Answers:

• Why scum forms: Soap anions (RCOO⁻) react with Ca²⁺/Mg²⁺ ions in hard water to form insoluble calcium or magnesium salts (scum) which precipitate out and reduce cleaning efficiency.
• Why detergents preferred:
  • Detergents contain sulphonate or sulfate groups that remain soluble in hard water and do not form insoluble precipitates with Ca²⁺/Mg²⁺.
  • They can be formulated for specific cleaning tasks and work effectively at lower concentrations and in colder water.

Answers:

• Suggested ester: Ethyl ethanoate (ethyl acetate) — commonly smells like pears or fruity notes.
• Formation equation: CH₃CH₂OH + CH₃COOH ⇌ CH₃COOCH₂CH₃ + H₂O (conc. H₂SO₄ catalyst).
• Catalyst and reason for smell: Concentrated sulfuric acid is used as catalyst and dehydrating agent; esters are often volatile with molecular structures that interact with olfactory receptors producing pleasant fruity odours.

Answers:

• Products:
  • Complete combustion — CO₂ and H₂O (e.g., CH₄ + 2O₂ → CO₂ + 2H₂O).
  • Incomplete combustion — CO, C (soot) and partially oxidised hydrocarbons.
• Hazard: Carbon monoxide (CO) is toxic (binds haemoglobin), soot causes respiratory issues and incomplete combustion indicates inefficient fuel use; ensure adequate oxygen supply and ventilation to prevent hazards.

Answers:

• Oxidation sequence:
  • CH₃CH₂OH (ethanol) —[O]→ CH₃CHO (ethanal) —[O]→ CH₃COOH (ethanoic acid).
  • Common reagents: Acidified K₂Cr₂O₇ or KMnO₄.
• Stop at ethanal: Use controlled, mild oxidation conditions and remove aldehyde as it forms (distillation) to prevent further oxidation to acid; use milder oxidants and lower temperatures.

Answers:

• Saponification equation: Triglyceride (fat) + 3 NaOH → Glycerol + 3 RCOONa (soap).
• Products and roles:
  • Glycerol — a byproduct used in cosmetics and as a humectant.
  • Sodium salts of fatty acids (soap) — act as surfactants to emulsify oils/dirt enabling removal with water.

Answers:

• Reflux purpose: Ensures reactants react at elevated temperature while preventing loss of volatile compounds; allows reaction to reach equilibrium.
• Removal of water: According to Le Chatelier's principle, removing water (a product) shifts equilibrium towards ester formation, increasing yield; distillation helps separate and collect the ester once formed.

Answers:

• Odour reason: Ethanoic acid is volatile and has a polar —COOH group that interacts strongly with olfactory receptors; its acidic nature adds to the sharp vinegar‑like smell compared to the milder smell of ethanol.
• Safety steps:
  • Ventilate the area and avoid inhaling vapours.
  • Wear gloves and clean with water and baking soda (mild base) to neutralise small spills; dispose of waste per lab guidelines.

Answers:

• Types of isomerism: Structural (chain and position) isomerism and because C₄H₈ is unsaturated, it can exhibit cis‑trans (geometric) isomerism if it contains a C=C with different substituents.
• Two structural isomers: 1‑butene (CH₂=CH–CH₂–CH₃) and 2‑butene (CH₃–CH=CH–CH₃) — 2‑butene also has cis/trans isomers.

Answers:

• Aldehyde reaction: Aldehydes are easily oxidised to carboxylic acids; they reduce Ag⁺ in Tollens' reagent to metallic silver, forming a silver mirror.
• Ketone behaviour: Ketones are less susceptible to oxidation under mild conditions and therefore do not reduce Ag⁺; they usually give a negative Tollens' test.

Answers:

• Reason: While the —OH group can hydrogen bond with water, the non‑polar hydrocarbon chain is hydrophobic; as chain length increases, hydrophobic character dominates and reduces solubility.
• Most soluble: Ethanol is most soluble (completely miscible) because its short chain makes the polar —OH group's effect dominant.

Answers:

• Effects:
  • Increasing concentration of reactants increases collision frequency and rate.
  • Raising temperature speeds up rate but may affect equilibrium (often faster forward and reverse rates).
  • Catalyst (H₂SO₄) increases rate by providing an alternate pathway without being consumed.
• Practical yield increase: Use excess alcohol or remove water as formed (e.g., using a drying agent or azeotropic distillation) to shift equilibrium toward ester products.

Answers:

• IUPAC name: Propan‑2‑ol (commonly isopropanol).
• Functional group: —OH (alcohol); the carbon bearing —OH is attached to two other carbons, so it is a secondary alcohol.

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• Biodegradability: Natural fats are triglycerides of fatty acids which microorganisms can metabolise, breaking down soap molecules into CO₂, water and biomass; biodegradable soaps often have simpler structures amenable to microbial enzymes.
• Chain length effects:
  • Shorter chains yield soaps that are more soluble and produce more lather but may be harsher.
  • Longer chains improve cleansing of oily dirt (stronger hydrophobic interaction) but may be less soluble and harder (solid soap).

Answers:

• Recommendation: Detergent is more suitable because it remains effective in hard water and at lower temperatures; its surfactant head groups do not precipitate with Ca²⁺/Mg²⁺.
• Environmental consideration: Some synthetic detergents are not readily biodegradable and can cause eutrophication or persistent pollution; choose biodegradable formulations and proper waste treatment.

Answer — 6‑point checklist:

• Understand tetravalency and catenation as reasons for carbon’s diversity.
• Remember general formulas and examples for alkanes, alkenes; know isomerism basics.
• Know functional groups —OH, —COOH, —COOR and typical reactions (oxidation, esterification, saponification).
• Practice writing balanced equations for combustion, esterification and saponification.
• Recall physical property trends: solubility, boiling point influences (H‑bonding, chain length, branching).
• Safety: handle oxidising agents and strong acids/bases with care; ensure ventilation for combustion experiments; neutralise spills appropriately.