CBSE Class 12 Chemistry Guess Paper 2027

In the ring structure of fructose, the anomeric carbon is : (A) C2 (B) C3 (C) C4 (D) C1

[Case context: Carbohydrates are optically active polyhydroxy aldehydes or ketones or molecules that provide such units on hydrolysis. They are broadly classified into three groups : monosaccharides, oligosaccharides and polysaccharides. Monosaccharide units are held together by glycosidic linkages to form disaccharides or polysaccharides. Starch and cellulose are polysaccharides. Starch is a polymer of alpha-glucose and consists of two components : Amylose and Amylopectin. Amylose is water soluble, having 15-20% of starch, whereas Amylopectin is insoluble in water, having 80-85% starch. Chemically, amylose is a long unbranched chain of alpha-glucose units held together by C1-C4 glycosidic linkage. Amylopectin is a branched chain of alpha-glucose units held together by C1-C4 and C1-C6 glycosidic linkages.] Write two differences between Amylose and Amylopectin.

Write the formula of the following coordination complex: I. diaquasilver(I) dichloridoargentate(I) II. dihydroxidobis(triphenylphosphine)nickel(II)

Which of the following elements will: I. exhibit similar magnetic behaviour and why? Magnesium (Atomic No. 12), Chromium (Atomic No. 24), Iron (Atomic No. 26) and Molybdenum (Atomic No. 42). II. form white salts and why? Zinc (Atomic No. 30), Scandium (Atomic No. 21), Nickel (Atomic No. 28) and Vanadium (Atomic No. 23)

The organic compounds A, B and C are amines having equivalent molecular weight. A and B on reaction with benzene sulphonyl chloride give white precipitate, however white precipitate obtained from compound B remains insoluble in NaOH. The variation in the boiling point of A, B and C can be seen as : A. A> B>C B. B>A>C C. A=B > C D. C>B>A

Assertion (A) : p-nitrophenol is less acidic than phenol. Reason (R) : Nitro group is an electron-withdrawing group, which stabilises the phenoxide ion.

Acetamide reacts with Br₂ and aqueous KOH to form : (A) Ethanamine (B) Ammonia (C) Methanamine (D) Ethanenitrile

Arrange the following compounds in increasing order of their boiling points: (i) (CH₃)₂CH-CH₂Br (ii) CH₃CH₂CH₂CH₂Br (iii) (CH₃)₃C-Br The correct order is (A) (ii) < (i) < (iii) (B) (i) < (ii) < (iii) (C) (iii) < (i) < (ii) (D) (iii) < (ii) < (i)

The name inner transition metals is often used to refer to the A. lanthanoids B. actinoids C. both lanthanoids and actinoids D. d block elements

For an electrolyte consisting of a monovalent cation and a monovalent anion undergoing dissociation in water, the van't Hoff factor (i) is : (A) less than 1 (B) equal to 1 (C) greater than 1 (D) greater than 2

Calculate the molarity and molality of a KI solution if the density of 20% (mass/mass) aqueous solution of KI is 1.2 g mL^-1. [Given : Molar mass of KI = 166 g mol^-1]

Write two differences between S_N1 and S_N2 reactions. Out of chlorobenzene and 2,4,6-trinitrochlorobenzene, which one is more reactive towards nucleophilic substitution reactions ?

Formulation of Cobalt(III) Chloride-Ammonia Complexes: Colour / Formula / Solution conductivity corresponds to Yellow / [Co(NH₃)₆]³⁺ 3Cl^- / Y Purple / [CoCl(NH₃)₅]²⁺ 2Cl^- / 1:2 electrolyte Green / X / 1:1 electrolyte 'X' and 'Y' in the above table are: a. X=[Co(NH₃)₆]²⁺ 3Cl^-, Y= 1:3 b. X= [Co(NH₃)₄Cl₂]^+ Cl^-, Y= 1:3 c. X=[Co(NH₃)₄Cl₂]^+ Cl^-, Y= 1:1 d. X=[Co(NH₃)₄Cl₂]³⁺ 3Cl^-, Y= 1:1

Which of the following will give a yellow or orange ppt. with 2,4 DNP? (i) Porpanal (ii) Propanone (iii) Propanoic acid A. (i) and (ii) B. (ii) and (iii) C. (i) and (iii) D. (i), (ii) and (iii)

Arrange the products obtained in the following cases in the increasing order of their pKa values: A. Oxidation of ethanol in presence of acidified potassium dichromate B. Reaction of propanoic acid with Br₂ in the presence of red Phosphorus C. Reaction of isopropyl magnesium bromide with carbon dioxide, followed by hydrolysis. D. Reaction of propanoic acid with Cl₂ in the presence of red Phosphorous.

[Case context: passage on boiling points of alcohols and phenols increasing with number of carbon atoms and intermolecular hydrogen bonding.] Arrange the following compounds in order of their increasing boiling points : Propan-1-ol, Ethanol, Butan-2-ol, Butan-1-ol

Write the reactions involved when D-glucose is treated with the following reagents: (a) HCN (b) Br₂ water

Define the following terms : (a) Ambidentate ligand (b) Crystal field splitting energy

[case context: Conductivity of Aqueous Solutions - conductivity meter readings for two solutions A (Red LED bright, Green LED dim) and B (Red LED dim, Green LED off).] Refer to the table given below and draw the molar conductivity vs. concentration curve for solution A and B.

Write the Nernst equation for the following: I. Ni (s) + Cu²⁺ (aq) -> Ni²⁺ (aq) + Cu (s) II. Al (s) + FeSO₄ (aq) -> Al₂(SO₄)₃ (aq) + Fe (s) III. Mg (s)/Mg²⁺ (aq)//Ag^+ (aq)/Ag(s)

Complete the following reactions by writing the major and minor product in each case (any 2) a. CH₃CH₂Br + KCN -> b. CH₃CH₂CH = CH₂ + HBr -> c. (CH₃)₂CHCHClCH₃ + alc KOH ->

The elements of 3d transition series are given as: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn. Answer the following: (a) Copper has exceptionally positive E°_M²⁺/M value, why? (b) Which element is a strong reducing agent in +2 oxidation state and why? (c) Zn²⁺ salts are colourless. Why?

Attempt either A or B. A. Answer the following questions: I. Identify and give any one point of difference between the protein present in the hair and protein present in egg albumin. II. Both glucose and sucrose have aldehydic group, then why does only glucose reduces Fehling's Reagent and not sucrose? III. Why do amino acids behave as salts? IV. What chemical change takes place during curdling of milk? V. Doctor advised a 50 year old woman enough exposure to sunlight and addition of fish and egg yolk to her diet. What is the possible disease diagnosed by the doctor?

(i) Write the hybridisation and magnetic behaviour of the following complexes : (I) [Ni(CN)₄]^2- (II) [FeF₆]^3- (ii) What type of isomerism is shown by [Co(NH₃)₅(NO₂)]²⁺ and [Co(NH₃)₅(ONO)]²⁺ ? [Given : Atomic number : Ni = 28, Fe = 26]

(i) The cell in which the following reaction occurs : 2Fe³⁺ (aq) + 2I^- (aq) -> 2Fe²⁺ (aq) + I₂ (s) has E^o_(cell) = 0.24 V at 298 K. Calculate delta_rG^o and log K_C of the cell reaction. [Given : 1 F = 96500 C mol^-1] (ii) State the following laws : (I) Faraday's first law of electrolysis (II) Kohlrausch's law of independent migration of ions

Attempt either A or B. A. I. The rate of a reaction triples when the temperature changes from 298 K to 318 K. Calculate the energy of activation of the reaction assuming that it does not change with temperature. (Given R = 8.314 JK^-1mol^-1, log 3 = 0.4771) II. Identify the order of reaction and write its integrated rate equation mentioning what each term in the equation represents. (graph of concentration of R vs time, a straight line with k = -slope)

Answer the following questions: I. Are the enthalpies of atomisation of Zinc and Copper matched correctly? Justify your answer. (Enthalpy of atomisation / kJmol^-1: Zinc 339, Copper 130) II. Out of sulphuric acid and hydrochloric acid, which acid will you prefer for permanganate titrations and why? III. 5NO₂^- + 2MnO₄^- + 6H^+ -> (complete the equation)

OR An organic compound 'X', does not undergo aldol condensation. However 'X' with compound 'Y' in the presence of a strong base react to give the compound 1,3-diphenylprop-2-en-1-one. a. Identify 'X' and 'Y' b. Write the chemical reaction involved. c. Give one chemical test to distinguish between X and Y.

[case context: Amines are basic; pK_b measures basic strength (lower pK_b = more basic). Effect of substituent X on basic strength was studied by replacing the -CH_2- group in piperidine (compound 1) and in propylamine CH₃CH₂CH₂NH₂ (compound 2). Data (X: electronegativity, pK_a of substituted piperidine / pK_a of substituted propylamine): CH₂ 2.55, 11.13/10.67; NH 3.12, 9.81/10.08; O 3.44, 8.36/9.45; CH₃CON 3.6, 7.94/9.28; C₆H₅CON 3.7, 7.78/—. (source: Hall Jr, 1956)] a. Plot a graph between the electronegativity of the substituent vs pK_b value of the corresponding substituted propyl amine (given that pK_a + pK_b = 14). Is there any relation between the electronegativity of the substituent and its basic strength?

Assertion (A): [Mn(CN)₆]^3- has a magnetic moment of two unpaired electrons while [MnCl₆]^3- has a paramagnetic moment of four unpaired electrons. Reason (R): [Mn(CN)₆]^3- is inner orbital complexes involving d²sp³ hybridisation, on the other hand, [MnCl₆]^3- is outer orbital complexes involving sp³d² hybridisation. Select the most appropriate answer from the options given below: 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.

Attempt either A or B. A. Answer the following questions: I. Write the structure of expected product of Cannizzaro reaction of 2-chlorobenzaldehyde. II. How would the presence of -SO₃H group effect the basic strength of aniline. III. Convert acetic acid to ethanamine. IV. Write the steps to prepare Benzoic acid from Benzoyl chloride. V. Give a chemical test to distinguish between: propanal and propanone

(i) Write the Nernst equation and calculate the emf of the following cell at 298 K : Mg (s) | Mg²⁺ (0.001 M) || Cu²⁺ (0.0001 M) | Cu (s) Given : E^o_Mg²⁺/Mg = - 2.36 V, E^o_Cu²⁺/Cu = + 0.34 V [log 10 = 1] (ii) Define fuel cell and write its two advantages.

Give reasons : (i) Why are low spin tetrahedral complexes not formed ? (ii) Why is [Co(en)₃]³⁺ complex more stable than [Co(NH₃)₆]³⁺ ? (iii) Why are geometrical isomers not possible for tetrahedral complexes having two different types of unidentate ligands coordinated to the central metal ion ?