90. Treatment of phenol with sodium hydroxide and then carbon dioxide gives which acid after work-up?
[AIEEE Chemistry — 2009]
(A) Benzoic acid
(B) Salicylaldehyde
(C) Salicylic acid
(D) Phthalic acid
Answer: (C) Salicylic acid
Explanation: The Kolbe–Schmitt reaction introduces a carboxyl group onto a phenoxide ring, mainly at the ortho position under suitable conditions. Acidification produces salicylic acid, also known as 2-hydroxybenzoic acid. The reaction connects aromatic phenols and important organic carboxylic acids.
89. Which liquid forms a fruity-smelling ester when mixed with ethanol and concentrated sulphuric acid?
[AIEEE Chemistry — 2009]
(A) Methanol
(B) Formaldehyde
(C) Acetone
(D) Acetic acid
Answer: (D) Acetic acid
Explanation: Acetic acid reacts reversibly with ethanol in the presence of concentrated sulphuric acid to form ethyl ethanoate and water. Ethyl ethanoate is a volatile ester with a characteristic fruity odour. Sulphuric acid catalyses the Fischer esterification reaction.
88. What is the rate-determining step of the Cannizzaro reaction of benzaldehyde?
[AIEEE Chemistry — 2009]
(A) Hydride transfer to another carbonyl molecule
(B) Removal of a proton from a carboxylic acid group
(C) Hydroxide attack on a carboxylate group
(D) Removal of the benzyl alcohol proton
Answer: (A) Hydride transfer to another carbonyl molecule
Explanation: Hydroxide first attacks the benzaldehyde carbonyl, creating a tetrahedral intermediate. The crucial slow step transfers a hydride from that intermediate to a second aldehyde molecule. This produces the reduced alcohol and an oxidised carboxylate after the subsequent proton-transfer steps.
87. What is Bisphenol A (BPA)?
[UPSC CSE Prelims — 2008]
(A) A diagnostic test for cancer
(B) A test for performance-enhancing drugs in athletes
(C) A chemical used to develop food-packaging materials
(D) A specialised steel alloy
Answer: (C) A chemical used to develop food-packaging materials
Explanation: Bisphenol A is an organic industrial compound used to produce polycarbonate plastic and epoxy resins. Certain containers and protective food-can coatings historically used these materials. BPA is not a medical test or steel alloy, and its possible hormonal effects have prompted safety scrutiny.
86. A mixture of which gases is responsible for most explosions in coal mines?
[UPSC CSE Prelims — 2008]
(A) Hydrogen and oxygen
(B) Oxygen and acetylene
(C) Methane and air
(D) Carbon dioxide and methane
Answer: (C) Methane and air
Explanation: Coal seams may release methane, a flammable hydrocarbon. When it accumulates with oxygen-containing air within an ignitable range, an ignition source can trigger a mine explosion. Ventilation and gas detection are crucial safeguards. Carbon dioxide itself does not act as a combustible fuel.
85. Reductive ozonolysis of but-2-ene with ozone followed by zinc and water gives which product?
[AIEEE Chemistry — 2008]
(A) Propanal
(B) Propanone
(C) Butan-2-one
(D) Ethanal
Answer: (D) Ethanal
Explanation: But-2-ene has a symmetrical internal double bond. Cleavage of this bond by ozone followed by a reductive work-up gives two molecules of ethanal. Ketones or larger aldehydes would require differently substituted double-bonded carbons in the starting alkene.
84. Nitration of toluene, reduction of the nitro groups, diazotisation, and treatment with cuprous bromide produces which mixture?
[AIEEE Chemistry — 2008]
(A) Ortho- and para-bromotoluene
(B) Ortho- and para-dibromobenzene
(C) Ortho- and para-bromoaniline
(D) Ortho- and meta-bromotoluene
Answer: (A) Ortho- and para-bromotoluene
Explanation: Toluene nitration initially produces mainly ortho and para derivatives. Reduction converts nitro groups to amino groups; diazotisation followed by the Sandmeyer reaction substitutes bromine for the amino-derived diazonium group. Consequently, the final mixture mainly contains ortho- and para-bromotoluenes.
83. Which statement about natural and synthetic rubber is false?
[AIPMT Chemistry — 2008]
(A) Buna-S is a butadiene-styrene copolymer
(B) Natural rubber is a 1,4-polymer of isoprene
(C) Vulcanisation forms sulphur bridges between polymer chains
(D) Natural rubber has a trans configuration at every double bond
Answer: (D) Natural rubber has a trans configuration at every double bond
Explanation: Natural rubber is predominantly cis-1,4-polyisoprene, not the trans form described in the last statement. The cis configuration contributes to elasticity. Buna-S is a butadiene-styrene copolymer, and vulcanisation forms sulphur cross-links that improve toughness and resilience.
82. Which aldehyde reacts with phenol to produce Bakelite resin?
[AIEEE Chemistry — 2008]
(A) Ethylene glycol
(B) Acetaldehyde
(C) Acetone
(D) Formaldehyde
Answer: (D) Formaldehyde
Explanation: Bakelite is a phenol-formaldehyde thermosetting resin. Reactions of phenolic aromatic sites with formaldehyde lead to methylene-linked networks that become rigid on curing. Acetone is a ketone and ethylene glycol is a diol, so neither is the standard aldehyde used for this polymer.
81. By which other name is the compound RDX known?
[UPSC CSE Prelims — 2007]
(A) Cyanohydrin
(B) Dextran
(C) Cyclohexane
(D) Cyclonite
Answer: (D) Cyclonite
Explanation: Cyclonite is a common alternative name for RDX, an energetic cyclic nitramine compound. The other options designate unrelated substances: cyanohydrins are compounds bearing hydroxyl and cyano groups, dextran is a polysaccharide, and cyclohexane is a saturated six-carbon hydrocarbon.
