CBSE Class 12 Chemistry 2025 — Set 56/6/1

Which one of the following amines gives an alcohol on reaction with HNO₂ ? (A) C₆H₅NH₂ (aniline) (B) C₂H₅NH₂ (C) (C₂H₅)₂NH (D) (C₂H₅)₃N

The freezing point of one molal KCl solution, assuming KCl to be completely dissociated in water, is : (Kf for water = 1·86 K kg mol⁻¹) (A) -3·72°C (B) +3·72°C (C) -1·86°C (D) +2·72°C

A solution of acetone in ethanol : (A) obeys Raoult's law. (B) forms an ideal solution. (C) shows a positive deviation from Raoult's law. (D) shows a negative deviation from Raoult's law.

Which of the following cell converts the energy of combustion of fuel into electrical energy ? (A) Mercury cell (B) Fuel cell (C) Dry cell (D) Lead storage cell

The unit of rate and rate constant are same for a : (A) First order reaction (B) Second order reaction (C) Zero order reaction (D) Third order reaction

Pyranose ring of glucose is formed due to the reaction between : (A) C₁ and C₃ (B) C₁ and C₅ (C) C₁ and C₄ (D) C₁ and C₂

For the following question, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as 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) : Actinoids show wide range of oxidation states. Reason (R) : Actinoids are radioactive in nature.

For the following question, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as 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) : Hydrolysis of an ester follows first order kinetics. Reason (R) : The concentration of water does not get altered much during the reaction.

For the following question, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as 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) : Boiling point of (CH₃)₃N is higher than that of CH₃CH₂CH₂NH₂. Reason (R) : Hydrogen bonding is more extensive in CH₃CH₂CH₂NH₂.

For the following question, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as 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) : Phenol is strongly acidic as compared to ethanol. Reason (R) : Phenoxide ion is more stable than ethoxide ion.

State Henry's law. Why are aquatic species more comfortable in cold water as compared to warm water ?

Observe the graph in the given figure and answer the following questions : (Drawn graph: log [R]₀/[R] on the y-axis against Time on the x-axis — a straight line rising from the origin.) (a) Predict the order of reaction. (b) What is the slope of the curve ?

(a) Write IUPAC names of the following coordination compounds : (i) [CoCl₂(en)₂]SO₄ (ii) K₃[Fe(C₂O₄)₃] OR (b) Differentiate between : (i) Double salt and Complex compound (ii) Didentate ligand and Ambidentate ligand

Draw the structures of major monohalo products in each of the following reactions : (a) 1-Methylcyclohexene (C₇H₁₂, drawn: cyclohexene ring with a CH₃ group on a double-bond carbon) + HI longrightarrow ? (b) Cyclohexene (C₆H₁₀, drawn ring with one C=C) + Br₂ xrightarrowHeat or UV light ?

How do you explain the following ? (a) Presence of an aldehydic group in glucose. (b) Presence of five – OH groups in glucose.

Vapour pressure of pure water at 298 K is 24·8 mm Hg. Calculate the lowering in vapour pressure of an aqueous solution which freezes at -0·3°C. (Kf of water = 1·86 K kg mol⁻¹)

The rate of a reaction : A + B longrightarrow product is given below as a function of different initial concentrations of A and B. | Experiment | [A]/mol L⁻¹ | [B]/mol L⁻¹ | Initial Rate/mol L⁻¹ min⁻¹ | | --- | --- | --- | --- | | 1 | 0·01 | 0·01 | 5 × 10⁻³ | | 2 | 0·02 | 0·01 | 1 × 10⁻² | | 3 | 0·01 | 0·02 | 5 × 10⁻³ | Calculate the order of the reaction with respect to A and B. Determine the rate constant of the reaction.

Give reasons for the following : (a) The pH of aqueous NaCl increases when it is electrolysed. (b) Unlike dry cell, mercury cell has a constant cell potential through its lifetime. (c) Conductivity of solution decreases with dilution.

(a) Answer the following about the complexes [FeF₆]³⁻ and [Fe(CN)₆]⁴⁻ : (i) Write the hybridization involved in each case. (ii) Which of them is the outer orbital complex and which one is the inner orbital complex ? (iii) Compare their magnetic behaviour. [Atomic number : Fe = 26] OR (b) (i) What happens to the colour of complex [Ti(H₂O)₆]³⁺ when heated gradually ? (ii) Write the electronic configuration for d⁵ ion if Δo < P. (iii) Write the hybridization and magnetic behaviour of the complex [Ni(CO)₄]. [Atomic number : Ni = 28]

Write any two differences between SN1 and SN2 reactions. Which of the following compounds would undergo SN1 reaction faster and why ? (Cyclohexylmethyl chloride) C₆H₁₁-CH₂-Cl (drawn: cyclohexane ring bearing -CH₂-Cl) or (Benzyl chloride) C₆H₅-CH₂-Cl (drawn: benzene ring bearing -CH₂-Cl)

A compound (A) with molecular formula C₄H₅N on reduction with DIBAL-H followed by hydrolysis, gives a compound (B). Compound (B) gives positive Tollens' test but does not give iodoform test. Compound (B) can also be obtained when ethanal is treated with dilute NaOH followed by heating. Identify (A) and (B). Write the reactions of (A) with DIBAL-H followed by hydrolysis.

How will you obtain the following from aniline ? Give chemical equations only. (a) Sulphanilic acid (b) Phenylisocyanide (c) Acetanilide

Read the case carefully and answer the questions that follow. Alcohols undergo a number of reactions involving the cleavage of C – OH bond. However, phenols do not undergo reactions involving the cleavage of C – OH bond. Alcohols are weaker acids than water. Alcohols react with halogen acids to form the corresponding haloalkanes. Phenols are stronger acids than alcohols. A characteristic feature of phenols is that they undergo electrophilic substitution reactions such as halogenation, nitration, etc. Since – OH group is a strong activating group, phenol gives trisubstituted products during halogenation, nitration, etc. (a) What happens when phenol is treated with the following ? (i) Br₂ water (ii) Conc. HNO₃ (b) (i) Write the mechanism of alcohol reacting as nucleophile in a reaction with CH₃oplus (methyl cation). OR (b) (ii) Why do phenols not undergo reactions involving cleavage of C – OH bond ? (c) How can you distinguish between Butan-1-ol and 2-Methylpropan-2-ol by using HCl in the presence of anhydrous ZnCl₂ ?

Read the case carefully and answer the questions that follow. The α-amino acids are the building blocks of proteins. All α-amino acids exist as zwitter ion due to which they show amphoteric behaviour. All amino acids are joined through peptide bond. Proteins are broadly classified as globular proteins and fibrous proteins. Globular proteins are water soluble, whereas fibrous proteins are not. The complete structure of protein is discussed at four different levels i.e. primary, secondary, tertiary and quaternary structures. Protein loses its biological activity in denatured form. (a) Define the following : (i) Peptide linkage (ii) Denatured protein (b) Why do amino acids show amphoteric behaviour ? (c) (i) How can you differentiate between Fibrous protein and Globular protein ? OR (c) (ii) Write the names of two different secondary structures of proteins.

(a) (i) Calculate Ecell of a galvanic cell in which the following reaction takes place at 25 °C : Zn(s) + Pb²⁺(0·02M) longrightarrow Zn²⁺(0·1M) + Pb(s) [Given : E°Zn²⁺/Zn = -0·76V, E°Pb²⁺/Pb = -0·13V; log 2 = 0·3010, log 4 = 0·6021, log 5 = 0·6990]. (ii) State Faraday's first law of electrolysis. How much electricity, in terms of Faraday, is required to reduce one mol of MnO₄^- to Mn²⁺ ion ? OR (b) (i) The resistance of a conductivity cell containing 0·001 M KCl solution at 298 K is 1000 ohm. What is the cell constant if conductivity of 0·001 M KCl solution at 298 K is 0·125 × 10⁻³Scm⁻¹ ? (ii) Calculate the EMg²⁺/Mg potential for the following half cell at 25 °C : Mg/Mg²⁺(1 × 10⁻⁴M); E°Mg²⁺/Mg = +2·36V [Given : log 10 = 1] (iii) What is the effect of temperature on the electrical conductance of metallic conductor ?

(a) (i) Account for the following : (I) Orange colour of Cr₂O₇²⁻ ion changes to yellow when treated with an alkali. (II) Zn, Cd and Hg are non-transition elements. (III) E° value for Mn³⁺/Mn²⁺ couple is highly positive (+1·57 V) as compared to Cr³⁺/Cr²⁺. (ii) What happens when : (I) Manganate ion undergoes disproportionation reaction in acidic medium ? (II) KMnO₄ is heated ? OR (b) Answer the following questions : (i) What is 'Misch metal' ? Give its one use. (ii) Write the formula of an oxoanion of chromium in which it shows the oxidation state equal to its group number. (iii) Why does Vanadium pentoxide (V₂O₅) act as a catalyst ? (iv) Why do transition elements have high enthalpies of atomisation ? (v) How do you prepare Na₂Cr₂O₇ from Na₂CrO₄ ?

(a) (i) Identify A, B and C in the following reactions : Toluene (C₆H₅CH₃, drawn ring bearing -CH₃) + CrO₃ xrightarrow[273-283K](CH₃CO)₂O A xrightarrowH₃O^+ B xrightarrowConc. NaOH C + Sodium benzoate (C₆H₅COONa, drawn ring bearing -COONa) (ii) Give reasons for the following : (I) Carboxylic acids do not give the characteristic reactions of carbonyl group. (II) Ethanoic acid is a stronger acid than ethanol. OR (b) (i) Write the product(s) in the following reactions : (I) 2CH₃COOH xrightarrow[Δ]P₄O₁₀ (II) Benzoyl chloride (C₆H₅COCl, drawn ring bearing -COCl) + (CH₃)₂Cd longrightarrow (III) Benzene-1,2-dicarboxamide (drawn: benzene ring bearing two adjacent -CONH₂ groups) xrightarrowstrong heating (ii) Write the reaction involved in the following : (I) Wolff-Kishner reduction (II) Decarboxylation reaction