Chemistry
- The compound that will undergo S_N1 reaction with the fastest rate is Answer: 1. [structure: 1-bromoethylbenzene (phenyl-CH(CH ₃ )-Br), see figure] Key idea: S_N1 rate depends on carbocation stability. 1-Bromoe... 1
- Which one of the following alcohols reacts instantaneously with Lucas reagent? Answer: 1. CH₃-C(CH₃)(CH₃)-OH (i.e. (CH₃)₃C-OH , drawn with CH₃ above and below the carbon) Key idea: Lucas reagent ( ZnCl₂ /conc. HCl) work... 1
- Major products A and B formed in the following reaction sequence, are[scheme: 2-methylcyclohexanol (OH and H_3C on adjacent ring carbons) PBr_3 A (major) [Δ]alc.\ KOH B (major), see figure] Answer: 2. A = [structure: 1-bromo-2-methylcyclohexane], B = [structure: 1-methylcyclohexene (double bond adjacent to methyl carbon)] Key id... 1
- Match List I with List II.List I (Reactions): A. [structure: bicyclohexylidene → 2 cyclohexanone] B. [structure: benzene → benzophenone] C. [structure: cyclohexanol → cyclohexanone] D. [structure: ethylbenzene → potassium benzoate]List II (Reagents/C… Answer: 4. A-IV, B-I, C-II, D-III Key idea: identify the reagent for each conversion. A: alkene to two ketones is ozonolysis, O₃ , then Zn-H... 1
- Given below are two statements:Statement I : The boiling point of hydrides of Group 16 elements follow the orderH_2O > H_2Te > H_2Se > H_2S.Statement II : On the basis of molecular mass, H_2O is expected to have lower boiling point than the other mem… Answer: 2. Both Statement I and Statement II are true. Key idea: boiling point of hydrides depends on H-bonding and on molecular mass. H₂O i... 1
- On heating, some solid substances change from solid to vapour state without passing through liquid state. The technique used for the purification of such solid substances based on the above principle is known as Answer: 3. Sublimation Key idea: sublimation is the conversion of solid directly into vapour. Solids like camphor, naphthalene and iodine ar... 1
- Match List I with List II.List I (Conversion): A. 1 mol of H_2O to O_2 B. 1 mol of MnO_4^- to Mn^2+ C. 1.5 mol of Ca from molten CaCl_2 D. 1 mol of FeO to Fe_2O_3List II (Number of Faraday required): I. 3F II. 2F III. 1F IV. 5FChoose the correct answ… Answer: 2. A-II, B-IV, C-I, D-III Key idea: Faradays = moles of electrons transferred. A: 2H₂O→ O₂+4H^++4e^- , so 1 mol H₂O needs 2 F (II).... 1
- Which reaction is NOT a redox reaction? Answer: 1. BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl Key idea: a redox reaction has a change in oxidation numbers. BaCl₂+Na₂SO₄→ BaSO₄+2NaCl is a doubl... 1
- The highest number of helium atoms is in Answer: 2. 4 mol of helium Key idea: convert each to number of atoms (He is monoatomic). 2.271098 L at STP (22.7 L/mol): 0.1 mol. 4 mol: 4 m... 1
- 1 gram of sodium hydroxide was treated with 25 mL of 0.75 M HCl solution, the mass of sodium hydroxide left unreacted is equal to Answer: 3. 250 mg Key idea: find the limiting reagent for NaOH+HCl→ NaCl+H₂O . NaOH: 1/40=0.025 mol = 25 mmol. HCl: 25×0.75=18.75 mmol. Left... 1
- The most stable carbocation among the following is: Answer: 1. [structure: methylcyclohexyl carbocation, see figure] Key idea: carbocation stability: tertiary > secondary > primary, and more h... 1
- A compound with a molecular formula of C_6H_14 has two tertiary carbons. Its IUPAC name is: Answer: 4. 2,3-dimethylbutane Key idea: a tertiary carbon is bonded to three other carbons (one C-H). 2,2-dimethylbutane: one quaternary C,... 1
- Match List I with List II.List I (Quantum Number): A. m_l B. m_s C. l D. nList II (Information provided): I. shape of orbital II. size of orbital III. orientation of orbital IV. orientation of spin of electronChoose the correct answer from the option… Answer: 3. A-III, B-IV, C-I, D-II Key idea: each quantum number gives one property of the electron or orbital. m_l : orientation of the orbi... 1
- The reagents with which glucose does not react to give the corresponding tests/products areA. Tollen's reagent B. Schiff's reagent C. HCN D. NH_2OH E. NaHSO_3Choose the correct options from the given below: Answer: 4. B and E Key idea: glucose exists mostly as the cyclic hemiacetal, so it gives some but not all aldehyde reactions. Tollens' reage... 1
- Match List I with List II.List I (Molecule): A. ethane B. ethene C. carbon molecule, C_2 D. ethyneList II (Number and types of bond/s between two carbon atoms): I. one σ-bond and two π-bonds II. two π-bonds III. one σ-bond IV. one σ-bond and one π-bo… Answer: 4. A-III, B-IV, C-II, D-I Key idea: count the bond between the two carbons. Ethane H₃C-CH₃ : one σ bond (III). Ethene: one σ + one π... 1
- Match List I with List II.List I (Compound): A. NH_3 B. BrF_5 C. XeF_4 D. SF_6List II (Shape/geometry): I. Trigonal Pyramidal II. Square Planar III. Octahedral IV. Square PyramidalChoose the correct answer from the options given below: Answer: 2. A-I, B-IV, C-II, D-III Key idea: use VSEPR to get the shape of each molecule. NH₃ : 3 bond pairs + 1 lone pair gives trigonal pyr... 1
- Match List I with List II.List I (Process): A. Isothermal process B. Isochoric process C. Isobaric process D. Adiabatic processList II (Conditions): I. No heat exchange II. Carried out at constant temperature III. Carried out at constant volume IV. C… Answer: 1. A-II, B-III, C-IV, D-I Key idea: the prefix tells the fixed quantity. Isothermal: constant temperature (II). Isochoric: constant... 1
- Arrange the following elements in increasing order of first ionization enthalpy:Li, Be, B, C, NChoose the correct answer from the options given below: Answer: 3. Li < B < Be < C < N Key idea: ionization enthalpy increases across a period, with exceptions at Be (filled 2s) and N (half-filled... 1
- For the reaction 2A ⇌ B + C, K_c = 4×10^-3. At a given time, the composition of reaction mixture is : [A]=[B]=[C]=2×10^-3 M.Then, which of the following is correct? Answer: 4. Reaction has a tendency to go in backward direction. Key idea: compare the reaction quotient Q_c with K_c . Q_c=[B][C]/[A]²=frac(... 1
- In which of the following equilibria, K_p and K_c are NOT equal? Answer: 2. PCl_(5(g)) ⇌ PCl_(3(g)) + Cl_(2(g)) Key idea: K_p=K_c(RT)^(Δ n_g) . They are equal only when Δ n_g=0 . 2BrCl⇌ Br₂+Cl₂ : Δ n_g=0 .... 1
- Given below are two statements:Statement I : Aniline does not undergo Friedel-Crafts alkylation reaction.Statement II : Aniline cannot be prepared through Gabriel synthesis.In the light of the above statements, choose the correct answer from the opti… Answer: 2. Both Statement I and Statement II are true. Key idea: the -NH₂ group of aniline is basic and reacts with Lewis acids; Gabriel syn... 1
- Identify the correct reagents that would bring about the following transformation.[structure transformation shown in figure: ring-CH_2-CH=CH_2 → ring-CH_2-CH_2-CHO] Answer: 3. (i) BH₃ (ii) H₂O₂/oversetominusOH (iii) PCC Key idea: the -CH=CH₂ group must become -CH₂CH₂CHO , a terminal aldehyde, which needs... 1
- Among Group 16 elements, which one does NOT show -2 oxidation state? Answer: 1. Po Key idea: metallic character increases down the group, so the -2 state becomes unfavourable. O, S, Se and Te form oxides, sulp... 1
- The equilibrium concentrations of the species in the reaction A + B ⇌ C + D are 2, 3, 10 and 6 mol L^-1, respectively at 300 K. Δ G^° for the reaction is (R = 2 cal / mol K) Answer: 4. -1381.80 cal Key idea: Δ G^° = -2.303 RTlog K . K = [C][D]/[A][B] = 10 × 6/2 × 3 = 10 , so log K = 1 . Δ G^° = -2.303 × 2 × 300 ×... 1