Manipur Cohsem Class 12 Chemistry — Real Previous-Year Papers

In an acid-base titrimetric analysis, the concentration of a sulphuric acid analyte is found to be 0.044 M. The strength of the acid in g/L is – (a) 0.44 (b) 4.31 (c) 2.15 (d) 44.00

Regarding Gabriel synthesis for amines, which of the following statements is correct? (a) All types of amines can be synthesized (b) Only aromatic amines can be synthesized (c) Only aliphatic amines can be synthesized (d) Only aliphatic primary amines can be synthesized

In the disproportionation reaction 2 Cu⁺ (aq) ⇌ Cu (s) + Cu²⁺ (aq), the cuprous ion, Cu⁺ (a) undergoes reduction only (b) undergoes both reduction and oxidation (c) undergoes oxidation only (d) does not undergo redox

A reaction is found to be 50% complete in 20 minutes and 75% complete in 30 minutes. The order of the reaction is – (a) 0 (b) 0.5 (c) 1 (d) 2

Which one of the following metal ions is likely to have a magnetic moment of 1.73 BM? (a) Fe²⁺ (b) Mn²⁺ (c) Cr²⁺ (d) Cu²⁺

The structure of a valuable organic compound used as solvent in many chemical industries is shown below (a central carbon bearing a CH₃ group above, a CH₃ group to the left, an OH group below, and a –CH₂–OCH₃ group to the right). The IUPAC name of the organic compound is (a) 1-methoxy-2-methylpropan-2-ol (b) 3-methoxy-2-methylpropan-2-ol (c) 1-methoxy-3-methylpropan-3-ol (d) 2-methoxy-2-methylpropan-2-ol

Ethanoic acid (pKa = 4.76) on treatment with Cl₂ / red phosphorus gives a derivative of ethanoic acid. The ethanoic acid derivative will have – (a) pKa > 4.76 (b) pKa < 4.76 (c) pKa = 4.76 (d) pKa = 0.00

Which of the following characters of D-(+)-Glucose CANNOT be explained by the open chain structure? (a) D- and L- forms (b) (+) and (–) forms (c) α- and β- forms (d) pentaacetate formation

Assertion (A): Among the structural isomers of C₄H₉Br, only 2-bromobutane is optically active. Reason (R): It contains one asymmetric carbon and exists in two enantiomeric forms. (a) Both A and R are true and R is the correct explanation of A. (b) Both A and R are true but R is not the correct explanation of A. (c) A is true but R is false. (d) A is false but R is correct.

Assertion (A): Glycinate ion H₂NCH₂COO⁻ is a chelating ligand. Reason (R): It can link through either nitrogen or anionic oxygen. (a) Both A and R are true and R is the correct explanation of A. (b) Both A and R are true but R is not the correct explanation of A. (c) A is true but R is false. (d) A is false but R is correct.

Write the statements of Faraday's two laws of electrolysis.

A solution contains 0.150 mole fraction urea (H₂NCONH₂) and 0.850 mole fraction water. Calculate the molality of the solution.

Why do actinides have lower first ionisation enthalpy as compared to the lanthanides (specially for the early elements)?

Daniel cell has the cell reaction Zn (s) + Cu²⁺ (aq) → Zn²⁺ (aq) + Cu (s). Draw a qualitative plot showing change in Ecell as a function of log([Zn²⁺]/[Cu²⁺]) as current is supplied by the cell and show the point at which Ecell is equal to E°cell.

For a chemical reaction carried out at different temperatures (T), the plot of log k against 1/T is found to be a straight line with slope –1.2 × 10⁴. Calculate the activation energy of the reaction (Given, R = 8.314 J mol⁻¹ K⁻¹).

The complex tetraamminenickel(II) chloride is found to be paramagnetic in nature. Draw its d-orbital splitting diagram and show the electron distribution.

Haloalkanes have higher boiling points than the hydrocarbons of comparable molecular mass. Give reason.

Outline a synthetic strategy for butan-2-ol starting from ethanal.

Identify the products of the following named reactions: (i) propan-2-one (CH₃COCH₃) on Clemmensen reduction; (ii) benzonitrile (C₆H₅CN) on Stephen reaction.

Mention the two essential components of a nucleoside.

The carbonyl carbon of aldehydes and ketones is a good site for nucleophilic addition. Illustrate it with a suitable example.

The oxidation of nitrogen monoxide (NO) with oxygen (O₂) to produce nitrogen dioxide (NO₂) proceeds through the following mechanism: Step 1. NO (g) + O₂ (g) ⇌ NO₃ (g) [fast, equilibrium; forward rate constant K₁, backward K₋₁]; Step 2. NO₃ (g) + NO (g) → 2 NO₂ (g) [slow; rate constant K₂]. Based on the mechanism find out the rate law and identify the intermediate.

Give reason: (i) Amines act as nucleophile. (ii) Aliphatic amines are more basic than ammonia.

Discuss the synergic bonding between the ligand and the metal atom in the homoleptic metal carbonyls according to VB theory.

The reaction of zinc metal and chlorine gas is utilized in a voltaic cell in which zinc ions and chloride ions are formed in aqueous solution: Zn (s) + Cl₂ (g) → Zn²⁺ (aq) + 2 Cl⁻ (aq). Calculate the standard emf of the cell and obtain ΔG° for the cell reaction. (Given: standard reduction potential, Zn²⁺/Zn = –0.76 V, Cl₂/Cl⁻ = 1.36 V)

Case study: Alcohols and phenols have hydroxyl group as their functional group. The properties of alcohols and phenols are chiefly due to the hydroxyl group. The nature of alkyl and aryl groups simply modify these properties. Boiling points of alcohols and phenols are higher in comparison to other classes of compounds, namely hydrocarbons, ethers, haloalkanes and haloarenes of comparable molecular masses. The polar nature of the functional group is responsible for acidic character of alcohols and phenols. Groups which increase electron density on oxygen tend to decrease the polarity of O–H bond whereas electron withdrawing groups give opposite effect. The same effects are also responsible for the other chemical properties and reactions of alcohols and phenols. (a)(i) Why is ethanol less acidic than water? (ii) What will happen when sodium metal is added to phenol?

Equimolar amounts of two non-volatile compounds AB(s) and XY(s) are dissolved separately in 1 L of water each. In solution they undergo the changes: AB(s) → A⁺ (aq) + B⁻ (aq); XY(s) → XY (aq). (a)(i) Derive the relationship between molecular mass of the compound XY and relative lowering of vapour pressure. (ii) Which of the two solutions will have higher boiling point? Give reason.

How is potassium permanganate prepared from pyrolusite ore? Write its redox reactions in acid medium with (i) KI and (ii) ferrous sulphate solutions.

A saturated hydrocarbon isomer (A) (C₅H₁₂) on monochlorination with Cl₂/UV light gives only one product (B) which reacts with aqueous KOH to form product (C). Deduce the structure of (A), (B), (C) and write the sequence of reactions. Write the mechanism involved in the reaction of (B) to produce (C).