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Paper pattern

A · all 16 · 1 mark each · 12 multiple choice and 4 assertion-reason16

B · all 5 · 2 marks each · very short answer10

C · all 7 · 3 marks each · short answer21

D · all 2 · 4 marks each · case-based, a passage or data then sub-questions8

E · all 3 · 5 marks each · long answer, internal choice in all three15

Board paper total70

CBSE Chemistry (043) Class XII question paper design and sample question paper, 2026-27: 33 questions, 70 marks, 3 hours, about a third of the questions with an internal choice.

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2 marks · short answer

Define molality. Why is it preferred to molarity when a solution is studied at different temperatures?Unit I State Henry's law. Why are the air tanks of scuba divers diluted with helium?Unit I What is an azeotrope? Which type is formed by a solution that shows a large negative deviation from Raoult's law? Give one example.Unit I What is reverse osmosis? Name a material that can be used as the membrane for it.Unit I What is meant by an abnormal molar mass? Why does KCl show a molar mass lower than its true value when found from the freezing point of its aqueous solution?Unit I Give two functions of the salt bridge in a galvanic cell. What would the voltmeter show if the salt bridge were removed?Unit II Why is alternating current, and not direct current, used to measure the conductivity of an electrolytic solution? Write the SI unit of molar conductivity.Unit II Predict the products at each electrode when aqueous CuSO₄ solution is electrolysed using (i) platinum electrodes and (ii) copper electrodes.Unit II Why does a mercury cell give a constant voltage throughout its life? Write its overall cell reaction.Unit II How does galvanising protect iron from rusting, even where the zinc coating is scratched?Unit II Distinguish between the average rate and the instantaneous rate of a reaction. How is the instantaneous rate found from a concentration-time graph?Unit III For a reaction, rate = k[A]^(3/2)[B]^(−1/2). What is its overall order? Write the unit of k.Unit III Give two differences between the order and the molecularity of a reaction.Unit III Show that the half-life of a first order reaction does not depend on the initial concentration of the reactant.Unit III How does a catalyst increase the rate of a reaction? Draw an energy profile diagram with and without a catalyst.Unit III Why are Zn, Cd and Hg not regarded as transition elements, though they are placed in the d-block?Unit IV Calculate the spin-only magnetic moment of Fe³⁺ (Z = 26) and state whether the ion is coloured in solution.Unit IV E°(Cu²⁺/Cu) is +0.34 V while the other 3d metals have negative values. Explain why.Unit IV Why do transition metals and their compounds act as catalysts? Name the catalyst used in the Haber process.Unit IV What happens when potassium permanganate is heated to 513 K? Write the equation.Unit IV Write the IUPAC name of [CoCl₂(en)₂]Cl. State the oxidation state and the coordination number of cobalt in it.Unit V What is an ambidentate ligand? Name the type of isomerism it can cause and give one example of such a pair of isomers.Unit V How will you distinguish between [Co(NH₃)₅(SO₄)]Br and [Co(NH₃)₅Br]SO₄ by one chemical test each?Unit V Explain, with a simple sketch, the synergic bonding between a metal and carbon monoxide in a metal carbonyl.Unit V [CoF₆]³⁻ is paramagnetic but [Co(C₂O₄)₃]³⁻ is diamagnetic, although both contain Co³⁺. Explain using valence bond theory.Unit V Why is thionyl chloride the preferred reagent for converting an alcohol into an alkyl chloride? Write the equation.Unit VI Write the IUPAC names of (i) (CH₃)₃CBr and (ii) CH₂=CHCH₂Cl, and say whether each is a tertiary, allylic, benzylic or vinylic halide.Unit VI o-Dichlorobenzene melts at 256 K and p-dichlorobenzene at 323 K, though both boil near 450 K. Account for the difference.Unit VI Why is chloroform stored in closed, dark coloured bottles filled to the brim? Write the equation for the reaction this prevents.Unit VI What happens when (i) bromoethane is heated with sodium in dry ether, (ii) ethylmagnesium bromide is treated with water? Write equations.Unit VI How is salicylic acid obtained from phenol? Name the reaction and write the equations.Unit VII How will you distinguish between propan-2-ol and 2-methylpropan-2-ol by a chemical test? Write what you observe.Unit VII Phenol is a stronger acid than ethanol. Give a reason.Unit VII Propan-1-ol boils at 370 K, but its isomer methoxyethane boils at about 281 K. Explain the difference.Unit VII Give the products when anisole is heated with HI. Why is phenol, and not iodobenzene, formed?Unit VII Write the IUPAC names of CH₃CH₂CH(CH₃)CHO and C₆H₅COCH₂CH₃.Unit VIII Write the Etard reaction and the Gattermann-Koch reaction, with reagents and conditions.Unit VIII Why is the pH of the medium carefully controlled when aldehydes and ketones react with ammonia derivatives? Give one example of such a reaction.Unit VIII Write the Cannizzaro reaction of methanal. Why does ethanal not undergo this reaction?Unit VIII Why is methanoic acid a stronger acid than ethanoic acid?Unit VIII Write the IUPAC names of (i) (CH₃)₂NCH₂CH₃ (ii) C₆H₅CH₂NHCH₃.Unit IX Write the Hoffmann bromamide degradation of propanamide and name the amine formed.Unit IX Arrange in increasing order of pKb and give one reason: C₆H₅NH₂, CH₃NH₂, (CH₃)₂NH, NH₃.Unit IX Why is the -NHCOCH₃ group of acetanilide a weaker activator of the benzene ring than the -NH₂ group of aniline?Unit IX Write the carbylamine reaction of ethanamine. Which class of amines does this reaction detect?Unit IX Glucose and fructose both reduce Fehling's solution, but sucrose, which is made from them, does not. Define a reducing sugar and explain why sucrose is non-reducing.Unit X Write the reactions of glucose with bromine water and with hydroxylamine. What does each reaction show about the structure of glucose?Unit X What is denaturation of a protein? What happens to its primary structure during denaturation? Give one example.Unit X Name the vitamins whose deficiency causes (i) beri beri and (ii) increased blood clotting time. Which of the two is fat-soluble?Unit X Differentiate between a nucleoside and a nucleotide, and name the linkage that joins nucleotides in a nucleic acid.Unit X

3 marks · short answer

Liquids P and Q form an ideal solution. At a certain temperature their pure vapour pressures are 300 mm Hg and 500 mm Hg. For a solution with x(P) = 0.6, find the total vapour pressure and the mole fraction of P in the vapour.Unit I A solution of 5.0 g of a non-volatile non-electrolyte in 100 g of water freezes at 272.22 K. Find the molar mass of the solute. (Kf of water = 1.86 K kg mol⁻¹; freezing point of water = 273.15 K)Unit I A 0.05 mol kg⁻¹ aqueous solution of CaCl₂ shows a freezing point depression of 0.2511 K. Calculate the van't Hoff factor and the degree of dissociation of CaCl₂. (Kf = 1.86 K kg mol⁻¹)Unit I Calculate the EMF at 298 K of the cell Ni(s) | Ni²⁺(0.01 M) || Cu²⁺(0.1 M) | Cu(s). E°(Ni²⁺/Ni) = −0.25 V; E°(Cu²⁺/Cu) = +0.34 V.Unit II For the cell reaction Fe(s) + 2Fe³⁺(aq) → 3Fe²⁺(aq), calculate E°cell and ΔrG° at 298 K. Is the reaction spontaneous? E°(Fe³⁺/Fe²⁺) = +0.77 V; E°(Fe²⁺/Fe) = −0.44 V; F = 96500 C mol⁻¹.Unit II At 298 K, a 0.0016 M solution of ethanoic acid has Λm = 39.05 S cm² mol⁻¹. Using λ°(H⁺) = 349.6 and λ°(CH₃COO⁻) = 40.9 S cm² mol⁻¹, calculate its degree of dissociation and its dissociation constant.Unit II A first order reaction is 50% complete in 40 minutes. Calculate the rate constant and the time taken for 75% of the reaction to be completed. (log 2 = 0.3010)Unit III The rate constant of a reaction becomes four times when the temperature is raised from 300 K to 320 K. Calculate the activation energy. (R = 8.314 J K⁻¹ mol⁻¹, log 4 = 0.6020)Unit III Derive the integrated rate equation for a zero order reaction and draw the graph of [R] against t. Give one example of such a reaction.Unit III For the reaction 2A + B → C, the following initial rates were found: [A] = 0.1, [B] = 0.1 mol L⁻¹, rate 3.0 × 10⁻⁴; [A] = 0.2, [B] = 0.1, rate 1.2 × 10⁻³; [A] = 0.1, [B] = 0.2, rate 6.0 × 10⁻⁴ mol L⁻¹ s⁻¹. Find the rate law and the rate constant.Unit III Give reasons: (i) Transition metals have high enthalpies of atomisation. (ii) The second ionisation enthalpy of chromium is unusually high. (iii) The atomic radii of Zr and Hf are almost the same.Unit IV Explain: (i) Mn shows the largest number of oxidation states in the 3d series. (ii) The highest oxide of Mn is Mn₂O₇ but its highest fluoride is MnF₄. (iii) Cu⁺ is unstable in aqueous solution.Unit IV What is lanthanoid contraction? State its cause and two of its consequences.Unit IV State the postulates of Werner's theory. A compound CoCl₃·5NH₃ gives 2 mol of AgCl per mole with excess AgNO₃. Write its formula and its primary and secondary valences.Unit V Draw the geometric isomers of [CrCl₂(en)₂]⁺. Which of them is optically active? Give a reason.Unit V Draw the splitting of d orbitals in an octahedral crystal field. Write the configuration of a d⁶ ion with a strong field ligand and with a weak field ligand, and give the number of unpaired electrons in each.Unit V Write the SN2 mechanism for the reaction of chloromethane with hydroxide ion. Why does chloromethane react faster than 2-chloro-2-methylpropane by this route?Unit VI Give three reasons why chlorobenzene is much less reactive than chloromethane towards nucleophilic substitution.Unit VI Define retention, inversion and racemisation. Why does the SN1 hydrolysis of optically active 2-bromobutane give an optically inactive product?Unit VI How will you convert aniline into (i) chlorobenzene and (ii) iodobenzene? Name the reaction used in (i) and write the conditions.Unit VI Show, in three steps, how conc H₂SO₄ at 443 K turns ethanol into ethene, and say which step controls the rate and why.Unit VII Starting from isopropylbenzene, show how phenol is made on a large scale. Write the equations and name the useful second product.Unit VII Using a Grignard reagent and a suitable carbonyl compound, how would you prepare (i) ethanol, (ii) propan-2-ol, (iii) 2-methylpropan-2-ol?Unit VII Explain why the C-O-H bond angle in methanol is slightly less than tetrahedral, the C-O-C angle in methoxymethane is slightly more, and the C-O bond in phenol is shorter than in methanol.Unit VII Give a simple chemical test to distinguish between: (i) ethanal and propanone (ii) ethanal and benzaldehyde (iii) phenol and ethanoic acid.Unit VIII Write the equations for: (i) Clemmensen reduction of propanone (ii) Wolff-Kishner reduction of acetophenone (iii) the iodoform reaction of ethanal.Unit VIII How will you prepare: (i) benzoic acid from propylbenzene (ii) butanoic acid from 1-bromopropane (iii) ethanoic acid from ethanenitrile? Write the equations.Unit VIII Write the main organic product: (i) CH₃CH₂COOH treated with Br₂ and red phosphorus (ii) C₆H₅COOH treated with SOCl₂ (iii) CH₃COONa heated with NaOH and CaO.Unit VIII Describe the Hinsberg test for distinguishing primary, secondary and tertiary amines, with equations.Unit IX Write the reactions of benzenediazonium chloride with: (i) CuBr and HBr (ii) HBF₄, followed by heating (iii) aniline in a mildly acidic medium.Unit IX Account for: (i) aniline is a weaker base than ammonia (ii) lower aliphatic amines dissolve in water, but solubility falls as the chain grows (iii) N-ethylethanamine boils higher than N,N-dimethylethanamine, though both have molar mass 73.Unit IX How will you convert: (i) benzamide into aniline (ii) aniline into iodobenzene (iii) aniline into p-nitroaniline?Unit IX Give three facts about glucose that the open-chain structure cannot explain. How does the cyclic structure account for them?Unit X What are essential amino acids? Explain why amino acids are amphoteric, using the zwitterion of glycine.Unit X Write the products of hydrolysis of sucrose, maltose and lactose. Which of them shows inversion, and why?Unit X

5 marks · long answer

(a) Define osmotic pressure. Why is it the best colligative property for finding the molar mass of proteins and polymers? (b) Calculate the osmotic pressure at 300 K of a solution containing 1.8 g of glucose (M = 180 g mol⁻¹) in 100 mL of solution (R = 0.083 L bar mol⁻¹ K⁻¹). (c) What happens to red blood cells placed in 2% NaCl solution, and why?Unit I (a) Distinguish between ideal and non-ideal solutions. (b) Explain positive and negative deviations from Raoult's law, with one example and a labelled graph for each. (c) What is a maximum boiling azeotrope? Give one example.Unit I (a) State Kohlrausch's law of independent migration of ions and explain how it helps to find Λ°m of a weak electrolyte. (b) Draw and explain the graphs of Λm against √c for KCl and CH₃COOH. (c) Why does the conductivity of a solution fall on dilution?Unit II (a) Describe the standard hydrogen electrode with a labelled diagram. (b) Write the Nernst equation for the cell Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s) and calculate its EMF at 298 K when [Zn²⁺] = 0.001 M and [Cu²⁺] = 0.1 M. (E°cell = 1.10 V) (c) How does the EMF change if [Cu²⁺] is lowered?Unit II (a) Derive the integrated rate equation for a first order reaction. (b) For A(g) → B(g) + C(g), the initial pressure is 0.40 atm and the total pressure after 100 s is 0.70 atm. Find k. (log 4 = 0.6020) (c) Draw the plot of ln[R] against t.Unit III (a) Write the Arrhenius equation and explain each term. (b) Draw the distribution of kinetic energies of molecules at T and T + 10 and use it to explain why the rate nearly doubles. (c) How is Ea found from a plot of ln k against 1/T?Unit III (a) Describe the preparation of potassium dichromate from chromite ore, with balanced equations. (b) What colour change is seen when an alkali is added to K₂Cr₂O₇ solution, and why? (c) Write ionic equations for the oxidation of iodide ions and of H₂S by acidified dichromate.Unit IV (a) How is KMnO₄ prepared from pyrolusite? Write equations. (b) Write balanced ionic equations for the reaction of KMnO₄ with oxalate ions and with Fe²⁺ ions in acid. (c) Why is KMnO₄ called a self-indicator?Unit IV (a) Using valence bond theory, explain the hybridisation, shape and magnetic behaviour of [Fe(CN)₆]³⁻ and [FeF₆]³⁻. (b) Calculate the spin-only magnetic moment of each. (c) Write two limitations of valence bond theory.Unit V (a) Explain crystal field splitting in an octahedral complex with a labelled diagram. (b) Why is [Ti(H₂O)₆]³⁺ violet, while anhydrous CuSO₄ is white? (c) Arrange H₂O, CN⁻, Cl⁻ and NH₃ in increasing order of crystal field splitting. (d) Why are tetrahedral complexes nearly always high spin?Unit V (a) Explain the SN1 mechanism with an example, and give its rate law. (b) Arrange in increasing order of reactivity towards SN2: CH₃CH₂Br, (CH₃)₃CBr, CH₃Br, (CH₃)₂CHBr. (c) Bromoethane gives different products with KCN and with AgCN. Name both and explain the difference.Unit VI (a) Write equations for the conversion of chlorobenzene into phenol, the Wurtz-Fittig reaction and the Fittig reaction. (b) Chlorine deactivates the benzene ring but directs incoming groups to ortho and para positions. Explain. (c) Name the major product of the nitration of chlorobenzene.Unit VI (a) Write the mechanism of the formation of ethoxyethane from ethanol. (b) Why is 2-methoxy-2-methylpropane made from sodium tert-butoxide and bromomethane, and not from 2-bromo-2-methylpropane and sodium methoxide? (c) Write the equation for the bromination of anisole in ethanoic acid.Unit VII (a) Explain, with resonance structures, why phenol is more acidic than ethanol. (b) Arrange in increasing order of acid strength, with reasons: ethanol, phenol, p-nitrophenol, p-cresol. (c) What is acetylation? Write the equation for the preparation of aspirin.Unit VII (a) Write the mechanism of addition of HCN to a carbonyl compound, and say why a little base speeds it up. (b) Arrange pentan-3-one, ethanal, methanal and propanone in increasing order of reactivity towards HCN, giving reasons. (c) Write the products of ethanal with hydroxylamine and with semicarbazide.Unit VIII Compound A (C₃H₆O) does not reduce Tollens' reagent but gives a yellow precipitate with iodine and NaOH. A is reduced by NaBH₄ to B, which on heating with an acid gives C (C₃H₆). With dilute Ba(OH)₂, A gives D (C₆H₁₂O₂), which loses water on heating. Identify A, B, C and D, and write all the equations.Unit VIII (a) Write the Gabriel phthalimide synthesis of a primary amine, and state its main limitation. (b) Write the Hoffmann bromamide degradation of benzamide. (c) How is aniline prepared from nitrobenzene, and why is scrap iron with HCl preferred?Unit IX (a) How is benzenediazonium chloride prepared, and why must it be kept cold? (b) Write equations for its conversion into chlorobenzene, iodobenzene, phenol and benzene. (c) Write one coupling reaction and name the product.Unit IX (a) Describe the primary, secondary, tertiary and quaternary structures of proteins and the forces that hold each. (b) Distinguish between fibrous and globular proteins, with an example of each. (c) What is denaturation? Give two examples.Unit X (a) Describe the composition of nucleic acids and the double-helix structure of DNA. (b) Give three differences between DNA and RNA. (c) A DNA sample contains 22% thymine. Find the percentage of each of the other bases.Unit X

4 marks · case-based

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