Chemistry
- Predict the correct order among the following : Answer: 1. lone pair - lone pair > lone pair - bond pair > bond pair - bond pair Key idea (VSEPR): a lone pair is held only by one nucleus,... 1
- The addition of a catalyst during a chemical reaction alters which of the following quantities ? Answer: 4. Activation energy Key idea: a catalyst provides a different path with a lower activation energy. It does not change the state fun... 1
- Consider the following liquid - vapour equilibrium.Liquid ⇌ VapourWhich of the following relations is correct ? Answer: 4. dln P/dT = Δ H_v/RT² Key idea: this is the Clausius-Clapeyron equation for liquid-vapour equilibrium: dln P/dT=Δ H_v/RT² Vapour p... 1
- The correct thermodynamic conditions for the spontaneous reaction at all temperatures is : Answer: 3. Δ H < 0 and Δ S > 0 Key idea: Δ G=Δ H-TΔ S . A reaction is spontaneous at all temperatures when Δ G<0 for every T. This needs Δ H... 1
- Which of the following has longest C-O bond length ? (Free C-O bond length in CO is 1.128\ .) Answer: 3. [Fe(CO)₄]²⁻ Key idea: in metal carbonyls, back bonding from metal d orbitals into the CO π^* orbital weakens the C-O bond and len... 1
- Which one of the following statements is correct when SO_2 is passed through acidified K_2Cr_2O_7 solution ? Answer: 4. Green Cr₂(SO₄)₃ is formed. Key idea: SO₂ is a reducing agent and acidified dichromate is an oxidising agent. mathrmCr₂O₇²⁻+3SO₂+2... 1
- The electronic configurations of Eu (Atomic No. 63), Gd (Atomic No. 64) and Tb (Atomic No. 65) are : Answer: 4. [Xe]4f⁷6s² , [Xe]4f⁷5d¹6s² and [Xe]4f⁹6s² Key idea: half-filled 4f⁷ is extra stable, and Gd and Tb follow from it. Eu (63): [Xe]4... 1
- Match items of Column I with the items of Column II and assign the correct code :Column I: (a) Cyanide process; (b) Froth floatation process; (c) Electrolytic reduction; (d) Zone refiningColumn II: (i) Ultrapure Ge; (ii) Dressing of ZnS; (iii) Extrac… Answer: 1. (iv) (ii) (iii) (i) Key idea: match each process with its use. (a) Cyanide process: extraction of gold (Au), iv. (b) Froth floata... 1
- The correct statement regarding the comparison of staggered and eclipsed conformations of ethane, is : Answer: 4. The staggered conformation of ethane is more stable than eclipsed conformation, because staggered conformation has no torsional s... 1
- Consider the nitration of benzene using mixed conc. H_2SO_4 and HNO_3. If a large amount of KHSO_4 is added to the mixture, the rate of nitration will be : Answer: 2. slower Key idea: nitration needs the nitronium ion, formed by HNO₃+2H₂SO₄⇌ NO₂^++H₃O^++2HSO₄^- KHSO₄ adds a large amount of HSO₄^... 1
- Which of the following reagents would distinguish cis-cyclopenta-1, 2-diol from the trans-isomer ? Answer: 1. Acetone Key idea: only the cis-1,2-diol has both -OH groups on the same side of the ring, so it can form a cyclic five-membered k... 1
- The product formed by the reaction of an aldehyde with a primary amine is : Answer: 1. Schiff base Key idea: an aldehyde (or ketone) condenses with a primary amine with loss of water to give an imine, R-CH=N-R' , als... 1
- The reaction[cyclopentanol, then NaH giving sodium cyclopentoxide, then Me-I giving methyl cyclopentyl ether; scheme shown in figure]can be classified as : Answer: 1. Williamson ether synthesis reaction Key idea: an alcohol is converted by a strong base (NaH) into an alkoxide, which then attacks... 1
- When copper is heated with conc. HNO_3 it produces : Answer: 1. Cu(NO₃)₂ and NO₂ Key idea: the reduction product of nitric acid depends on its concentration. Cu+4HNO₃(conc.)→ Cu(NO₃)₂+2NO₂+2H₂O... 1
- The product obtained as a result of a reaction of nitrogen with CaC_2 is : Answer: 1. Ca(CN)₂ Key idea: calcium carbide absorbs nitrogen at high temperature to give calcium cyanamide (nitrolim) and carbon. CaC₂+N₂→... 1
- Which is the correct statement for the given acids ? Answer: 2. Phosphinic acid is a monoprotic acid while phosphonic acid is a diprotic acid. Key idea: only the P-OH hydrogens are acidic. Phos... 1
- Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules ? Answer: 2. Cl₂ > Br₂ > F₂ > I₂ Key idea: bond dissociation enthalpy generally falls down group 17 (bigger atoms, longer bonds), but F₂ is un... 1
- Fog is a colloidal solution of : Answer: 1. Liquid in gas Key idea: fog consists of tiny water droplets (liquid) dispersed in air (gas), so it is a colloid of liquid in gas,... 1
- The pressure of H_2 required to make the potential of H_2 - electrode zero in pure water at 298 K is : Answer: 1. 10⁻¹⁴ atm Key idea: for the half cell 2H^++2e^-→ H₂ , the Nernst equation is E=0-0.059/2logfracP_(H_2)[H^+]² In pure water [H^+]=... 1
- Which of the following statements about the composition of the vapour over an ideal 1 : 1 molar mixture of benzene and toluene is correct ? Assume that the temperature is constant at 25°C. (Given, Vapour Pressure Data at 25°C, benzene = 12.8 kPa, tol… Answer: 1. The vapour will contain a higher percentage of benzene. Key idea: the component with the higher vapour pressure is more volatile... 1
- Lithium has a bcc structure. Its density is 530\ kg\ m^-3 and its atomic mass is 6.94\ g\ mol^-1. Calculate the edge length of a unit cell of Lithium metal. (N_A = 6.02×10^23\ mol^-1) Answer: 2. 352 pm Key idea: ρ=Z M/N_A a³ , with Z = 2 for bcc. ρ=530\ mathrmkg m⁻³=0.530\ mathrmg cm⁻³ . a³=frac2×6.946.02×10²³×0.530=4.35×1... 1
- Equal moles of hydrogen and oxygen gases are placed in a container with a pin-hole through which both can escape. What fraction of the oxygen escapes in the time required for one-half of the hydrogen to escape ? Answer: 1. 1/8 Key idea: Graham's law, rate of effusion ∝ 1/√(M) . fracr_(H_2)r_(O_2)=√(32/2)=4 Both gases start with equal moles and leave... 1
- Natural rubber has : Answer: 1. All cis-configuration Key idea: natural rubber is cis-1,4-polyisoprene. All the double bonds in the chain have cis configuration,... 1
- Which of the following is an analgesic ? Answer: 1. Novalgin Key idea: an analgesic relieves pain. Novalgin is an analgesic (and antipyretic). Penicillin, streptomycin and chloromyc... 1