ISC Class 12 Chemistry Guess Paper 2027

Crystal field splitting energy (CFSE) for high spin d⁴ octahedral complex is: (a) -1.6 Delta_o (b) -1.2 Delta_o (c) -0.8 Delta_o (d) -0.6 Delta_o

Data for hypothetical reaction 2A + B -> 2AB: Exp 1: [A]=0.5, [B]=0.5, rate=1.8x10^-4; Exp 2: [A]=1.0, [B]=0.5, rate=3.6x10^-4; Exp 3: [A]=1.0, [B]=1.0, rate=3.6x10^-4 (mol L^-1 sec^-1). The rate law expression is: (a) rate=k[A]¹[B]¹ (b) rate=k[A]¹[B]⁰ (c) rate=k[A]²[B]¹ (d) rate=k[A]⁰[B]¹

The correct order of freezing point of 0.5 M solution of urea, AlCl₃, KCl and MgCl₂ is: (a) AlCl₃ > MgCl₂ > KCl > urea (b) Urea > KCl > MgCl₂ > AlCl₃ (c) MgCl₂ > KCl > AlCl₃ > urea (d) KCl > MgCl₂ > AlCl₃ > urea

The sum of coordination number and oxidation number of metal 'M' in the complex [M(en)₂Cl₂] is: (a) 6 (b) 8 (c) 9 (d) 10

Which of the following reactions will NOT give primary amine? (a) C₂H₅NC --LiAlH_4--> (b) C₂H₅CN --LiAlH_4--> (c) C₂H₅CONH₂ --Br₂/KOH--> (d) CH₃CONH₂ --Br₂/KOH-->

Cobalt (III) chloride forms several octahedral complexes with ammonia. Which will NOT give a test for chloride ions with silver nitrate solution at 25 degC? (a) CoCl₃.6NH₃ (b) CoCl₃.5NH₃ (c) CoCl₃.4NH₃ (d) CoCl₃.3NH₃

[context: The boiling points of alcohols are higher than those of corresponding ethers due to intermolecular hydrogen bonding and increase with molecular mass; for isomeric alcohols the order is 1 deg > 2 deg > 3 deg: Propan-1-ol 370 K, Butan-1-ol 391 K, Butan-2-ol 371 K, 2-methyl-propan-2-ol 356 K. Aliphatic alcohols are weak acids, weaker than water and phenol. Phenols are used both as a disinfectant and an antiseptic at different concentrations.] Although alcohols are weaker acids than water, phenol is more acidic than alcohols. Justify.

[context: Vishal measured the resistance of aqueous KCl solutions at 298 K using a conductivity cell connected to a Wheatstone bridge and recorded: 1.00 M: kappa = 111.3 x 10^-3 S cm^-1, Lambda_m = 111.3 S cm² mol^-1; 0.10 M: kappa = 12.9 x 10^-3, Lambda_m = 129.0; 0.01 M: kappa = 1.41 x 10^-3, Lambda_m = 141.0] Why did the molar conductivity increase though the conductivity decreased with dilution?

Fill in the blanks by choosing the appropriate word(s) from those given in the brackets: [methyl alcohol, ethyl alcohol, paired, one, Cannizzaro, d-d, salicylaldehyde, Perkin's, unpaired, f-f, salicylic acid, Kolbe's, two, 193000, 96500, Reimer-Tiemann] Formaldehyde reacts with conc. alkali to give sodium formate and ______ due to the absence of alpha-hydrogen atom. The reaction is known as ______ reaction.

[context: Living beings maintain a balance of radioactive C-14 in their tissues (formed in the upper atmosphere: ₇N¹⁴ + ₀n¹ -> ₆C¹⁴ + ₁H¹; ratio C-14 : C-12 = 1 : 10¹²). After death C-14 decays (₆C¹⁴ -> ₇N¹⁴ + _-1e⁰ + gamma rays) and is not replaced. The half-life of C-14 is 5770 years, so the age of a fossil can be determined.] The half-life period (t_1/2) for a first order reaction is 30 minutes. Calculate the time taken to complete 87.5% of the reaction.

Fill in the blanks by choosing the appropriate word(s) from those given in the brackets: [first, alc. AgCN, primary, decrease, third, increase, zero, Lucas, alc. KCN, KOH, no change, two, Tollen's, AgOH, tertiary] Methyl chloride on treatment with ______ forms methyl cyanide, whereas on treatment with ______ it forms methyl isocyanide.

[context: Kohlrausch observed that different pairs of strong electrolytes having a common cation or anion had almost the same difference of Lambda^inf_m, and postulated the Law of Independent Migration of ions. Molar conductivities at infinite dilution lambda^inf_m (S cm² mol^-1): Ba²⁺ 127.2, Cl^- 76.3, Ca²⁺ 119.0, SO₄^2- 160.0] Calculate the molar conductance at infinite dilution Lambda^inf_m for BaCl₂.

[context: During an unexpected heavy snowfall in Kashmir, thousands of visitors were stranded because it was dangerous to travel on snowy roads and vehicles could not move as water froze in the car radiators. Officials decided to sprinkle rock salt or CaCl₂ on the roads.] How many grams of ethylene glycol (mol. wt. = 62 g mol^-1) should be added to 10 kg of water so that the solution freezes at -10 degC? (K_f for water = 1.86 K kg mol^-1)

Fill in the blanks by choosing the appropriate word(s) from those given in the brackets: [methyl alcohol, ethyl alcohol, paired, one, Cannizzaro, d-d, salicylaldehyde, Perkin's, unpaired, f-f, salicylic acid, Kolbe's, two, 193000, 96500, Reimer-Tiemann] The colour of transition metal ions is due to ______ electron(s) in d-subshell and ______ transition.

(i) Why is the first ionisation enthalpy of chromium less than that of zinc? (Atomic Number Cr=24, Zn=30) (ii) Why does pink colour of aqueous KMnO₄ solution disappear when warmed with oxalic acid solution in acidic medium?

Answer the following with respect to the coordination complex ion [Cr(NH₃)₆]³⁺: (a) What is the hybridisation state of the central metal atom? (b) Comment on the magnetic nature of the complex ion.

An organic compound [A] with molecular formula C₃H₇NO forms compound [B] on heating with Br₂ and KOH. Compound [B] on heating with CHCl₃ and alcoholic KOH produces a pungent smelling compound [C]. Compound [B] on reacting with C₆H₅SO₂Cl forms compound [D] which is soluble in alkali. Write the structures of compounds [A], [B], [C] and [D].

An organic compound 'X' with molecular formula C₄H₁₀O is soluble in conc. H₂SO₄ and does not react with sodium metal or KMnO₄. Compound 'X' when heated with excess of HI gives a single alkyl halide. Deduce the structure of 'X'. Explain all the reactions involved.

Write chemical equations to convert each of the following: (i) Methyl magnesium bromide to propan-2-ol (ii) Phenol to benzene

Calculate the value of E^o_cell, E_cell and DeltaG that can be obtained from the following cell at 298 K. Al / Al³⁺(0.01M) // Sn²⁺(0.015M) / Sn. Given E^o_Al³⁺/Al = -1.66 V, E^o_Sn²⁺/Sn = -0.14 V.

Account for each of the following: (i) Zirconium (Zr) and Hafnium (Hf) are difficult to separate. (ii) Salts of Cupric (Cu²⁺) ion are coloured whereas salts of Cuprous (Cu^+) ion are colourless.

In general, the rate of a reaction becomes double with every 10 degC rise in temperature. If this generalisation holds true, calculate the value of activation energy when temperature changes from 295 K to 305 K.

Write the Nernst equation and calculate the emf of the following cell at 298 K: Mg(s) / Mg²⁺(1x10^-3M) // Cu²⁺(1x10^-4M) / Cu(s). Given E^o_Mg²⁺/Mg = -2.373 V, E^o_Cu²⁺/Cu = +0.337 V.

When 2 g of benzoic acid (C₆H₅COOH) is dissolved in 25 g of benzene, it shows a depression in freezing point equal to 1.62 K. Molal depression constant for benzene is 4.7 K kg mol^-1. What is the percentage association of acid if it forms dimer in solution?

(i) Identify the non-reducing sugar which on hydrolysis gives two reducing monosaccharides. (ii) Which structure of protein is normally unaffected during denaturation of protein? (iii) Name the vitamins whose deficiency cause the following diseases: (a) Rickets (b) Night blindness

Write the chemical equations for the following conversions: (i) Nitrobenzene to benzene (ii) Aniline to bromobenzene (iii) Methyl cyanide to ethylamine

Write chemical equations to illustrate the following name reactions: (i) Rosenmund's reaction (ii) Benzoin condensation (iii) Perkin's reaction

(i) The unit of rate constant of a reaction is same as that of its rate of reaction. Find the order of this reaction. (ii) Give one example of pseudo first order reaction. (iii) How will the rate of reaction be affected when the surface area of the reactant is reduced?

How will the following be obtained? (Give chemical equation) (a) Picric acid from Phenol (b) Ethyl acetate from ethanol (c) Anisole from sodium phenoxide

Give a chemical test to distinguish between the following pairs of compounds: (a) Ethanol and methanol (b) Ethanol and Ethanal (c) Propan-2-ol and 2-methyl propan-2-ol

(a) The molar conductivity at infinite dilution for lambda^inf_H^+ = 348.65 S cm² mol^-1 and lambda^inf_CH3COO^- = 41.4 S cm² mol^-1. Calculate the degree of dissociation (alpha) of acetic acid if its molar conductivity (Lambda^c_m) is 40.65 S cm² mol^-1. (b) Compounds [A] and [B] are two electrolytes. Upon dilution, the molar conductivity of [A] increases 3 times while that of [B] increases 30 times. Which one is a weak electrolyte? Why? (c) Can copper sulphate solution be stored in a zinc pot? Give a reason (E⁰_Zn²⁺/Zn=-0.76 V, E⁰_Cu²⁺/Cu=+0.34 V).

(i) The resistance of a conductivity cell with 0.1 M KCl solution is 200 ohm. When the same cell is filled with 0.02 M NaCl solution, the resistance is 1100 ohm. If the conductivity of 0.1 M KCl solution is 0.0129 ohm^-1cm^-1, calculate the cell constant and molar conductivity of 0.02 M NaCl solution. (ii) The emf (E⁰_cell) of the following reaction is 0.89 V: 3Sn⁴⁺ + 2Cr -> 3Sn²⁺ + 2Cr³⁺. Calculate the value of DeltaG⁰ for the reaction. Predict whether the above reaction will be spontaneous or not.

(i) The compound [PtCl₂(NH₃)₂] known as cis-platin is used in chemotherapy. (a) Write its IUPAC name and the type of isomerism it exhibits. (b) What is the geometry of the compound? (ii) What type of structural isomers are [Pt(NH₃)₃Br]NO₃ and [Pt(NH₃)₃(NO₃)]Br? How can they be distinguished by a chemical test? (iii) A coordination compound CoCl₃.4H₂O precipitates silver chloride when treated with silver nitrate. The molar conductance of its solution corresponds to a total of two ions. Write the structural formula of the compound and name it.

An organic compound [A] (C₂Cl₃O₂H) is obtained when compound [B] reacts with red phosphorous and Cl₂. [B] can be obtained on reaction of methyl magnesium bromide with carbon dioxide followed by acid hydrolysis. Upon partial reduction, [B] forms [C] (C₂H₄O) which gives yellow precipitate of iodoform on heating with iodine and sodium hydroxide. [C] also reacts with dilute NaOH to form [D]. (a) Identify [A], [B], [C] and [D]. (b) Write the reaction for formation of [A] from [B]. What is the reaction called? (c) Write the chemical test to distinguish between [C] and acetone. (d) Which will be more acidic, [A] or [B]? Why?