Chemistry

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The species, having bond angles of 120° is : Answer: 3. BCl₃ Key idea: 120^° belongs to a trigonal planar molecule with no lone pair on the central atom. BCl₃ : B has 3 bond pairs, sp²... VSEPR theory and shapes of molecules 1 answer
Which of the following pairs of compounds is isoelectronic and isostructural ? Answer: 2. IBr₂^-, XeF₂ Key idea: isoelectronic means equal number of valence electrons, isostructural means same shape. XeF₂ : 8 + 14 = 22... VSEPR theory and shapes of molecules 1 answer
A first order reaction has a specific reaction rate of 10^-2\ sec^-1. How much time will it take for 20 g of the reactant to reduce to 5 g ? Answer: 1. 138.6 sec Key idea: first-order integrated rate law t=2.303/kloga/a-x . t=dfrac2.30310⁻²log20/5=230.3×0.602=138.6\ s . Check: 20... Integrated rate equations and half-life (zero and first order) 1 answer
A gas is allowed to expand in a well insulated container against a constant external pressure of 2.5 atm from an initial volume of 2.50 L to a final volume of 4.50 L. The change in internal energy Δ U of the gas in joules will be : Answer: 2. -505 J Key idea: well insulated means adiabatic, so q = 0 and Δ U = w . w=-p_extΔ V=-2.5\ atm×(4.50-2.50)\ L=-5\ L atm . Taking 1... First law: work, heat, internal energy, enthalpy 1 answer
Correct increasing order for the wavelengths of absorption in the visible region for the complexes of Co^3+ is : Answer: 4. [Co(en)₃]³⁺, [Co(NH₃)₆]³⁺, [Co(H₂O)₆]³⁺ Key idea: stronger ligand field means a larger splitting Δ_o , which means light of highe... Crystal field theory, colour and magnetic properties 1 answer
The correct order of the stoichiometries of AgCl formed when AgNO_3 in excess is treated with the complexes : CoCl_3.6NH_3, CoCl_3.5NH_3, CoCl_3.4NH_3 respectively is : Answer: 2. 3 AgCl, 2 AgCl, 1 AgCl Key idea: only ionisable (outside the coordination sphere) chloride precipitates with AgNO₃ . CoCl₃·6NH₃ =... Werner's theory, ligands, coordination number, denticity, chelation 1 answer
The reason for greater range of oxidation states in actinoids is attributed to : Answer: 2. 5f, 6d and 7s levels having comparable energies Key idea: a wide range of oxidation states needs electrons from orbitals of simil... Actinoids 1 answer
Extraction of gold and silver involves leaching with CN^- ion. Silver is later recovered by : Answer: 3. displacement with Zn Key idea: Ag is recovered from the cyanide complex by a more electropositive metal. 2[Ag(CN)₂]^- + Zn → [Zn(... Transition elements: configuration, occurrence and characteristics 1 answer
Concentration of the Ag^+ ions in a saturated solution of Ag_2C_2O_4 is 2.2 × 10^-4 mol L^-1. Solubility product of Ag_2C_2O_4 is : Answer: 3. 5.3 × 10⁻¹² Key idea: Ag₂C₂O₄ ⇌ 2Ag^+ + C₂O₄²⁻ , K_sp=[Ag^+]²[C₂O₄²⁻] . [C₂O₄²⁻]=1/2[Ag^+]=1.1×10⁻⁴ M. K_sp=(2.2×10⁻⁴)²×1.1×10⁻⁴=... Solubility product 1 answer
Predict the correct intermediate and product in the following reaction :H_3C-C CH [HgSO_4]H_2O,\ H_2SO_4 intermediate (A) → product (B) Answer: 3. A : H₃C-C(OH)=CH₂ B : H₃C-C(=O)-CH₃ Key idea: hydration of an alkyne (Kucherov reaction) first gives an enol, which tautomerises... Alkynes: acidic character and addition reactions 1 answer
Which one is the correct order of acidity ? Answer: 1. CHequiv CH > CH₃-Cequiv CH > CH₂=CH₂ > CH₃-CH₃ Key idea: acidity of a C-H bond increases with the s-character of carbon. Ethyne (... Alkynes: acidic character and addition reactions 1 answer
Which of the following reactions is appropriate for converting acetamide to methanamine ? Answer: 1. Hoffmann hypobromamide reaction Key idea: Hoffmann bromamide reaction removes one carbon from an amide to give a primary amine. C... Amines: nomenclature, classification, structure, preparation 1 answer
Consider the reactions :X\ (C_2H_6O) Cu/573\ K A [Ag(NH_3)_2]^+,\ ^-OH,Δ Silver mirror observed; A ^-OH,Δ Y; A NH_2-NH-C(=O)-NH_2 ZIdentify A, X, Y and Z Answer: 2. A-Ethanal, X-Ethanol, Y-But-2-enal, Z-Semicarbazone. Key idea: C₂H₆O with Cu/573 K dehydrogenation means a primary alcohol. X = e... Alcohols: identification of 1/2/3 alcohols, dehydration mechanism 1 answer
Of the following, which is the product formed when cyclohexanone undergoes aldol condensation followed by heating ? Answer: 1. [structure: 2-cyclohexylidenecyclohexanone] Key idea: aldol condensation = aldol addition followed by loss of water on heating, g... Alpha-hydrogen acidity, aldol, Cannizzaro, haloform 1 answer
The heating of phenyl-methyl ethers with HI produces. Answer: 2. phenol Key idea: HI cleaves an aryl alkyl ether at the alkyl-oxygen bond. C₆H₅OCH₃ + HI → C₆H₅OH + CH₃I . The oxygen is protonate... Ethers 1 answer
Which one is the most acidic compound ? Answer: 3. [structure: 2,4,6-trinitrophenol] Key idea: electron-withdrawing groups stabilise the phenoxide ion and increase acidity. 2,4,6-T... Phenols: acidity, electrophilic substitution, Reimer-Tiemann 1 answer
In which pair of ions both the species contain S-S bond ? Answer: 1. S₄O₆²⁻, S₂O₃²⁻ Key idea: draw the structures. mathrmS₄O₆²⁻ (tetrathionate): has an S-S bond in the chain O₃S-S-S-SO₃ . mathrmS₂O₃... General trends, Group 15 and 16 1 answer
Match the interhalogen compounds of column I with the geometry in column II and assign the correct code.Column I | Column II(a) XX' | (i) T-shape(b) XX_3' | (ii) Pentagonal bipyramidal(c) XX_5' | (iii) Linear(d) XX_7' | (iv) Square-pyramidal| (v) Tet… Answer: 1. (iii) (i) (iv) (ii) Key idea: use VSEPR for interhalogens. (a) XX': linear (iii) (b) XX₃' : T-shape (i) (3 bond pairs, 2 lone pai... General trends, Group 17 and 18 1 answer
The most suitable method of separation of 1 : 1 mixture of ortho and para-nitrophenols is : Answer: 3. Steam distillation Key idea: o-nitrophenol is steam volatile, p-nitrophenol is not. o-Nitrophenol has intramolecular hydrogen bon... Purification: crystallization, sublimation, distillation, differential extraction 1 answer
Ionic mobility of which of the following alkali metal ions is lowest when aqueous solution of their salts are put under an electric field ? Answer: 3. Li Key idea: in aqueous solution ionic mobility falls with greater hydration, and smaller ions hydrate more. Hydrated size order... Conductance, molar conductivity and its variation with concentration 1 answer
In the electrochemical cell :Zn|ZnSO_4(0.01\ M)||CuSO_4(1.0\ M)|Cu, the emf of this Daniel cell is E_1. When the concentration of ZnSO_4 is changed to 1.0 M and that of CuSO_4 changed to 0.01 M, the emf changes to E_2. From the followings, which one… Answer: 2. E₁ > E₂ Key idea: apply the Nernst equation, E = E^° - 0.059/2logdfrac[Zn²⁺][Cu²⁺] . E₁ : log0.01/1=-2 , so E₁ = E^° + 0.059 . E₂... EMF, Nernst equation and applications 1 answer
If molality of the dilute solution is doubled, the value of molal depression constant (K_f) will be : Answer: 3. unchanged Key idea: K_f is a property of the solvent only. Δ T_f = K_f m . K_f is the depression for a 1 molal solution and depen... Colligative properties 1 answer
The correct statement regarding electrophile is : Answer: 3. Electrophile can be either neutral or positively charged species and can form a bond by accepting a pair of electrons from a nucl... Electrophiles and nucleophiles 1 answer
The IUPAC name of the compound OHC-CH(CH_3)-C(=O)-CH=CH-CH_3 (drawn in skeletal form) is ______. Answer: 4. 3-keto-2-methylhex-4-enal Key idea: the principal functional group is the aldehyde (-CHO), which gets C-1. Chain: OHC(1)-CH(CH₃)(... Nomenclature (trivial and IUPAC) 1 answer

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