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ISC Class XII Prelims 2026 : Chemistry

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Lucknow University (LU), Lucknow
Bachelor of Education Education and Psychology

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UNSTOPPABLE ACADEMIC CLASSES FIRST PRELIMINARY EXAMINATION 2025-26 ISC Chemistry (Theory) Max Marks: 70 Time Allotted: 3 hours Reading Time: Additional Fifteen minutes Instructions to candidates 1. All questions are compulsory. Internal choices are provided where indicated. 2. The paper is divided into four sections A, B, C, D. 3. Section A (14 marks): Q1 with subparts (objective/very short). 4. Section B (20 marks): 10 questions 2 marks. (with one internal choice). 5. Section C (21 marks): 7 questions 3 marks (with one internal choice). 6. Section D (15 marks): 3 questions 5 marks (with one internal choice). 7. Show essential working for numerical. Use balanced equations/diagrams where helpful. 8. Figures to the right indicate marks [ ]. 9.In working out problems use following data: Gas constant R = 1.987cal deg 1 mol 1 = 8.314 JK 1 mol 1 = 0.082l dm3 atm K 1 mol 1 1 l atm = 1 dm3 atm = 101.3 J, 1 Faraday = 96500 coulombs Avogadro s number = 6.023 1023 SECTION A 14 Marks Question 1. (A) Fill in the blanks by choosing the appropriate word(s) given in the brackets: [primary cell, secondary cell, phosgene, diethyl carbonate, paramagnetic, diamagnetic, associated, dissociated, square-planar, tetrahedral] [4 1] 1. A _____ is an example of a primary source of electrical energy, while a _____ can be recharged and used multiple times. 2. Addition of a small amount of ethanol to chloroform prevents formation of the toxic gas _____ and converts it to the safer compound _____. 3. A complex with one unpaired electron is _____ in nature. 4. The geometry around dsp2 hybridised complexes is typically _____. (B) Select and write the correct alternative from the choices given below. [7 1] (i). In a dry cell, the _____ acts as the anode and the graphite rod acts as the cathode. (a) zinc container (b) carbon paste (c) MnO2 (d) NH4Cl (ii). Which one of the following can produce the foul smelling compound methyl isocyanide in presence of alcoholic KOH? (a) Chloroform and aniline (b) Chloroform and methanol (c). Chloroform and dimethyl amine (d) Chloroform and methyl amine (iii) An equimolal solution of non-volatile solutes A and B, shows a depression in freezing point in the ratio of 2:1. If A remains in its normal state in the solution, the state of B in the solution will be: (a) normal. (b) hydrolysed. (c) associated. (d) dissociated 1 (iv) The coordination number and the oxidation state of the central metal D in the complex [D(en) 2(H2O)2] Cl3 are: (a) 6 and 2, respectively (b) 4 and 2, respectively (c) 3 and 6, respectively (d) 6 and 3, respectively (v) The metal complex ion that is paramagnetic is (Atomic number of Fe = 26, Cu = 29, Co = 27 and that of Ni = 28) (a) [Fe(CN)4] 2 (b) [Co(NH3)6] 3+ (c) [Ni(CN)4]2 (d) [Cu(NH3)4] 2+ (vi) Assertion: The process of halogenation of benzene takes place in the presence of anhydrous FeCl3. Reason: Anhydrous FeCl3 prepares nucleophile to attack the benzene ring. (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion. (b) Both Assertion and Reason are true but Reason is not the correct explanation for Assertion. (c) Assertion is true and Reason is false. (d) Both Assertion and Reason are false. (vii) Assertion: Specific conductivity of all electrolytes decreases on dilution. Reason: On dilution, the number of ions per unit volume decreases. (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion. (b) Both Assertion and Reason are true but Reason is not the correct explanation for Assertion. (c) Assertion is true but Reason is false. (d) Assertion is false but Reason is true. (C) Read the passage given below and answer the questions that follow. [3 1] When two solutions are separated by a semipermeable membrane, the solvent molecules move from a solution of lower molar concentration to a solution of higher molar concentration through osmosis. (i) Rakshita a class XII student removed the outer hard shell of two different eggs while cooking at home. She then placed one egg in pure water and the other egg in saturated solution of sucrose. What change is she likely to observe in the eggs after few hours? (ii) Which solution, hypertonic or hypotonic, has a higher amount of solute in same quantity of solution? (iii) A 5% aqueous solution of glucose (molar mass = 180 g mol 1) is isotonic with 1.66% aqueous solution of urea. Calculate the molar mass of urea. SECTION B 20 Marks Question 2 [2] If 200 cm3 of an aqueous solution of a protein contains 1.26 g of protein, the osmotic pressure of the solution at 300K is found to be 2.57 10 3 atm. Calculate the molar mass of protein. (R = 0.0821 L atm K 1 mol 1) Question 3. Give one chemical test to distinguish between the following: (i) ethanol and phenol (ii) Propan-2-ol and tert-butyl alcohol [2] Question 4. [2] Explain why molar conductivity increases with dilution for weak electrolyte. Sate Kohlrausch law of independent migration. Question 5. Write the IUPAC names and classify (high-spin/low-spin) of: (i) [Co(H2O)6]3+ (ii) [FeF6]3- 2 [2] Question 6. Convert the following by giving chemical equations for each. (i) Ethyl bromide to diethyl ether (ii) Phenol to salicylaldehyde [2] Question 7. [2] Calculate the number of coulombs required to electroplate 4.75 g of aluminium when electrode reaction is Al3+ + 3e Al 1 (Given: Atomic weight of Al = 27 g mol , 1 Faraday = 96,500 coulombs) Question 8. [2] When an organic compound [A] having molecular formula C4H9Br is treated with aqueous KOH, the rate of reaction depends on concentration of compound [A] only. But when compound [B], with the same molecular formula, reacts with aqueous KOH, the rate of reaction depends on the concentration of compound [B] as well as of KOH. Compound [B] is a structural isomer of compound [A]. Identify compounds [A] and [B] Question 9. [2] (i) Calculate the maximum possible electrical work that can be obtained from a galvanic cell under standard conditions at 298 K. Zn|Zn2+(aq)|| Ag+|Ag (aq) Given E (Zn2+/Zn) = 0.76 V; E (Ag+/Ag) = + 0.80 V OR (ii) Give a reason for each of the following. (a) Ethoxy ethane does not react with sodium, but ethanol does. (b) Methoxy ethane with conc. HI at 373K gives C2H5OH and CH3I but not CH3OH and C2H5I. Question 10. Explain chelation with a suitable example of a chelating ligand used medicinally. Question 11. How will you bring the following conversions? (i) Benzene to biphenyl [2] [2] (ii) Methanol to ethanol SECTION C 21 Marks Question12. [3] According to Crystal-Field Theory, the electronic configuration of complex compound [A] is t42g e 2g and that of complex compound [B] is t62g e0g. (i) Which of the two complex compounds, [A] or [B], is a low spin complex? (ii) Write the number of unpaired electrons in complex compounds [A] and [B]. (iii) Does complex [A] have strong field ligands or weak field ligands? Give a reason Question13. [3] An aqueous solution containing 12.50 g of barium chloride in 1000g of water boils at 373.0834 K. Calculate the degree of dissociation of barium chloride. Given Kb for H2O = 0.52 K kg mol 1; molecular mass of BaCl2 = 208.34 g mol 1 3 Question 14. chemical equations to illustrate the following name reactions: [3] Write (i) Finkelstein reaction (ii) Williamson s synthesis (iii) Reimer Tiemann reaction Question 15. [3] (i) Define osmotic pressure. (ii) The osmotic pressure of blood at 37 C is 8.21 atm. How much glucose in grams should be used per litre of aqueous solution for an intravenous injection so that it is isotonic with blood? (Molecular wt. of glucose = 180g/mol). Question 16. [3] (a) Outline the mechanism of nucleophilic aromatic substitution of chlorobenzene under fused NaOH/350 C (or via benzyne). OR (b) Sketch the mechanism of electrophilic substitution of chlorobenzene when made to react with conc. HNO 3 in presence of conc. H2SO4. Question 17. How will the following be converted? (Give chemical equation) (a) Ethyl bromide to ethyl isocyanide. (b) Aniline to benzene diazonium chloride. [3] (c) Benzene diazonium chloride to phenol. Question 18. [3] (i) Assuming that cyanide is a strong ligand, write the formula of two coordination complex ions with cyanide and iron having coordination number six. Name the complex ions. (ii) On the basis of CFT, write the electronic configuration of d 4 ion if: (a) o >P (b) o <P SECTION D 15 Marks Question19. [5] (a)An aqueous solution is made by dissolving 10 g of glucose (C6H12O6) in 90 g of water at 300 K. If the vapour pressure of pure water at 300 K is 32.8 mm Hg, what would be the vapour pressure of the solution? (Given: C = 12, H = 1 and O = 16) (b) A solution containing 12.5 g of a non-electrolyte solute in 175 g of water gave boiling point of 100.70 C. Calculate the molecular mass of the solute. (Given: Kb for water = 0.52 K kg mol 1) (c) Why are soda water bottles sealed under high pressure? Question20. [5] (a) Study the diagram given below that represents Cu-Ag electrochemical cell and answer the questions that follow. Given E0 (Cu2+/Cu) = 0.337 V; E0 (Ag+/Ag) = 0.799 V 4 (1) Write the cell reaction for the above cell. (2) Calculate the standard emf of the cell. (3) If the concentration of [Cu2+] is 0.1 M and Ecell is 0.422 V, at 25 C, calculate the concentration of [Ag+]. (b) A 0.05 M NH4OH solution offers the resistance of 30.8 ohms to a conductivity cell at 298K. If the cell constant is 0.343 cm 1 and molar conductance of NH4OH at infinite dilution is 471.4 S cm 2 mol 1, calculate the following: (1) Specific conductance (2) Molar conductance Question 21. [5] (a) Phenol is an aromatic alcohol that is used to prepare many important compounds such as picric acid. Phenol is widely used in household and industrial settings as a cleaner and disinfectant. It is also used as a primary chemical to make plastics. Phenol is less soluble in water as compared to aliphatic alcohol. Some aliphatic alcohols are toxic and can be addictive. (i) How is the acid mentioned above prepared from phenol? Write the chemical reaction involved in this preparation. (ii) Phenol is less soluble in water as compared to aliphatic alcohol . Explain. (iii) Write the chemical equation for the preparation of phenol from chlorobenzene. (iv) An organic compound [A] having molecular formula C4H10O gives positive Lucas test within five minutes at room temperature. Compound [A] upon oxidation with K 2Cr2O7/H2SO4 forms compound [B] which gives positive iodoform test. Identify compounds [A] and [B]. (v) Give coupling reaction test of phenol. (Give reaction) OR Question 21 [5] (b) (i) A coordination compound has a formula CoCl3.4NH3. It precipitates silver ions as AgCl and its molar conductance corresponds to a total of two ions. Based on this information, answer the following questions. (1) Deduce structural formula of the complex compound. (2) Write the IUPAC name of the complex compound. (3) Draw the geometrical isomers of the complex compound. (ii) Give a chemical test to show that [Co(NH3)5Cl]SO4 and [Co(NH3)5SO4]Cl are ionisation isomers. 5

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