chrome’s main role is stabilization.

In vegetable tanning:
Pre-treatment steps like liming and deliming are crucial:
    1.Liming: Uses calcium hydroxide (Ca(OH)₂) to remove hair, epidermis, and some non-collagenous proteins, and swells the fibers, opening up the structure.
    ​2.Deliming: Neutralizes excess alkali and prepares the pH for tannin penetration.
These steps ensure uniform and deep penetration of tannins into the collagen matrix.

Other options:
ক) Increase water content – Swelling occurs, but the main goal is removal of unwanted components.
গ) Introduce polyphenolic compounds – This happens during actual vegetable tanning, not pre-treatment.
ঘ) Neutralize the pH of tannins – Deliming adjusts pH of hide, not tannins themselves.

In chrome tanning, the penetration of Cr³⁺ ions into collagen fibers is highly sensitive to:

pH of the tanning solution:
    1.Low pH (<3) slows penetration because Cr³⁺ ions are more reactive and tend to precipitate.
    2.Optimal penetration occurs around pH 3–4.5, where chromium forms stable, soluble basic chromium sulfate complexes.
Chromium(III) complex stability:
    1.Stable complexes ensure a controlled reaction rate with collagen, allowing uniform penetration.
​
Other Options:
ক) Atmospheric pressure – Has minimal impact; chromium diffusion is driven by concentration gradient and complex stability.
খ) Drum rotation type – Affects mechanical mixing, but penetration depends more on chemical conditions.
ঘ) Hide thickness and temperature – Influence rate, but pH and Cr³⁺ chemistry dominate.

Vegetable-tanned leather vs chrome-tanned leather:
Vegetable tanning uses polyphenolic tannins from plant sources.
    1.Forms hydrogen bonds and some covalent interactions with collagen.
    2.Results in strong, firm leather with good tensile strength.
    3.Shrinkage temperature is lower (~70–80 °C) than chrome-tanned leather (~100–120 °C), so thermal stability is less.
Chrome tanning:
Forms ionic and coordinate crosslinks with Cr³⁺, giving higher shrinkage temperature, faster processing, and better heat/water resistance.

Other options:
খ) Higher thermal stability and faster processing – True for chrome tanning, not vegetable tanning.
গ) Softer feel and greater water resistance – Chrome-tanned leather tends to be softer and more water-resistant.
ঘ) Lighter color and reduced environmental impact – Color varies; environmental impact depends on process management.

In chrome tanning, monitoring chromium exhaustion is critical to ensure:
Proper penetration of Cr³⁺ into the collagen fibers.
Avoiding under- or over-tanning, which affects leather quality.
Back-titration method:
    1.Measures both free Cr³⁺ ions in the tanning bath and chromium fixed in the leather.
    2.Provides an accurate quantitative assessment of chromium uptake and exhaustion efficiency.

Other options:
ক) Leather thickness – Not related to chromium content.
খ) Visual color change – Subjective and unreliable.
ঘ) pH changes – pH is important for tanning conditions but does not directly indicate chromium exhaustion.

Chrome tanning uses trivalent chromium (Cr³⁺), which is relatively safe and effective for tanning. However:
1.During effluent treatment, oxidation, or improper disposal, some Cr³⁺ can oxidize to Cr⁶⁺.
2.Hexavalent chromium (Cr⁶⁺) is highly toxic, carcinogenic, and environmentally persistent, posing serious risks to soil, water, and human health.

Other options:
ক) High BOD – More typical of vegetable tanning effluents due to organic tannins.
গ) Excessive water consumption – A process concern, not a chemical toxicity issue.
ঘ) SO₂ release – Not a major issue in chromium tanning; sulfur compounds are more relevant in sulfide treatments.

In solvent extraction of edible oils (e.g., using hexane):
Solvent polarity:
    1.Hexane is nonpolar, which makes it highly effective for dissolving nonpolar triglycerides from oilseeds.
    2.Solvent choice affects solubility and extraction efficiency.
Seed particle size:
    1.Smaller particle size increases surface area, allowing better contact between solvent and oil, improving yield.

Other Options:
খ) Boiling point of the solvent – Relevant for solvent recovery, not oil yield directly.
গ) Seed moisture content – Excess moisture can hinder extraction, but it’s secondary to particle size and solvent polarity.
ঘ) Ambient temperature – Minor effect; extraction is usually done under controlled temperatures.

In degumming of crude vegetable oils:
Phospholipids (gums) are naturally present in crude oils.
They can cause:
    1.Emulsion formation during refining, hindering oil-water separation.
    2.Foaming, poor filtration, and reduced oxidative stability.
Degumming (using water, acid, or enzymatic treatment) hydrates and removes phospholipids, producing oil that is:
    1.Clearer
    2.More stable
    3.Easier to refine further

Other options:
ক) Free fatty acids – Removed during neutralization (alkali refining), not degumming.
গ) Proteins – Not a significant impurity in oils; may be part of gums.
ঘ) Waxes – Removed during dewaxing or winterization, not degumming.

In hydrogenation of vegetable oils:
Nickel (Ni) catalyst facilitates the addition of hydrogen (H₂) across the double bonds of unsaturated fatty acids.
This process converts unsaturated fats (liquid at room temperature) into more saturated fats (solid or semi-solid), improving:
    1.Oxidative stability
    2.Shelf life
    3.Spreadability (for products like margarine)

Other options:
খ) Remove phospholipids – Done during degumming, not hydrogenation.
গ) Increase free fatty acids – Free fatty acids are usually removed, not increased.
ঘ) Bleach the oil – Achieved during bleaching with clay, not hydrogenation.

Iodine value (IV) measures the amount of iodine (in grams) that reacts with 100 g of oil or fat.
Double bonds in unsaturated fatty acids react with iodine; thus:
    1.Higher IV → more unsaturated fatty acids → more double bonds
    2.Lower IV → more saturated fatty acids → fewer double bonds
It is an important parameter to assess:
    1.Oxidative stability
    2.Suitability for hydrogenation
    3.Nutritional and industrial applications

Other options:
খ) Moisture content – Affects processing but not iodine value.
গ) Free fatty acids – Measured by acid value, not IV.
ঘ) Phospholipids – Removed during degumming; do not directly affect IV.

Hydrolytic rancidity occurs when triglycerides are broken down by water and lipase enzymes, producing free fatty acids (FFA).
Acid value (AV) measures the amount of KOH (mg) required to neutralize the free fatty acids in 1 g of oil.
      Higher acid value → more free fatty acids → greater hydrolytic rancidity.

Other options:
ক) Iodine value – Measures unsaturation; not rancidity.
খ) Saponification value – Indicates average molecular weight of triglycerides.
ঘ) Peroxide value – Detects oxidative rancidity, not hydrolytic.

Winterization (also called dewaxing) is a physical refining process for liquid oils like sunflower, corn, or soybean oil.
It involves:
    1.Cooling the oil to precipitate high-melting-point triglycerides or waxes.
    2.Filtration to remove the precipitates.
Purpose:
    1.Prevents cloudiness or frosting when oils are stored at low temperatures.
    2.Ensures clear, visually appealing oil.

Other options:
ক) Increase iodine value – Winterization does not affect the degree of unsaturation.
গ) Remove free fatty acids – Done during neutralization, not winterization.
ঘ) Convert unsaturated fats to saturated fats – Occurs during hydrogenation, not winterization.

In paints and coatings, pigments are solid particles that serve several key functions:
  1.Color – Provide the desired hue to the paint.
  2.Opacity / hiding power – Cover the underlying substrate.
  3.Protection – Certain pigments, like titanium dioxide, shield the surface from UV light and environmental degradation.

Other options:
ক) Control drying rate – Mainly determined by solvents and binders, not pigments.
খ) Main film-forming component – This is the binder/resin, not the pigment.
গ) Act as solvents – Pigments are solid particles, not solvents; they do not reduce viscosity.

In alkyd resin-based paints:
Alkyd resins are made by polycondensation of polyhydric alcohols, polybasic acids, and oils (natural or synthetic).
Oil-to-alcohol ratio determines:
     1.Degree of crosslinking
     2.Flexibility and hardness
     3.Gloss and durability of the cured coating
Higher oil content → more flexible and glossy coatings.
Lower oil content → more rigid and less glossy, but potentially more brittle.

Other options:
গ) Particle size of pigment – Affects color, opacity, and surface smoothness, but not the intrinsic gloss and durability controlled by resin chemistry.
ঘ) Ambient temperature during pigment grinding – Minor effect; mainly influences pigment dispersion, not resin properties.
খ) Molecular weight of solvent – Solvent affects viscosity and drying, not the cured coating’s intrinsic gloss/durability.

For outdoor wood protection, the varnish must provide:
    1.High UV resistance – To prevent degradation and color fading under sunlight.
    2.Water repellency – To protect against moisture and weathering.
    3.Durability and abrasion resistance – To withstand environmental wear.
Oil-modified polyurethane varnishes:
    1.Are highly durable, chemically resistant, and form a hard, protective film.
    2.Contain UV stabilizers in many formulations for outdoor use.
    3.Provide water and weather resistance, making them ideal for exterior wood surfaces.

Other options:
ক) Water-based acrylic varnish – Good for indoor use; limited UV/water protection outdoors.
খ) Shellac varnish – Poor water and UV resistance; not suitable for outdoor use.
গ) Spirit varnish – Rapid-drying, good gloss, but weak in water and UV resistance.

Extender pigments are inexpensive, inert materials added to paints and coatings to:
   1.Reduce production cost – They partially replace expensive prime pigments.
   2.Modify rheology – Affect flow, leveling, and application properties.
   3.Improve opacity and hiding power – By scattering light, though less effectively than titanium dioxide.
   4.Maintain color neutrality – They do not impart significant color.
Examples include: kaolin, calcium carbonate, silica, talc.

Other options:
ক) Provide gloss and color – That’s the role of prime pigments, not extenders.
গ) Increase drying time and reduce adhesion – Not the primary purpose.
ঘ) Enhance chemical resistance only – Some extenders may improve chemical resistance marginally, but it is not their main function.

Lacquers vs. Varnishes:
Lacquers:
 1.Use fast-evaporating organic solvents (e.g., nitrocellulose in alcohol or acetone).
 2.Dry rapidly by solvent evaporation, forming a hard, glossy film.
 3.Typically air-dried; no chemical curing needed.
Varnishes:
 1.Usually oil- or resin-based.
 2.Dry slowly by oxidation or polymerization.
 3.Produce a more flexible film but take longer to harden.
​
Other options:
ক) High solid content and slow drying – True for varnishes, not lacquers.
খ) Requiring heat curing – Not typical for standard lacquers.
ঘ) Water-based and non-flammable – Refers to modern waterborne coatings, not traditional lacquers.

In titanium dioxide (TiO₂) pigment production for paints:
TiO₂ is highly effective as a white pigment, providing opacity and brightness.
However, uncoated TiO₂ is photocatalytically active, which can degrade organic binders in coatings when exposed to UV light.
Surface coating with inert oxides like alumina (Al₂O₃) or silica (SiO₂):
  1.Reduces photocatalytic activity.
  2.Improves dispersibility in the paint medium.
  3.Enhances stability and longevity of the coating.

Other options:
গ) Substituting Ti with Zn – Not standard; would change pigment properties.
ঘ) Adding metallic impurities – Increases opacity minimally; does not control photocatalysis.
খ) Increasing particle size – Reduces opacity, which is undesirable.

In the Kraft pulping process, white liquor contains:
     NaOH (sodium hydroxide) – directly reacts with lignin
     Na₂S (sodium sulfide) – contributes to delignification indirectly
Effective alkali (EA) is defined as:
      EA=[NaOH]+0.5×[Na₂S]
This represents the combined delignifying strength of the liquor, used to calculate chemical charge for pulping.

Other options:
ক) Total NaOH present in the white liquor → Only part of the story; ignores contribution of Na₂S.
খ) Total Na₂S present in the white liquor → Only sulfide, does not account for NaOH.
ঘ) Na₂SO₄ content used in recovery → Not part of effective alkali; Na₂SO₄ is a recovery chemical.

In the Kraft pulping process, white liquor contains:
      NaOH (sodium hydroxide) – directly reacts with lignin
      Na₂S (sodium sulfide) – contributes to delignification indirectly
Effective alkali (EA) is defined as:
      EA=[NaOH]+0.5×[Na₂S]
This represents the combined delignifying strength of the liquor, used to calculate chemical charge for pulping.
 
Other options:
ক) Total NaOH present in the white liquor → Only part of the story; ignores contribution of Na₂S.
খ) Total Na₂S present in the white liquor → Only sulfide, does not account for NaOH.
ঘ) Na₂SO₄ content used in recovery → Not part of effective alkali; Na₂SO₄ is a recovery chemical.

1.In the viscose process, cellulose is treated with NaOH to form alkali cellulose.
2.Aging involves controlled depolymerization:Reduces the degree of polymerization (DP) of cellulose
        Improves solubility in carbon disulfide (CS₂) during xanthation
        Ensures a uniform viscose solution suitable for spinning fibers
 
Other options:
ক) Increase molecular weight of cellulose → Opposite effect; aging reduces DP.
খ) Remove hemicellulose from cellulose → Hemicellulose is removed during pulping, not aging.
গ) Stabilize xanthate formation → Xanthate stability depends on CS₂ reaction and temperature, not aging.

1.Chlorine-based bleaching (elemental chlorine or hypochlorite) reacts with residual lignin in pulp.
2.This forms chlorinated organic compounds such as chloroform, chlorophenols, collectively measured as AOX.
3.AOX are:
      Toxic
      Persistent in the environment
      Regulated in pulp mill effluents
 
Other options:
ক) SO₂ emissions → Associated with sulfite pulping, not bleaching.
খ) Formation of lignosulfonates → By-product of sulfite pulping, not chlorine bleaching.
ঘ) TRS gas emissions → Originates from sulfide cooking liquor, not chlorine bleaching.
 

1.Soda-AQ pulping is an improved version of the soda pulping process for non-wood fibers.
2.Anthraquinone (AQ) acts as a redox catalyst:
       Promotes the selective oxidation of lignin and its dissolution into the cooking liquor.
       Protects cellulose and hemicellulose (carbohydrates) from excessive degradation.
       Improves pulp yield and strength.
 
Other options:
খ) Increase lignin solubility → AQ indirectly helps, but the main role is protecting carbohydrates.
গ) Enhance chlorine consumption → Not relevant; AQ is used in soda pulping, which is chlorine-free.
ঘ) Reduce cooking temperature → AQ may allow milder conditions, but this is secondary.
 

1.Soap hardness is largely determined by the saturation and chain length of fatty acids:
        Saturated long-chain fatty acids (like stearic acid, C18:0) produce hard, firm soaps.
       Unsaturated fatty acids (oleic, linoleic) produce soft or liquid soaps.
       Hydroxylated fatty acids (ricinoleic acid from castor oil) produce very soft, moisturizing soaps.
2.Stearic acid is commonly used in combination with palmitic acid to produce hard bar soaps that retain shape and lather well.
 
Other options:
ক) Oleic acid → Makes soft soap; contributes to lather but not hardness.
খ) Linoleic acid → Polyunsaturated; yields soft, easily soluble soap.
ঘ) Ricinoleic acid → Produces soft, emollient soap; lowers hardness.

1.Linear alkylbenzene sulfonates (LAS) are widely used in detergents because:
      Their linear structure is easily attacked by microbes, making them biodegradable.
      They help reduce environmental persistence and pollution in water bodies.
2.Branched alkylbenzene sulfonates (BAS):
      Are less biodegradable due to steric hindrance from branching.
      Were widely used earlier but caused long-term water pollution (foam and organic load).
 
Other options:
ক) Lower foaming → LAS actually produces good foaming.
গ) Higher solubility in water → Both LAS and BAS are water-soluble; solubility is not the main advantage.
ঘ) Less sensitivity to temperature → Not a primary advantage; biodegradability is key.
 

1.In soap-making, glycerine is formed as a by-product.
2.Salting-out involves adding sodium chloride (NaCl) to the soap solution:
      Salt reduces the solubility of glycerine in water (salting-out effect).
      This causes glycerine to separate from the soap solution and form a glycerine-rich aqueous layer, which can be collected.
3.This is a physical separation method, not a chemical reaction.
 
Other options:
খ) Neutralize residual alkali → Neutralization is done separately with acid if needed.
গ) Increase soap hardness → Soap hardness depends on fatty acid composition, not salting-out.
ঘ) Decrease free fatty acids → FFA removal is achieved during saponification or refining, not by adding salt.

1.Saponification value (SV) measures the mg of KOH required to saponify 1 g of fat/oil.
2.High SV indicates:
       More ester bonds per gram of fat
       Which occurs when the average molecular weight of triglycerides is low (short-chain fatty acids).
3.In other words, short-chain triglycerides require more KOH per gram to saponify than long-chain triglycerides.
 
Other options:
ক) High content of free fatty acids → SV is based on esterified fatty acids, not free fatty acids.
খ) High iodine value → IV measures unsaturation, not SV.
গ) High unsaturation in fatty acids → Unsaturation affects IV, not SV directly.
 

1.In modern continuous soap-making, the soap contains moisture after saponification.
2.Vacuum drying is used to:
     Lower the water content efficiently
     Operate at lower temperatures than atmospheric drying
     Prevent thermal decomposition of the soap and preserve quality (color, fragrance, and chemical integrity)
 
Other options:
ক) Increase glycerine content → Glycerine recovery is separate; vacuum drying does not increase glycerine.
গ) Improve soap color → Some color stabilization may occur indirectly, but it’s not the primary purpose.
ঘ) Remove residual alkali → Neutralization is done chemically before drying, not by vacuum drying.
 

1.In chrome tanning, chromium (III) salts can precipitate as Cr(OH)₃ in alkaline pH zones, which reduces tanning efficiency.
2.Masking agents (like sodium salts of amino acids, EDTA, or formates) are added to:
        Complex free chromium ions temporarily
        Prevent premature precipitation in alkaline conditions
        Ensure uniform penetration of chromium into the leather
 
Other options:
ক) Increase the shrinkage temperature of leather → Achieved by proper chromium uptake, not masking agents.
গ) Replace tanning salts → Masking agents do not replace Cr salts; they assist their action.
ঘ) Enhance leather softness → Softness is controlled by post-tanning treatments like fatliquoring.

1.Vegetable tanning uses tannins from plant sources.
     These are organic compounds that dissolve partially into wastewater.
      Resulting effluent has high BOD (biochemical oxygen demand) and color load.
2.Chrome tanning:
      Uses Cr³⁺ salts, which are inorganic and produce lower BOD but require proper Cr disposal to prevent toxicity.
 
Other options:
ক) Vegetable tanning generates Cr⁶⁺ → False; Cr⁶⁺ comes from improper chrome tanning, not vegetable tanning.
খ) Chrome tanning consumes more water but produces stronger leather → True for strength and water usage, but the question asks about environmental impact, not product quality.
ঘ) Chrome tanning uses no salts → False; chromium salts are essential in chrome tanning.

1.Fatliquoring is a post-tanning process in leather finishing.
2.Purpose:
Introduce oils, fats, or emulsions into the leather
Lubricate and separate collagen fibers, improving:
   Softness
   Flexibility
   Elasticity
3.Essential for making wearable, supple leather.
 
Other options:
খ) Removing residual tannins → Done during washing or neutralization, not fatliquoring.
গ) Crosslinking collagen with chromium → Occurs during chrome tanning, not fatliquoring.
ঘ) Adding dyes to leather surface → Done during dyeing or finishing, separate from fatliquoring.
 

1.Pickling is a pre-tanning step in chrome tanning where hides are treated with:
       Sulfuric acid (H₂SO₄)
       Sodium chloride (NaCl)
2.Purpose:
       Lower the pH of the hide to around 2.5–3.0
       Convert collagen amino groups to protonated form, which enhances chromium (III) salt penetration
       Prepares the hide for uniform and effective tanning
 
Other options:
ক) Increase water content in the hide → Hydration occurs earlier during soaking, not pickling.
খ) Remove residual non-collagen proteins → Done during liming and deliming, not pickling.
ঘ) Stabilize collagen fibers thermally → Achieved during tanning, not pickling.

1.Neutralization (or chemical refining) is a step in edible oil refining.
2.Purpose:
Remove free fatty acids (FFA) present in crude oil
Achieved by treating oil with alkali (commonly NaOH) to form soap stock:
R-COOH + NaOH → R-COONa + H₂O
3.This step reduces acidity, improves stability, and prepares oil for further bleaching and deodorization.
 
Other options:
খ) Bleach pigments → Done during the bleaching step, not neutralization.
গ) Remove phospholipids → Achieved by degumming, not neutralization.
ঘ) Hydrogenate unsaturated fatty acids → Performed during hydrogenation, separate from neutralization.

1.Peroxide value (PV) measures the amount of peroxides and hydroperoxides formed in an oil.
2.These compounds are primary oxidation products formed when unsaturated fatty acids react with oxygen.
3.PV is expressed as milliequivalents of active oxygen per kg of oil (meq O₂/kg).
4.It indicates the initial stage of rancidity before formation of secondary products like aldehydes or ketones.
 
Other options:
ক) Free fatty acid content → Measured by acid value, not PV.
খ) Degree of unsaturation → Measured by iodine value.
ঘ) Molecular weight of triglycerides → Determined by saponification value, not PV.

1.Partial hydrogenation of vegetable oils involves adding hydrogen to some of the double bonds in unsaturated fatty acids using a catalyst (like Ni).
2.During this process:
     Cis double bonds can isomerize to trans configuration, forming trans-fatty acids.
     This occurs especially at moderate hydrogenation levels.
3.Complete hydrogenation converts all double bonds to single bonds, producing fully saturated fats without trans fats.
 
Other options:
খ) Complete saturation without trans fats → Only occurs in full hydrogenation, not partial.
গ) Higher iodine value → Hydrogenation reduces iodine value as unsaturation decreases.
ঘ) Increased free fatty acids → Hydrogenation does not increase FFA; FFA formation is from hydrolysis.

1.When the seed particles are smaller, their surface area increases, giving the solvent (like hexane) more access to the oil inside the seeds.
2.This accelerates the extraction process, allowing more oil to be removed in less time.
3.It does not reduce solubility, degrade oil quality, or significantly affect moisture content.

1.In alkyd resin-based paints, the term “oil length” indicates the proportion of oil (fatty acid component) relative to the total resin solids in the paint.
2.High oil length paints (usually >50% oil) dry slower, have better gloss, and are more flexible.
3.Low oil length paints (<40% oil) dry faster and are harder but less flexible.
4.It is not related to pigment molecular weight, drying time directly, or solvent viscosity.

1.Titanium dioxide (TiO₂) exists mainly in anatase and rutile forms.
2.Rutile TiO₂ is preferred in paints because it has:
     Superior UV resistance, protecting the paint film from degradation.
     Better durability outdoors, resisting chalking and fading.
3.Anatase has slightly higher photocatalytic activity, which can degrade paint binders, making it less suitable for outdoor paints.
4.The refractive index of rutile is actually higher, not lower.
5.Drying rate and density are not primary reasons for choosing rutile in pigments.