Detergents and Soap is part of Chemistry. Below are notes on 8 sub-topics, followed by practice MCQs from State PSC and UPSC papers.
Additives in Soaps and Detergents: Builders, Brighteners, Enzymes, Perfumes, Germicides
- Builders: Additives that enhance cleaning efficiency, soften hard water, maintain pH, or improve detergent formulation.
- Sodium Sulphate: Added to detergent powders to keep them dry and prevent caking.
- Sodium Silicate: Included in detergents to maintain alkalinity, prevent corrosion of metal parts of washing machines, and contribute to powder dryness.
- Brighteners (Optical Brighteners/Fluorescent Whitening Agents): Absorb ultraviolet light and re-emit it as visible blue light, making fabrics appear whiter and brighter by counteracting yellowing.
- Enzymes: Biological catalysts (e.g., proteases, lipases, amylases) added to break down specific stains like proteins, fats, and starches, improving cleaning efficacy, especially at lower temperatures.
- Perfumes (Fragrances): Incorporated to impart a pleasant scent to the detergent and washed clothes, masking chemical odors.
- Germicides (Antimicrobial Compounds): Added to provide antibacterial and disinfectant properties to soaps and detergents.
- Triclosan: An antimicrobial agent commonly found in toiletries and personal care products such as antibacterial soaps, toothpastes, and deodorants. High levels or long-term exposure are considered potentially harmful.
- Triclocarban: Another antimicrobial compound used in personal care products, including soaps, lotions, deodorants, and toothpastes.
Advantages of Synthetic Detergents over Soaps
- Effective in hard water: Do not form insoluble precipitates with calcium (Ca²⁺) and magnesium (Mg²⁺) ions present in hard water, unlike soaps which form scum.
- Stable in acidic solutions: Function effectively in acidic water, whereas soaps decompose to insoluble fatty acids.
- Higher solubility: Generally more soluble and effective in cold water compared to soaps.
Chemistry of Saponification: Oils, Fats, and Alkali
- Saponification: Hydrolysis of an ester (oils/ fats, which are triglycerides) by an alkali to produce soap and glycerol.
- Oils/Fats are esters of glycerol and longchain fatty acids.
- Soap is the sodium or potassium salt of longchain fatty acids (e.g., Stearic acid, Oleic acid, Palmitic acid).
- Sodium hydroxide (NaOH) is used to produce hard soaps (e.g., bar soaps).
- Potassium hydroxide (KOH) is used to produce soft soaps (e.g., liquid soaps, shaving creams).
- The by-product of saponification is Glycerol (propane-1,2,3-triol).
- Historically, mixing ashes (source of alkali, primarily K2CO3) with animal fat (triglyceride) produced crude soap.
- Saponification is the fundamental process used in soap making.
Comparison of Soaps and Synthetic Detergents
- Soaps: Sodium/Potassium salts of long-chain fatty acids. Detergents: Sodium salts of longchain sulphonic acids (e.g., alkyl sulphonates, alkylbenzene sulphonates).
- Soaps: Derived from vegetable oils/animal fats (saponification). Detergents: Synthesized from petrochemicals.
- Soaps in Hard Water: React with Ca²⁺/Mg²⁺ ions to form insoluble precipitates (scum), reducing lather and cleaning action.
- Detergents in Hard Water: Form soluble salts with Ca²⁺/Mg²⁺ ions, thus lather well and clean effectively.
- Soaps in Acidic Medium: Decompose into insoluble fatty acids, losing cleaning efficacy.
- Detergents in Acidic Medium: Are more stable and effective than soaps.
- Overall Effectiveness: Soaps are effective only in soft and neutral/alkaline water. Detergents are effective in soft, hard, and acidic water.
- Detergents do not possess all properties of soaps (e.g., raw material source, performance in hard/acidic water).
Definition and Classification of Soaps
- Soaps are sodium (hard soap) or potassium (soft soap) salts of long-chain fatty acids.
- Soft Soaps: Potassium salts of fatty acids; known for producing more lather; used in shaving creams and liquid soaps.
- Hard Soaps: Sodium salts of fatty acids; typically solid; used in bathing and laundry bars.
- Transparent Soaps: Manufactured by dissolving regular soap in ethanol and then evaporating the excess solvent; often contain glycerol to prevent rapid drying.
- Shaving Soaps: Primarily contain potassium salts of fatty acids (for soft lather); include glycerol (prevents rapid drying); sodium rosinate (enhances lather); borax (softens water, mild antiseptic); and sometimes fillers like sodium silicate or sodium carbonate.
- Soap Chips: Produced by running a thin sheet of melted soap onto a cool cylinder and then scraping off the dried soap in small, broken pieces.
Definition and Classification of Synthetic Detergents (Anionic, Cationic, Non-ionic)
- Synthetic detergents are cleansing agents effective in hard water, unlike soaps which form scum.
- They are primarily classified based on the nature of the active hydrophilic group.
- 1. Anionic Detergents:
- Active part of the molecule is the anion.
- Typically sodium alkyl sulphates (e.g., Sodium Lauryl Sulphate, CH₃(CH₂)₁₀CH₂OSO₃⁻Na⁺) or sodium alkylbenzene sulphonates (e.g., Sodium Dodecylbenzenesulphonate).
- Used in toothpaste, laundry products, and household cleaning.
- The cleaning action is due to the sulfonate (–SO₃⁻) or sulfate ester (–OSO₃⁻) group.
- Linear alkyl chain anionic detergents are biodegradable; branched chain ones are not.
- 2. Cationic Detergents:
- Active part of the molecule is the cation.
- Usually quaternary ammonium salts of amines with chlorides, bromides, or acetates.
- Example: Cetyltrimethylammonium bromide ([CH₃(CH₂)₁₅–N⁺(CH₃)₃]Br⁻).
- Possess germicidal properties.
- Used in hair conditioners and as germicides.
- 3. Non-ionic Detergents:
- Do not contain any ions in their structure or when dissolved in water.
- Typically esters of high molecular mass alcohols or fatty acids with polyoxyethylene glycols.
- Example: Polyoxyethylene stearate (CH₃(CH₂)₁₆COO(CH₂CH₂O)nCH₂CH₂OH), formed by the reaction of stearic acid with polyethylene glycol.
- Used in dishwashing liquids and liquid laundry detergents.
- Key Distinction: Soaps are alkali metal salts of long-chain fatty acids (e.g., Sodium stearate, CH₃(CH₂)₁₆COO⁻Na⁺), while synthetic detergents have different hydrophilic heads (sulfonate, quaternary ammonium, or polyether).
- Detergents for cleaning clothes are commonly sulfonates (anionic detergents).
- Alconox is an example of a biodegradable detergent often used for cleaning glassware.
- Primary classifications of synthetic detergents are Anionic, Cationic, and Non-ionic. "Natural Detergents" and "Polyionic Detergents" are not standard primary types of synthetic detergents.
Manufacturing Processes of Soaps
- Soaps are sodium or potassium salts of longchain fatty acids.
- Manufacturing process is Saponification: Hydrolysis of fats/oils (triglycerides) with a strong alkali (NaOH for hard soap, KOH for soft soap).
- Reaction: Triglyceride (fat/oil) + Alkali (NaOH/KOH) → Soap + Glycerol.
- Glycerol (propane-1,2,3-triol) is a valuable by-product.
- After saponification and 'salting out' (adding NaCl to precipitate soap), the aqueous layer left is called 'spent lye'.
- Spent lye contains glycerol, excess alkali, and dissolved salts.
- Glycerol is separated from spent lye by purification methods, primarily using distillation under reduced pressure to recover it, as glycerol can decompose at its normal boiling point under atmospheric pressure.
Mechanism of Cleansing Action of Soaps: Micelle Formation
- Soap molecules consist of a hydrophilic (water-loving) head (ionic part, e.g., COO⁻Na⁺) and a hydrophobic (water-hating) tail (long hydrocarbon chain).
- In water, the hydrophobic tail interacts with oily/greasy dirt particles, while the hydrophilic head faces the water.
- Micelle formation: Soap molecules aggregate, forming spherical structures called micelles around the dirt/oil.
- Inside the micelle, the hydrophobic tails are clustered, encapsulating the oily dirt droplet.
- The hydrophilic heads of the soap molecules point outwards into the surrounding water.
- This encapsulation of dirt by micelles, suspending it in water, is known as emulsification.
- The negatively charged hydrophilic heads on the micelle surface repel each other, keeping the micelles (and trapped dirt) suspended in water, preventing re-deposition.
- The cleansing action is primarily due to the formation of these micelles, which trap and remove oil/grease.
- Micelles are colloidal particles and scatter light (Tyndall effect).
- Soaps are typically sodium or potassium salts of long-chain carboxylic acids. (Not ammonium or sulfonate salts).
- In hard water (containing Ca²⁺ or Mg²⁺ ions), soaps react to form insoluble precipitates (scum/lather), rather than forming micelles around these ions, which reduces cleansing efficiency.
- Soap with water can form lyotropic liquid crystals.
- Soaps clean surfaces primarily by reducing surface tension and enabling emulsification of dirt.
20. The Fertilizers
Practice MCQs: Detergents and Soap
Additives in Soaps and Detergents: Builders, Brighteners, Enzymes, Perfumes, Germicides
'Triclosan', considered harmful when exposed to high levels for a long time, is most likely present in which of the following?
Asked in: UPSC IAS 2021
- Food preservatives
- Fruit-ripening substances
- Reused plastic containers
- Toiletries
Show answer
Answer: D. Toiletries
- Triclosan is an antimicrobial agent. - It was commonly added to antibacterial soaps, toothpastes, mouthwashes, and other personal care products. - Concerns exist regarding its health effects and environmental impact.
Consider the following statements The purpose of adding sodium sulphate and sodium silicate to the detergent in a washing powder is To keep the washing powder dry To maintain the alkalinity of the powder Which of these statements is/are correct?
Asked in: UPPCS Prelims 2003
- Only 1
- Only 2
- Both 1 and 2
- Neither 1 nor 2
Show answer
Answer: C. Both 1 and 2
Sodium sulphate (Na2SO4) is used in washing powders as a filler and also acts as an anti-caking agent, helping to keep the powder dry and free- flowing. Thus, statement 1 is correct. Sodium silicate (Na2SiO3) is a common builder in detergents. It helps to maintain alkalinity by acting as a buffer and also improves the cleaning performance by softening water (sequestering calcium and magnesium ions) and preventing soil redeposition. Thus, statement 2 is correct as it maintains the alkalinity of the powder solution.
Which of the following chemical is added in washing powder for keeping it dry?
Asked in: Headmaster (Secondary School) 2018
- Sodium silicate
- Inorganic phosphate
- Carboxy – methyl cellulose
- Sodium perborate
Show answer
Answer: A. Sodium silicate
Sodium silicate is an ingredient in washing powders that acts as a builder and aids in cleaning, and also has anti-corrosive properties.
Which one of the following has been used as antimicrobial compound in personal care products like soaps, lotions, deodorants and toothpastes?
Asked in: ASCO 2014
- Triclocarban
- Chlorine
- Benzoyl Peroxide
- Hydrogen Peroxide
Show answer
Answer: A. Triclocarban
HORTICULTURE DEVELOPMENT OF‐ FICER(HDO) -2015 Triclocarban is commonly used as an antimicrobial compound in personal care products.
Which one of the following has been used as antimicrobial compound in personal care products like soaps, lotions, deodorants and toothpastes? - [A] Triclocarban - [C] Benzoyl Peroxide - [B] Chlorine - [D] Hydrogen Peroxide
Asked in: POST GRADUATE TEACHER (PGT) 2018
- Triclocarban
- Chlorine
- Benzoyl Peroxide
- Hydrogen Peroxide
Show answer
Answer: A. Triclocarban
Triclocarban is a synthetic antimicrobial compound. Benzoyl peroxide is typically used for acne treatment, chlorine is a disinfectant but not commonly in such personal care items, and hydrogen peroxide is an antiseptic with a more limited application in these products.
Which one of the following has been used as antimicrobial compound in personal care products like soaps, lotions, deodorants and toothpastes?
Asked in: POST GRADUATE TEACHER (PGT) 2018
- [A]Triclocarban
- [B] Chlorine
- [C]Benzoyl Peroxide
- [D] Hydrogen Peroxide
Show answer
Answer: A. [A]Triclocarban
Triclocarban is an antibacterial agent that works by disrupting bacterial cell membranes and inhibiting key enzymes. Its inclusion in personal care products aims to reduce odor-causing bacteria and enhance hygiene.
Advantages of Synthetic Detergents over Soaps
Point out incorrect statement.
Asked in: WBCS Main Paper 4 2022
- Detergent works well even with hard water.
- Detergent does not form any precipitate with hard water.
- Detergent is easily soluble in water.
- Detergent is fully biodegradable.
Show answer
Answer: D. Detergent is fully biodegradable.
While some modern detergents are designed to be biodegradable, many older or synthetic detergents are not fully biodegradable and contribute to water pollution. Soaps, derived from natural fats, are generally more biodegradable than synthetic detergents.
Chemistry of Saponification: Oils, Fats, and Alkali
Soap is sodium or potassium salt of
Asked in: UPSC NDA 1 2016
- Stearic acid
- Oleic acid
- Palmitic acid
- All of the above
Show answer
Answer: D. All of the above
Soaps are salts of fatty acids. Saponification involves reacting fats/oils (triglycerides of fatty acids) with a strong base (NaOH or KOH) to produce soap (fatty acid salt) and glycerol.
What is the specific purpose of using potassium hydroxide during the saponification process ?
Asked in: UPSC NDA 1 2023
- To obtain soaps which are hard on the skin
- To obtain soaps which are soft on the skin
- To obtain natural fragrance
- To make the saponification very economical
Show answer
Answer: B. To obtain soaps which are soft on the skin
- Saponification uses a strong base to hydrolyze fats/oils. - NaOH produces hard soaps. - KOH produces soft or liquid soaps. - The softness of the soap is desirable for certain applications like liquid soaps or those used on the skin.
If one mixes up ashes with animal fat, the substance received in the crude form is called
Asked in: UPSC NDA 2 2016
- Pheromone
- Soap
- Cement
- Concrete
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Answer: B. Soap
- Soap is made through saponification, a reaction between fats/oils and an alkali. - Animal fat provides triglycerides. - Ashes, particularly from wood, can provide alkali (potassium carbonate/ hydroxide) when mixed with water. - This historical process yields crude soap.
In the production of soap, by-product is
Asked in: School Lecturer 2015
- Fatty acid
- Sodium hydroxide
- Sodium salts
- Glycerol
Show answer
Answer: D. Glycerol
Glycerol is a sweet, viscous liquid that is a byproduct of soap manufacturing. The reaction is a hydrolysis of esters.
The saponification is used in which of the following?
Asked in: Computer Programmer 2021
- The process of making rocket propellants
- The process of deep sea research
- The process of soap making
- The process of covid recovery
Show answer
Answer: C. The process of soap making
Knowledge of fundamental chemical processes and their applications is crucial for the science section of the UPSC exam. Saponification is a well-known chemical reaction with a direct practical application.
Comparison of Soaps and Synthetic Detergents
Which is NOT correct for detergents ?
Asked in: OPSC CS Prelims 2019
- Have all properties of soaps
- Can be used in soft and hard water
- Cannot be used in acidic medium
- Generally obtained from vegetable oil
Show answer
Answer: D. Generally obtained from vegetable oil
- Detergents are synthetic surfactants, usually derived from petrochemicals. - Soaps are alkali salts of fatty acids, obtained from the saponification of natural fats and oils (like vegetable oil or animal fat).
Assertion (A): Synthetic detergents can lather well in hard water. Reason (R): Synthetic detergents form soluble calcium and magnesium salts with hard water.
Asked in: UPPCS Prelims 2002
- Both A and R are individually true and R is the correct explanation of A
- Both A and R are individually true but R is not a correct explanation of A
- A is true but R is false
- A is false but R is true
Show answer
Answer: A. Both A and R are individually true and R is the correct explanation of A
- Assertion (A) is true: Synthetic detergents are effective and can lather well even in hard water (water containing high concentrations of dissolved minerals like calcium and magnesium ions). - Reason (R) is true: Unlike traditional soaps, which react with calcium and magnesium ions in hard water to form insoluble precipitates (scum), synthetic detergents form soluble complexes or salts with these ions.
Definition and Classification of Soaps
Which of the following statements about the types of soaps is/are TRUE? Transparent soaps are made by dissolving the soap in ethanol and then evaporating the excess solvent. Shaving soaps contain fillers like sodium rosinate, sodium silicate, borax and sodium carbonate. Soap chips are made by running a thin sheet of melted soap onto a cool cylinder and scraping off the soaps in small broken pieces. Choose the correct answer from the options given below:
Asked in: HAS Prelims 2022
- 1 and 2 only
- 2 only
- 1 and 3 only
- 2 and 3 only
Show answer
Answer: C. 1 and 3 only
Different types of soaps have specific formulations and manufacturing processes adapted to their intended use (e.g., transparency, lather stability, cleaning efficiency).
A sample of 'soft soap' contains
Asked in: UPSC NDA 2 2019
- Caesium
- Potassium
- Calcium
- Magnesium
Show answer
Answer: B. Potassium
- Soap is produced by the saponification of fats or oils with a strong alkali. - Hard soaps use sodium hydroxide (NaOH) as the alkali, resulting in sodium salts of fatty acids. - Soft soaps use potassium hydroxide (KOH) as the alkali, resulting in potassium salts of fatty acids.
Definition and Classification of Synthetic Detergents (Anionic, Cationic, Non-ionic)
Detergents used for cleaning clothes are
Asked in: BPSC Prelims Exam 63rd
- carbonates
- bicarbonates
- bismuthates
- sulfonates
Show answer
Answer: D. sulfonates
Detergents are synthetic cleaning agents distinct from soaps, which are salts of fatty acids. The primary active cleaning component in many detergents is a sulfonate-based surfactant.
Which one of the following is NOT a synthetic detergent ?
Asked in: UPSC NDA 1 2019
- CH$_3$(CH$_2$)$_{10}$CH$_2$O SO$_3^{-}$ Na$^{+}$
- [CH$_3$(CH$_2$)$_{15}$–N–(CH$_3$) $_3$]$^{+}$ Br$^{-}$
- CH$_3$(CH$_2$)$_{16}$COO$^{-}$ Na$^{+}$
- CH$_3$(CH$_2$) $_{16}$COO(CH$_2$CH$_2$O)$_n$ CH$_2$CH$_2$OH
Show answer
Answer: C. CH$_3$(CH$_2$)$_{16}$COO$^{-}$ Na$^{+}$
Synthetic detergents are cleaning agents that are synthesized and have chemical structures different from traditional soaps. Traditional soaps are salts of fatty acids, typically with a carboxylate head group (-COO-). Option C, CH$_3$(CH$_2$) $_{16}$COO$^{-}$ Na$^{+}$, is sodium stearate, which is a common example of a soap. Options A, B, and D represent synthetic detergents with different types of polar head groups: A is an anionic sulfate-based detergent, B is a cationic quaternary ammonium-based detergent, and D is a non-ionic polyoxyethylene-based detergent.
Which biodegradable detergent used for the cleaning of glassware?
Asked in: JUNIOR laboratory assistant 2025
- Alcosoap
- Alconox
- Polysorbate
- All of the above
Show answer
Answer: D. All of the above
Biodegradable detergents are preferred in laboratory settings to minimize environmental impact. They are effective in removing a wide range of residues from glassware.
Which of the following is not a type of the synthetic detergent ?
Asked in: Co operative Supervisor & Environment Supervisor (Group C) Exam 2023
- Natural Detergents
- Anionic Detergents
- Cationic Detergents
- Polyionic Detergents
Show answer
Answer: A. Natural Detergents
Synthetic detergents are designed to have better cleaning properties than traditional soaps and are more effective in hard water. Their classification is crucial for understanding their applications and properties.
Manufacturing Processes of Soaps
In Soap Industry Glycerol can be separated from Spent Lye by - - (5) Question not attempted
Asked in: Department Recruitment 2024 (Chemist) 2024
- Distillation under reduced pressure
- Fractional Distillation
- Steam Distillation
- Sublimation
Show answer
Answer: A. Distillation under reduced pressure
Glycerol is a high-boiling point compound that can decompose at high temperatures. Vacuum distillation reduces the boiling point, enabling separation without degradation.
Mechanism of Cleansing Action of Soaps: Micelle Formation
साबुन की सफाई ͩक्रया के संदिभर्त में सही कथन चुǓनए : A. साबुन के अणुओं का जलरिागी ͧसरिा ेल के कणों के सम्पकर्त में आा है। B. कपड़िों की सफाई के दिौरिान साबुन के घोल में ͧमसेल का Ǔनमार्तण इमल्सीकरिण कहलाा है। C. ͧमसेल Ǔनमार्तण के दिौरिान साबुन के अणुओं का जलरिागी ͧसरिा अन्दिरि की ओरि होा है। D. कठोरि जल में ͧमसेल ेल के कणों के बदिले Ca²⁺ या Mg²⁺ आयनों को घेरिे हैं।
Asked in: HAS Prelims 2021
- A, B और C
- A और D
- B और C
- B, C और D
Show answer
Answer: C. B और C
साबुनि के अणु में एक जलरागी (hydrophilic) lसरा (आयlनिक या ध्रुवीय) और एक जलlवरागी (hydrophobic) lसरा (लंबी हाइड्रोकाबर्तनि श्रृंखला) होता है। ये दोहरे गुण साबुनि को तेल और पानिी दोनिों के साथ अंतःlक्रिया करनिे में मदद करते हैं।
Select the correct statements regarding cleansing action of soap.
Asked in: HAS Prelims 2021
- Hydrophilic end of soap molecules in‐ teract with the oily droplets.
- The formation of micelles in a soap solution during the cleaning of clothes is called emulsification.
- The hydrophobic end of the soap mo‐ lecules is in the inner side during micelle formation.
- Micelles surround the Ca²⁺ or Mg²⁺ ions in hard water instead of oily droplets. A. A, B and C B. A and D C. B and C D. B, C and D
Show answer
Answer: C. The hydrophobic end of the soap mo‐ lecules is in the inner side during micelle formation.
Soap molecules are amphipathic, having a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. This structure is key to their cleansing action, which involves forming micelles.
The cleaning action of soap and detergent in water is due to the formation of
Asked in: UPSC NDA 1 2015
- Micelle
- Salt
- Base
- Acid
Show answer
Answer: A. Micelle
Soap and detergent molecules have a hydrophilic (water-attracting) head and a hydrophobic (oil/ grease-attracting) tail. In water, these molecules aggregate into spherical structures called micelles, where the hydrophobic tails are oriented inward, away from the water, and the hydrophilic heads are oriented outward, in contact with the water. Oily or greasy dirt particles get trapped within the hydrophobic core of these micelles and are thus suspended in water, allowing them to be washed away.
Which one of the following statements about the cleansing action of soap is not true ?
Asked in: UPSC NDA 1 2021
- The oil and dirt gets collected in the centre of the micelle.
- Soap micelles scatter light.
- Soaps are ammonium salts of long chain carboxylic acids.
- Soap forms insoluble precipitates with the calcium and magnesium ions in hard water.
Show answer
Answer: C. Soaps are ammonium salts of long chain carboxylic acids.
Soaps function through the formation of micelles, aggregates of soap molecules in water, where the hydrophobic tails face inwards, dissolving oils and dirt, and the hydrophilic heads face outwards, interacting with water. Micelles are large enough to scatter light, a phenomenon known as the Tyndall effect. Soaps react with calcium and magnesium ions present in hard water to form insoluble precipitates called scum, which reduces their effectiveness.
Soap with water forms :
Asked in: UPSC NDA 1 2024
- Metallotropic liquid crystal
- Thermotropic liquid crystal
- Homogeneous solution
- Lyotropic liquid crystal
Show answer
Answer: D. Lyotropic liquid crystal
Soap molecules are amphiphilic, having a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. In water, they aggregate into structures like micelles, bilayers, or vesicles depending on concentration and temperature. These ordered structures often exhibit liquid crystalline phases, which are classified as lyotropic because their formation depends on the concentration of the solute (soap) in the solvent (water).
Soaps clean surfaces on the principle based on
Asked in: UPSC NDA 2 2019
- Viscosity
- Floatation
- Elasticity
- Surface tension
Show answer
Answer: D. Surface tension
- Soaps are surfactants. - Surfactants reduce the surface tension of water. - Reduced surface tension allows water to spread and penetrate effectively. - Soap molecules emulsify grease and dirt by forming micelles. - The fundamental principle involves the interaction of soap at surfaces (related to surface tension).
Soap and detergents help remove dirt from cloths. It does so because of having two parts :
Asked in: OPSC CS Prelims 2016
- Hydrophilic, neutrophilic
- Both the hydrophobic
- Hydrophilic and hydrophobic
- Neutrophilic, hydrophobic
Show answer
Answer: C. Hydrophilic and hydrophobic
The cleaning action of soaps and detergents is due to their amphipathic structure, allowing them to bridge the gap between water and nonpolar substances like grease.
Cleansing action of soap occurs because
Asked in: PPSC CS Prelims 2015
- Oil and grease can be absorbed into the hydro‐ phobic centres of soap micelles and washed away.
- Oil and grease can be absorbed into the hydro‐ philic centres of soap micelles and washed away.
- Oil and grease can be absorbed into both hy‐ drophilic and hydrophobic centres but not washed away.
- Cleansing action is not related to micelles.
Show answer
Answer: A. Oil and grease can be absorbed into the hydro‐ phobic centres of soap micelles and washed away.
- Soap molecules are surfactants, possessing a dual nature: a hydrophilic (water-attracting) head and a hydrophobic (oil-attracting) tail. - In water, these molecules aggregate to form micelles, which are spherical structures where the hydrophobic tails point inward, away from the water, forming a non- polar core. The hydrophilic heads face outward towards the water. - When soap is added to water containing oil or grease (which are non-polar), the hydrophobic tails of the soap molecules dissolve in the oil/grease droplets. - These oil/grease droplets become surrounded by soap molecules with their hydrophilic heads facing the water, forming an emulsion. The oil/grease is effectively trapped within the hydrophobic core of these new micelles. - Because the outer surface of these micelles is hydrophilic, they become soluble or easily suspended in water and can be rinsed away, carrying the dirt (oil/grease) with them.