Central Board of Secondary Education

CLASS XII BOARD EXAMINATION

CHEMISTRY (043) — PRACTICE QUESTION PAPER

Time allowed: 3 hours Maximum Marks: 70
Roll No.: ____________________ Q.P. Code: 2309-2  |  Set: A

General Instructions:

  1. There are 33 questions in this question paper. All questions are compulsory.
  2. This question paper is divided into five sections – Section A, Section B, Section C, Section D, and Section E.
  3. Section A – Question numbers 1 to 12 are multiple-choice type questions (1 mark each) and question numbers 13 to 16 are Assertion-Reason type questions (1 mark each). Total marks = 16.
  4. Section B – Question numbers 17 to 21 are very short answer type questions (2 marks each).
  5. Section C – Question numbers 22 to 28 are short answer type questions (3 marks each).
  6. Section D – Question numbers 29 and 30 are case-based questions (4 marks each).
  7. Section E – Question numbers 31 to 33 are long answer type questions (5 marks each).
  8. There is no overall choice. Internal choices have been provided in selective questions.
  9. Use of calculators and log tables is not allowed.
SECTION A (16 Marks)
1. A solution is prepared by dissolving 46 g of ethanol (M = 46 g/mol) in 54 g of water (M = 18 g/mol). The mole fraction of ethanol is:
(A) 0.25      (B) 0.46      (C) 0.33      (D) 0.75
2. Assuming complete ionisation, which of the following aqueous solutions has the lowest freezing point?
(A) 0.1 m glucose      (B) 0.1 m NaCl      (C) 0.1 m K2SO4      (D) 0.1 m urea
3. Which of the following undergoes the SN1 reaction fastest?
(A) CH3Br      (B) CH3CH2CH2Br      (C) (CH3)2CHBr      (D) (CH3)3CBr
4. An optically active compound X (C4H9Br), on heating with alcoholic KOH, gives a mixture of but-1-ene and but-2-ene. X is:
(A) 2-Bromobutane      (B) 1-Bromobutane      (C) 1-Bromo-2-methylpropane      (D) 2-Bromo-2-methylpropane
5. Which of the following gives turbidity immediately with Lucas reagent at room temperature?
(A) 2-Methylpropan-1-ol      (B) 2-Methylpropan-2-ol      (C) Butan-1-ol      (D) Butan-2-ol
6. Compound Z gives a violet colour with neutral FeCl3. On heating with CHCl3 and aqueous NaOH, followed by acidification, it gives salicylaldehyde. Z is:
(A) Benzyl alcohol      (B) Anisole      (C) Cyclohexanol      (D) Phenol
7. Which of the following does NOT undergo the Cannizzaro reaction?
(A) CH3CHO      (B) HCHO      (C) C6H5CHO      (D) (CH3)3CCHO
8. The pKa values of some acids are: CH3COOH (4.76); ClCH2COOH (2.86); Cl2CHCOOH (1.29); CH3CH2COOH (4.87). Which conclusion is supported by these data?
(A) Electron-donating alkyl groups increase acidity by stabilising the carboxylate ion.
(B) Introducing chlorine decreases acidity because of its -I effect.
(C) Electron-withdrawing substituents stabilise the carboxylate ion, and the effect increases with the number of Cl atoms.
(D) Acid strength is independent of the substituent on the α-carbon.
9. 18 g of glucose (M = 180 g/mol) is dissolved in 178.2 g of water (M = 18 g/mol). The relative lowering of vapour pressure is:
(A) 0.10      (B) 0.01      (C) 0.001      (D) 0.02
10. Which of the following is most reactive towards nucleophilic substitution with aqueous NaOH?
(A) 1-Chloro-4-nitrobenzene      (B) Chlorobenzene      (C) 1-Chloro-4-methylbenzene      (D) 1-Chloro-4-methoxybenzene
11. Which of the following does NOT give a yellow precipitate with I2/NaOH?
(A) Ethanol      (B) Propan-2-ol      (C) Pentan-3-one      (D) Propanone
12. Ethanol is heated with excess conc. H2SO4. The major products at 413 K and at 443 K respectively are:
(A) ethene; ethoxyethane      (B) ethoxyethane; ethene      (C) ethanal; ethene      (D) ethoxyethane; ethanal

Questions 13 to 16 are Assertion (A) and Reason (R) type questions. Select the correct option:
(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 true.

13. Assertion (A): The molality of a solution does not change with temperature, but its molarity does.
Reason (R): Molality is defined using the mass of solvent, whereas molarity is defined using the volume of solution.
14. Assertion (A): Chlorobenzene is less reactive than chloroethane towards nucleophilic substitution.
Reason (R): The C–Cl bond in chlorobenzene has partial double-bond character due to resonance.
15. Assertion (A): Anisole reacts with HI to give iodobenzene and methanol.
Reason (R): The C(sp2)–O bond in anisole has partial double-bond character, and the phenyl cation is unstable.
16. Assertion (A): Ethanal is more reactive than propanone towards nucleophilic addition.
Reason (R): The carbonyl carbon of propanone is more electrophilic than that of ethanal because of two +I methyl groups.
SECTION B (10 Marks)
17. At 298 K, Henry's law constant (KH) for CO2 in water is 1.67 × 103 bar. A sealed soft-drink bottle has CO2 at a partial pressure of 3.34 bar above the liquid.
(i) Calculate the mole fraction of CO2 dissolved.
(ii) Why does the drink fizz when the bottle is opened?
OR
A student tries to obtain absolute alcohol by fractional distillation of an ethanol-water mixture, but the distillate never exceeds 95.6% ethanol.
(i) Name the type of mixture formed and the type of deviation from Raoult's law shown.
(ii) Why can the components not be separated further by distillation?
18. Arrange 1-bromobutane, 2-bromobutane and 2-bromo-2-methylpropane in increasing order of boiling point. Give a reason.
19. Give one chemical test (with the observation) to distinguish between:
(i) ethanol and phenol
(ii) propan-1-ol and propan-2-ol
20. An aldehyde A (C3H6O) reacts with dilute NaOH to give B (C6H12O2), which on heating gives C (C6H10O). Write the structures of A, B and C and name the reaction.
OR
A compound X (C7H6O) gives a positive Tollens' test. On heating with conc. NaOH it gives Y and Z; Y on acidification gives a compound of formula C7H6O2. Identify X, Y and Z and name the reaction.
21. Write the major organic product in each case:
(i) Chlorobenzene + CH3Cl + Na (dry ether)
(ii) CH3CH2Br + AgNO2 (alcoholic)
SECTION C (21 Marks)
22. 1.5 g of ethanoic acid (M = 60 g/mol) is dissolved in 50 g of benzene. The observed depression in freezing point is 1.6 K (Kf of benzene = 5.12 K kg mol-1). Ethanoic acid dimerises in benzene. Calculate:
(i) the van't Hoff factor,
(ii) the percentage association.
23. The total vapour pressure of mixtures of liquids X and Y at 300 K was measured. Pure X has vapour pressure 200 mm Hg and pure Y has 100 mm Hg.
• Mole fraction of X: 0.25      0.50      0.75
• Observed total pressure (mm Hg): 118      130      165
(i) Calculate the total pressure expected from Raoult's law at XX = 0.50.
(ii) Which type of deviation does the mixture show? Justify using the data.
(iii) Predict the signs of ΔmixH and ΔmixV, and give one example of such a pair of liquids.
24. Write the major product and the type of reaction:
(i) (CH3)3C–Br + C2H5ONa, heated in ethanol
(ii) CH3CH2CH2Cl + NaI in dry acetone
(iii) C6H5Br + Mg in dry ether
25. How will you convert:
(i) Propene to propan-1-ol
(ii) Phenol to 2-hydroxybenzoic acid
(iii) Cumene to phenol
26. P, Q and R are isomers of molecular formula C7H8O.
• P dissolves in aqueous NaOH and gives a violet colour with neutral FeCl3.
• Q is insoluble in NaOH and liberates H2 with sodium. On oxidation with PCC it gives a compound that reduces Tollens' reagent.
• R does not react with sodium or NaOH. On heating with HI it gives phenol and CH3I.
Identify P, Q and R.
27. Write the structure of the product and name the reaction:
(i) CH3COCl + H2, Pd-BaSO4
(ii) C6H5CH3 + CrO2Cl2 in CS2, followed by H3O+
(iii) CH3CH2CN + SnCl2/HCl, followed by H3O+
28. A compound A (C4H8O) forms an orange precipitate with 2,4-DNP, does not reduce Tollens' reagent, and gives a yellow precipitate with I2/NaOH.
(i) Identify A.
(ii) Write the product when A is heated with NH2NH2 followed by KOH in ethylene glycol.
(iii) Write the products of the reaction of A with I2/NaOH.
SECTION D (8 Marks)
29. Case-Based Question 1:
A student tested four colourless liquids/solids P, Q, R and S (phenol, ethanol, ethoxyethane and 2-methylpropan-2-ol, in some order) and recorded the following:
Test P Q R S
Sodium metal H2 evolved H2 evolved No reaction H2 evolved
Dissolves in aq. NaOH Yes No No No
Neutral FeCl3 Violet No colour No colour No colour
Lucas reagent, room temp. No turbidity No turbidity No turbidity Turbidity within seconds
(i) Identify P and R.
(ii) Why does P dissolve in aqueous NaOH while Q does not?
(iii) Write the reaction of Q with conc. H2SO4 at 443 K and name the type of reaction.
(iv) Why does S give turbidity immediately with Lucas reagent?
OR
(iv) Write the equation for the reaction of P with bromine water and state the observation.
30. Case-Based Question 2:
Vinegar contains ethanoic acid, which can be made by oxidising ethanal. A student performed three tests:
• Test 1: ethanoic acid + aqueous NaHCO3 gave brisk effervescence.
• Test 2: phenol + aqueous NaHCO3 gave no effervescence.
• Test 3: ethanal + Tollens' reagent, warmed, gave a silver mirror.

(i) Explain the observations in Tests 1 and 2.
(ii) Write the equation for Test 3.
(iii) Name the product formed when ethanoic acid is heated with ethanol and conc. H2SO4, and name the reaction.
(iv) Arrange CH3COOH, FCH2COOH and ClCH2COOH in increasing order of acid strength.
OR
(iv) Why do carboxylic acids have higher boiling points than alcohols of comparable molar mass?
SECTION E (15 Marks)
31. 5.85 g of NaCl (M = 58.5 g/mol) is dissolved in 1 kg of water. NaCl is 90% dissociated in this solution. (Kf = 1.86 K kg mol-1, Kb = 0.52 K kg mol-1; freezing point of water = 273.15 K, boiling point of water = 373.15 K).
(i) Calculate the molality of the solution.
(ii) Calculate the van't Hoff factor.
(iii) Calculate the freezing point of the solution.
(iv) Calculate its boiling point.
OR
Liquids A and B form an ideal solution. At 300 K the vapour pressures of pure A and pure B are 200 mm Hg and 100 mm Hg respectively. A solution contains 2 mol of A and 3 mol of B.
(i) State Raoult's law.
(ii) Calculate the total vapour pressure.
(iii) Calculate the mole fraction of A in the vapour phase.
(iv) Which component is more volatile, and how does the vapour composition show this?
32. Identify A, B, C, D and E:

CH3CH2CH2Br  →alc. KOH, Δ  A  →HBr, no peroxide  B  →aq. KOH  C  →Cu, 573 K  D  →I2/NaOH  E

OR
(a) Write the two-step mechanism for the hydrolysis of 2-bromo-2-methylpropane with aqueous KOH and give the rate law.
(b) Haloalkanes give alkyl cyanides with KCN but isocyanides with AgCN. Explain.
33. An organic compound X (C5H10O) forms an orange precipitate with 2,4-DNP, does not reduce Tollens' reagent and does not give the iodoform test. Vigorous oxidation of X with KMnO4/KOH gives ethanoic acid and propanoic acid.
(a) Identify X and justify your answer.
(b) Write the product of X with NH2OH.
(c) Write the product of X with NaBH4.
(d) Write the product of X with Zn–Hg/conc. HCl.
OR
(i) Give a chemical test to distinguish: (a) propanal and propanone, (b) benzoic acid and ethyl benzoate.
(ii) Write the product and name the reaction:
    (a) CH3CH2COOH + Cl2/red P, then H2O
    (b) HCHO + conc. NaOH
    (c) CH3CHO + dil. NaOH, cold
--- End of Question Paper ---
Hosted & Compiled with HtmlRunner.com