Uttarakhand Ubse Class 12 Chemistry — Real Previous-Year Papers

The reagent X in the reaction C₆H₅NH₂ (aniline) —X / 273K→ C₆H₅N₂⁺Cl⁻ (benzenediazonium chloride) is – (a) (i) HNO₃ (b) (ii) NaNO₂ and HCl (c) (iii) NaCl and HNO₃ (d) (iv) NaNO₂ and H₂SO₄

For a reaction A+B+C→ Product, the rate law is expressed as, r=k[A]^(1/2)[B]^(1/3)[C]^(1/4), then the total order of reaction is- (a) (i) 13/11 (b) (ii) 13/14 (c) (iii) 12/13 (d) (iv) 13/12

When Phenol is distilled with zinc powder, it gives- (a) (i) Benzene (b) (ii) Toluene (c) (iii) Benzaldehyde (d) (iv) Benzoic acid

Assertion (A): Formaldehyde molecule has a planer geometry. Reason (R): Carbon present in it is sp³ hybridised. (a) (i) Both A and R are correct and R is the correct explanation of A. (b) (ii) Both A and R are correct but R is not the correct explanation of A. (c) (iii) A is correct but R is incorrect. (d) (iv) Both A and R are incorrect.

What is the coordination number of Fe in [Fe(EDTA)]⁻?

What is the potential difference between the two electrodes of the galvanic cell called?

Write the name of two polysaccharides found in plants.

Fill in the blank- The solutions which obey ......... law over the entire range of concentration are known as ideal solutions.

Complete the following reactions: (a) Phenetole (a benzene ring bearing –OC₂H₅) + conc.H₂SO₄ / conc.HNO₃ → (b) (CH₃)₃C—OC₂H₅ + HI →

If the crystal field splitting energy for octahedral complex [CoCl₆]⁴⁻ is 18000 cm⁻¹, then calculate the value of crystal field splitting energy for tetrahedral complex [CoCl₄]²⁻.

Sucrose is dextrorotatory, but the mixture obtained after hydrolysis is Leavorotatory. Explain.

(a) Name one ore each of manganese and chromium. (b) Give the general electronic configuration of actinoids.

The sketch of a plant for carrying out a process is given below - Now answer the questions that follow: (a) Name the process occurring in the plant. (b) To which container does the net flow of solvent take place? (c) Name one SPM which can be used in this plant. (d) Write one practical use of the plant.

Write 'true' or 'false' about the following statements: (a) Aromatic 1° amines can be prepared by Gabriel Pthalimide synthesis. (b) Benzene Sulphonyl Chloride is known as Hinsberg's reagent. (c) pKb of aniline is more than that of methylamine. (d) Aniline undergoes Friedel-Crafts reaction.

What is Kohlrausch law of independent migration of ions? Write its one application.

Match the reactions given in Column-I with the names given in Column-II. Column-I: (i) Ar–X + Na + R–X — Dry Ether → Ar–R + NaX (ii) 2 Ar–X + 2Na — Dry Ether → Ar–Ar (biphenyl) + 2NaX (iii) C₂H₅Cl + NaI — Dry Acetone → C₂H₅I + NaCl (iv) CH₃Br + AgF → CH₃F + AgBr Column-II: 1. Swarts reaction 2. Finkelstein reaction 3. Wurtz-Fittig reaction 4. Fittig reaction

Following data are obtained for the reaction- N₂O₅ → 2NO₂ + ½O₂ t/s: 0 | 300 | 600 [N₂O₅]/mol L⁻¹: 1.6×10⁻² | 0.8×10⁻² | 0.4×10⁻² Prove that it follows first order reaction.

The value of equilibrium constant (Kc) for the reaction A(s)+B²⁺(aq) ⇌ A²⁺(aq)+B(s) is 10. Calculate the value of E°cell.

(a) 18 g of glucose is dissolved in 1kg of water in a saucepan. At what temperature this solution will boil at 1 atm. pressure? Kb for water is 0.52 K kg mol⁻¹ and boiling point is 373.15 K at 1 atm. (b) What is meant by Cryoscopic Constant?

How will you differentiate in following? (a) Glycosidic linkage and peptide linkage (b) Fibrous protein and Globular protein

Give two reactions that show the acidic nature of phenol. Compare acidity of phenol with that of ethanol.

Explain the following: (a) Secondary batteries (b) Cell constant (c) Standard Electrode potential

An aromatic compound 'A' on treatment with aqueous ammonia and heating forms compound 'B' which on heating with Br₂ and KOH form a compound 'C' of molecular formula C₆H₇N. Write the structures and IUPAC names of compounds A, B and C.

Explain the following: (a) Racemic mixture (b) Freons (c) Stereocentre

Distinguish between: (a) Homoleptic and Heteroleptic complexes (b) Double salt and a complex (c) Inner orbital complex and outer orbital complex

Give simple chemical tests to distinguish between the following pairs of compounds- (a) Pentan-2-one and Pentan-3-one (b) Benzaldehyde and Acetophenone (c) Benzoic acid and Ethyl benzoate

When an oxide of manganese (A) is fused with KOH in the presence of air and dissolved in water, dark green compound (B) is obtained. Compound (B) disproportionates in neutral or acidic medium to give purple compound (C). Compound (C), in alkaline medium, oxidises potassium iodide solution to compound (D) and compound (A) is also formed. Identify compounds A to D and explain the reactions involved.

(a) A reaction is first order with respect to reactant A and second order with respect to reactant B. Write differential rate equation. (b) If the rate constant of a reaction is k=3×10⁻⁴ s⁻¹, then what would be the order of reaction? (c) Match the statements given in Column I with Column II: Column I: (i) Mathematical expression for rate of reaction (ii) Fraction of molecules with energy equal to or greater than activation energy (iii) Order of complex reaction (iv) CH₃COOC₂H₅ + H₂O —H⁺→ CH₃COOH + C₂H₅OH Column II: (a) The slowest step (b) Pseudo first order (c) Rate law (d) e^(−Ea/RT)

Read the following passage carefully and answer the questions given below – Carboxylic acids are reduced to corresponding primary alcohols by Lithium aluminium hydride (LiAlH₄) or with diborane (B₂H₆). Diborane does not easily reduce functional groups such as ester, nitro, halo etc. Carboxylic acids having an α-hydrogen, on treatment with chlorine or bromine in the presence of small amount of red phosphorus give α-halocarboxylic acids. Sodium salts of carboxylic acids upon heating with soda lime (NaOH and CaO in the ratio of 3:1) lose carbon dioxide and hydrocarbons are formed. Aromatic carboxylic acids undergo electrophilic substitution reactions in which the carboxyl group acts as a deactivating and meta-directing group. They however, do not undergo Friedel-Crafts reaction because the carboxyl group is deactivating and the catalyst aluminium chloride (Lewis acid) gets bonded to the carboxyl group. (a) How will you convert ethanoic acid to 2-bromoethanoic acid? Give only chemical equation. (b) Benzoic acid does not undergo Friedel-Crafts reaction. Give reason. (c) Complete the following reaction: R—COOH —(i)B₂H₆ / (ii)H₃O⁻→ (d) What happens when sodium ethanoate is heated with sodalime? Give only chemical equation.