CBSE Class 12 Chemistry 2024 — Set 56/2/1

An azeotropic solution of two liquids has boiling point lower than either of them when it : (A) is saturated (B) shows positive deviation from Raoult's law (C) shows negative deviation from Raoult's law (D) shows no deviation from Raoult's law

The relative lowering of vapour pressure of an aqueous solution containing non-volatile solute is 0·0225. The mole fraction of the non-volatile solute is : (A) 0·80 (B) 0·725 (C) 0·15 (D) 0·0225

During electrolysis of aqueous solution of NaCl : (A) H₂ (g) is liberated at cathode (B) Na is formed at cathode (C) O₂ (g) is liberated at anode (D) Cl₂ (g) is liberated at cathode

The addition of catalyst during a chemical reaction alters which of the following quantities of the reaction ? (A) Enthalpy (B) Activation energy (C) Entropy (D) Internal energy

For the elementary reaction P arrow Q, the rate of disappearance of 'P' increases by a factor of 8 on doubling the concentration of 'P'. The order of the reaction with respect to 'P' is : (A) 3 (B) 4 (C) 2 (D) 1

Assertion (A) : Aliphatic primary amines can be prepared by Gabriel phthalimide synthesis. Reason (R) : Alkyl halides undergo nucleophilic substitution with anion formed by phthalimide. Select the correct answer from the codes given below : (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A) : Uracil base is present in DNA. Reason (R) : DNA undergoes self-replication. Select the correct answer from the codes given below : (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A) : Diazonium salts of aromatic amines are more stable than those of aliphatic amines. Reason (R) : Diazonium salts of aliphatic amines show resonance. Select the correct answer from the codes given below : (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A) : p-nitroaniline is a weaker base than p-toluidine. Reason (R) : The electron withdrawing effect of -NO₂ group in p-nitroaniline makes it a weaker base. Select the correct answer from the codes given below : (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

A 6% solution of glucose (molar mass = 180 g mol⁻¹) is isotonic with 2·5% solution of an unknown organic substance. Calculate the molecular weight of the unknown organic substance.

A first order reaction has a rate constant 1·25 × 10⁻³ s⁻¹. How long will 5 g of this reactant take to reduce to 2·5 g ? [ log 2 = 0·301, log 3 = 0·4771, log 4 = 0·6021 ]

(a) What is lanthanoid contraction ? Actinoid contraction is greater from element to element than lanthanoid contraction. Why ? OR (b) Why do transition metals have high enthalpy of atomization ? Which element of 3d-series has lowest enthalpy of atomization ?

(a) In the following pair of compounds, which compound undergoes SN2 reaction faster and why ? 1-iodopropane (CH₃CH₂CH₂I) OR 1-bromopropane (CH₃CH₂CH₂Br) (b) Write the major product in the following : Ethylbenzene (C₆H₅CH₂CH₃) xrightarrowCl₂, UVlight

Define the following terms : (a) Denaturation of protein (b) Invert sugar

Write the structures of A, B and C in the following reactions : (a) CH₃-CH₂-Br xrightarrowKCN A xrightarrow[hydrolysis]Partial B xrightarrowNaOH + Br₂ C (b) C₆H₅NO₂ xrightarrowFe/HCl A xrightarrowNaNO₂/HCl B xrightarrowC₂H₅OH C

Write the reaction involved in the following : (a) Wolff-Kishner reduction (b) Decarboxylation reaction (c) Cannizzaro reaction

Give the equations of reactions for the preparation of : (any three) (a) Phenol from chlorobenzene (b) Salicylaldehyde from phenol (c) 2-Methoxyacetophenone from anisole (d) Picric acid from phenol

Give reasons for the following : (a) Chlorine is ortho/para directing in electrophilic aromatic substitution reactions, though chlorine is an electron withdrawing group. (b) Racemic mixture is optically inactive. (c) Allyl chloride is hydrolysed more readily than n-propyl chloride.

The vapour pressure of a solvent at 283 K is 100 mm Hg. Calculate the vapour pressure of a dilute solution containing 1 mole of a strong electrolyte AB in 50 moles of the solvent at 283 K (assuming complete dissociation of solute AB).

Calculate emf of the following cell : Zn(s)|Zn²⁺(0·1M)||Sn²⁺(0·001M)|Sn(s) Given : E^°Zn²⁺/Zn = -0·76 V, E^°Sn²⁺/Sn = -0·14 V [ log 10 = 1 ]

The rate of a gaseous reaction triples when temperature is increased from 17ºC to 27ºC. Calculate the energy of activation for this reaction. [ Given : 2·303 R = 19·15 JK⁻¹ mol⁻¹, log 3 = 0·48 ]

Carbohydrates are essential for life in both plants and animals. Carbohydrates are used as storage molecules as starch in plants and glycogen in animals. Chemically they are polyhydroxy aldehydes or ketones. On the basis of their behaviour on hydrolysis, carbohydrates are classified as monosaccharides, oligosaccharides and polysaccharides. All monosaccharides are reducing sugars. A monosaccharide like glucose is aldohexose and its molecular formula was found to be C₆H₁₂O₆. After reacting with different reagents like HI, H₂N-OH, Bromine water, (CH₃CO)₂O, etc. its structure was found to contain one aldehyde group, one primary alcoholic group (-CH₂OH) and four secondary alcoholic groups (-CHOH). Despite having the aldehyde group, glucose does not give some of the reactions of aldehyde group like Schiff's test, NaHSO₃ addition. This explains the existence of glucose in two cyclic hemiacetal forms which differ only in the configuration of the hydroxyl group at C-1. Answer the following questions : (a) What are reducing sugars ? (b) Classify the following into monosaccharide and disaccharide : Fructose, Sucrose, Lactose, Galactose (c) Name that polysaccharide which is called animal starch. Why is it called animal starch ? OR (c) (i) Name the isomers of glucose which in the cyclic form differ only in the configuration of the -OH group at C-1. (ii) Presence of which functional group was detected when glucose reacted with Br₂ water ?

Transition metals have incomplete d-subshell either in neutral atom or in their ions. The presence of partly filled d-orbitals in their atoms makes transition elements different from that of the non-transition elements. With partly filled d-orbitals, these elements exhibit certain characteristic properties such as display of a variety of oxidation states, formation of coloured ions and entering into complex formation with a variety of ligands. The transition metals and their compounds also exhibit catalytic properties and paramagnetic behaviour. The transition metals are very hard and have low volatility. An examination of the E^°(M²⁺/M) values shows the varying trends : E^°(M²⁺/M)/V : V -1·18, Cr -0·91, Mn -1·18, Fe -0·44, Co -0·28, Ni -0·25, Cu +0·34, Zn -0·76 Answer the following questions : (a) On what basis can we say that Cu is a transition element but Zn is not ? (Atomic number : Cu = 29, Zn = 30) (b) Why do transition elements show variety of oxidation states ? (c) (i) Why do E^°(M²⁺/M) values show irregular trend from Vanadium to Zinc ? (ii) How is the variability in oxidation states of transition metals different from that of the non-transition elements ? OR (c) (i) Of the d⁴ species, Cr²⁺ is strongly reducing while Mn³⁺ is strongly oxidizing. Why ? (Atomic number : Cr = 24, Mn = 25) (ii) Complete the following ionic equation : MnO₄^- + H₂O + I^- arrow

Answer any five of the following : (a) How is the crystal field splitting energy for octahedral complex (Δo) related to that of tetrahedral complex (Δt) ? (b) Write the IUPAC name of the following complex : [PtCl₂(en)₂](NO₃)₂ (c) Write the geometry and magnetic behaviour of the complex [Ni(CO)₄] on the basis of Valency Bond Theory (VBT). (d) What type of isomerism is shown by the complex [Co(NH₃)₆][Cr(CN)₆] ? (e) For the coordination compound on the basis of crystal field theory, write the electronic configuration for d⁴ ion if Δo < P. Is the coordination compound a high spin or low spin complex ? (f) Out of [Co(NH₃)₆]³⁺ and [Co(NH₃)₄Cl₂]^+, which complex is heteroleptic and why ? (g) Draw the structures of optical isomers of [PtCl₂(en)₂]²⁺.

(a) (i) Account for the following : (1) Oxidation of aldehydes is easier as compared to ketones. (2) The alpha (α) hydrogen atoms of aldehydes are acidic in nature. (ii) Write the products in the following reactions : (1) Acetophenone, C₆H₅COCH₃ xrightarrowNaOH/I₂ ? (2) Benzoyl chloride, C₆H₅COCl + (CH₃)₂Cd arrow ? + CdCl₂ (iii) Give a simple chemical test to distinguish between ethanoic acid and ethanal. **OR** (b) (i) Draw structure of the 2,4-dinitrophenylhydrazone of benzaldehyde. (ii) Arrange the following in increasing order of their reactivity towards HCN : Acetone, CH₃COCH₃, 3,3-dimethylbutan-2-one, (CH₃)₃C-COCH₃, Ethanal, CH₃CHO (iii) How can you convert phenyl magnesium bromide to benzoic acid ? (iv) Give a simple chemical test to distinguish between benzaldehyde and ethanal. (v) Write the main product in the following reaction : Ethyl 3-oxobutanoate, CH₃COCH₂COOC₂H₅ xrightarrow[(ii)H^+](i)NaBH₄ ?

(a) (i) The resistance of 0·05 M CH₃COOH solution is found to be 100 ohm. If the cell constant is 0·0354 cm⁻¹, calculate the molar conductivity of the acetic acid solution. (ii) Write Faraday's first law of electrolysis. How many Faraday is required for the reduction of 1 mol of MnO₄^- to Mn²⁺ ? OR (b) (i) The conductivity of 0·0025 mol L⁻¹ acetic acid is 5·25 × 10⁻⁵ S cm⁻¹. Calculate its degree of dissociation if Lambda^°m for acetic acid is 390 S cm² mol⁻¹. (ii) Write anode, cathode and overall reaction of lead storage battery.