CBSE Class 12 Chemistry Question Paper 2023

Here in this post we are giving the latest 2023 Chemistry Question Paper for CBSE Class 12 Students. This Question paper will be helpful for the next year Class 12 aspirants. This also help the new class students to understand the question pattern for the next CBSE Class 12 Chemistry Examination. We hope this post will helpful for every one.

Chemistry Question Paper 2023 Class 12

SECTION – (A)

(1) Which one of the following has lowest pK, value?

(a) CH3-COOH

(b) O₂N-CH2-COOH

(d) HCOOH

(2) Which of the following cell was used in Apollo space programme?

(a) Mercury cell

(b) Daniel cell

(d) Dry cell

(3) Consider the following standard electrode potential values:

Fe3 + (aq) + e → Fe2+(aq) E° = +0.77 V

Consider the following standard electrode potential values:

Fe3 + (aq) + e → Fe2 + (aq) E° = +0.77 V

MnO4 (aq) + 8H+ + 5e → Mn2 + (aq) + 4 H₂O(l) E° = +1.51 V

What is the cell potential for the redox reaction?

(a) -2.28 V

(b) -0.74 V

(d) + 2.28 V

(4) The following experimental rate data were obtained for a reaction carried out at 25 °C:

A + B + C + D(g)

Initial [AJ/mol dm-3

3.0 x 10-2

6.0 × 10-2

Initial [BJ/mol dm-3

2.0 × 10-2

4.0 × 10-2

Initial rate/mol dm-3g1

1.89 × 10-4

7.56 × 10-4

What are the orders with respect to A) and By?

What are the orders with respect to A(g) and B(g)?

Order with respect to A(g)

(a) Zero

(b) First

(d) Second

Order with respect to B(g)

(a) Second

(b) Zero

(d) First

(5) The magnetic moment of [NiCIMSUS

(a) 1.82 BM

(b) 2.82 BM

(d) 5.46 BM

[Atomic number : Ni = 28]

(6) Which of the following ions has the electronic configuration 3d6? (Atomic number : Mn = 25, Co = 27, Ni = 28)

(a) Ni3+

(b) Co³+

(d) Mn3+

(7) Which of the following aqueous solution will have highest boiling point?

(a) 1.0 M KCI

(b) 1.0 M K₂SO

(d) 2.0 M K₂SO4

(8) A voltaic cell is made by connecting two half cells represented by half equations below:

Sn2+ (aq) + 2e -> Sn) E = -0.14 V

Fe3+ (aq) + e Fe2+ (aq) E° = +0.77 V

Which statement is correct about this voltaic cell?

(a) Fe2+ is oxidised and the voltage of the cell is -0.91 V.

(b) Sn is oxidised and the voltage of the cell is 0.91 V.

(d) Sn is oxidised and the voltage of the cell is 0.63 V.

(9) Amides can be converted into amines by the reaction named

(a) Hoffmann degradation

(b) Ammonolysis

(d) Diazotisation

(10) Which of the following statements is not true about glucose?

(a) It is an aldohexose.

(b) On heating with HI it forms n-hexane.

(d) It gives 2, 4 DNP test

(11) Which of the following alcohols will not undergo oxidation?

(a) Butanol

(b) Butan-2-ol

(d) 3-Methylbutan-2-ol

(12) Four half reactions I to IV are shown below:

I. 2C → Cl₂+ 2e

II. 40H- → 02, + 2H2O + 2e-

III. Na + e- → Na

IV. 2H+ + 2e- → H₂

Which two of these reactions are most likely to occur when concentrated brine is electrolysed?

(a) I and III

(b) I and IV

(d) II and IV

(13) Which property of transition metals enables them to behave as catalysts?

(a) High melting point

(b) High ionisation enthalpy

(d) Variable oxidation states

(14) Which of the following would not be a good choice for reducing nitrobenzene to aniline?

(a) LiA/H

(b) H/Ni

(d) Sn and HCI

For questions number 15 to 18, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

(d) Assertion (A) is false, but Reason (R) is true.

(15) Assertion (A): Vitamin C cannot be stored in our body.

Reason (R): Vitamin C is fat soluble and is excreted from the body in urine.

(16) Assertion (A): The half life of a reaction is the time in which the concentration of the reactant is reduced to one half of its initial concentration.

Reason (R): In first order kinetics when concentration of reactant is doubled, its half life is doubled.

(17) Assertion (A): Bromination of benzoic acid gives m-bromobenzoic acid. Reason (R): Carboxyl group increases the electron density at the meta position.

(18) Assertion (A): EDTA is a hexadentate ligand. Reason (R): EDTA has 2 nitrogen and 4 oxygen donor atoms.

SECTION – B

(19) – (a) Which of the following species cannot act as a ligand? Give reason.

OH-, NH+4, CH3NH2, H2O

(b) The complex [Co(NH3)5(NO2)]Cl2 is red in colour. Give IUPAC name of its linkage isomer.

(20) For the pair phenol and cyclohexanol, answer the following:

(a) Why is phenol more acidic than cyclohexanol?

(b) Give one chemical test to distinguish between the two.

(21) (a) – (i) Draw the zwitter ion structure for sulphanilic acid.

(ii) How can the activating effect of -NH, group in aniline be controlled?

(b) (i) Complete the reaction with the main product formed:

(ii) Convert Bromoethane to Propanamine.

(22) Write equations for the following:

(a) Oxidation of chloroform by air and light

(b) Reaction of chlorobenzene with CH,CI/ anhyd. AICI,

(23) What happens to the rate constant k and activation energy E, as the temperature of a chemical reaction is increased? Justify.

(24) (a) – (i) What should be the signs (positive/negative) for Ec and AG° Cell for a spontaneous redox reaction occurring under standard conditions?

(ii) State Faraday’s first law of electrolysis.

(b) Calculate the emf of the following cell at 298 K: Fe) Fe2+ (0.01M) || Ha Given E Cell = 0.44V. (1M) H2(g) (1 bar), Pt()

(25) Give the reaction of glucose with acetic anhydride. Presence of which group is confirmed by this reaction?

SECTION – (C)

(26) (a) – (i) Why is the C – O bond length in phenols less than that in methanol?

(ii) Arrange the following in order of increasing boiling point:

Ethoxyethane, Butanal, Butanol, n-butane

(iii) How can phenol be prepared from anisole ? Give reaction.

(b) – (i) Give mechanism of the following reaction :

CH3CH2OH H2SO4/413 K -> CH3CH2 – O – CH2CH3 + H2O

(ii) Illustrate hydroboration-oxidation reaction with an example.

(27) – (a) On the basis of crystal field theory write the electronic configuration for do ion with a weak ligand for which Δ0 < P.

(b) Explain [Fe(CN)6]3- is an inner orbital complex whereas

[FeF6]3- is an outer orbital complex.

[Atomic number: Fe = 26]

(28) Give reasons for any 3 of the following observations:

(a) Penta-acetate of glucose does not react with hydroxylamine.

(b) Amino acids behave like salts.

(d) The two strands in DNA are complimentary to each other.

(29) (a) For the reaction

2N205(g) → 4NO2(g) + O2(g) at 318 K

Calculate the rate of reaction if rate of disappearance of N2O5(g) is 1.4 x 10-3 m s-1.

(b) For a first order reaction derive the relationship t99% = 2t90%

(30) – (a) Illustrate Sandmeyer’s reaction with an equation.

(b) Explain, why (CH3)2NH is more basic than (CH3)3N in aqueous solution.

SECTION – (D)

The following questions are case-based questions. Read the passage carefully and answer the questions that follow:

(31) Rahul set-up an experiment to find resistance of aqueous KCl solution for different concentrations at 298 K using a conductivity cell connected to a Wheatstone bridge. He fed the Wheatstone bridge with a.c. power in the audio frequency range 550 to 5000 cycles per second. Once the resistance was calculated from null point he also calculated the conductivity K and molar conductivity ^m and recorded his readings in tabular form.

S.No.	Conc.(M)	k S cm-1	^m S cm² mol-1
1.	1.00	111.3 x 10-3	111.3
2.	0.10	12.9 x 10-3	129.0
3.	0.01	1.41 x 10-3	141.0

Answer the following questions :

(a) Why does conductivity decrease with dilution?

(b) If ^m° of KCl is 150.0 S cm² mol-1, calculate the degree of dissociation of 0.01 M KCI.

(c) If Rahul had used HCl instead to KCI then would you expect the m values to be more or less than those per KCI for a given concentration. Justify.

Amit a classmate of Rahul repeated the same experiment with CH,COOH solution instead of KCl solution. Give one point that would be similar and one that would be different in his observations as compared to Rahul.

(32) Nucleophilic Substitution

Nucleophilic Substitution reaction of haloalkane can be conducted according to both S1 and S2 mechanisms. S1 is a two step reaction while S2 is a single step reaction. For any haloalkane which mechanism is followed depends on factors such as structure of haloalkane, properties of leaving group, nucleophilic reagent and solvent.

Influences of solvent polarity: In S1 reaction, the polarity of the system A increases from the reactant to the transition state, because a polar solvent has a greater effect on the transition state than the reactant, thereby reducing activation energy and accelerating the reaction. In SN2 reaction, the polarity of the system generally does not change from the reactant to the transition state and only charge dispersion occurs. At this time, polar solvent has a great stabilizing effect on Nu than the transition state, thereby increasing activation energy and slow down the reaction rate. For example, the decomposition rate (S1) of tertiary chlorobutane at 25 °C in water (dielectric constant 79) is 300000 times faster than in ethanol (dielectric constant 24). The reaction rate (S2) of 2-Bromopropane and NaOH in ethanol containing 40% water is twice slower than in absolute ethanol. Hence the level of solvent polarity has influence on both S1 and SN2 reaction, but with different results. Generally speaking weak polar solvent is favourable for S2 reaction, while strong polar solvent is favourable for S1. Generally speaking the substitution reaction of tertiary haloalkane is based on Sl mechanism in solvents with a strong polarity (for example ethanol containing water)

Answer the following questions:

(a) Why racemisation occurs in SN1?

(b) Why is ethanol less polar than water?

(i) CH3-CH2-I or CH3CH2 – Cl

(ii) Cl or CH2 – CI

(1) 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane

(ii) 1-Bromo-3-methylbutane, 2-Bromo-2-methylbutane, 2-Bromo-3-methylbutane

SECTION-E

(33) – (a) (i) Write the reaction involved in Cannizaro’s reaction.

(ii) Why are the boiling point of aldehydes and ketones lower than that of corresponding carboxylic acids ?

(iii) An organic compound ‘A’ with molecular formula C5H8O2 is reduced to n-pentane with hydrazine followed by heating with NaOH and Glycol. ‘A’ forms a dioxime with hydroxylamine and gives a positive Iodoform and Tollen’s test. Identify ‘A’ and give its reaction for Iodoform and Tollen’s test.

(b) (i) Give a chemical test to distinguish between ethanal and ethanoic acid.

(ii) Why is the a-hydrogens of aldehydes and ketones are acidic in nature?

(iii) An organic compound ‘A’ with molecular formula C4H8O2 undergoes acid hydrolysis to form two compounds ‘B’ and ‘C. Oxidation of ‘C with acidified potassium permanganate also produces ‘B’. Sodium salt of ‘B’ on heating with soda lime gives methane.

(1) Identify ‘A’, ‘B’ and ‘C.

(2) Out of ‘B’ and ‘C’, which will have higher boiling point? Give reason.

(34) – (a) – (i) Why is boiling point of IM NaCl solution more than that of IM glucose solution?

(ii) A non-volatile solute ‘X’ (molar mass = 50 g mol-¹) when dissolved in 78g of benzene reduced its vapour pressure to 90%. Calculate the mass of X dissolved in the solution.

(iii) Calculate the boiling point elevation for a solution prepared by adding 10g of MgCl, to 200g of water assuming MgCl, is completely dissociated.

(K, for Water = 0.512 K kg mol!, Molar mass MgCl2 = 95g mol-¹)

(b) – (i) Why is the value of Van’t Hoff factor for ethanoic acid in benzene close to 0.5?

(ii) Determine the osmotic pressure of a solution prepared by dissolving 2.32 x 10-2g of K2SO4 in 2L of solution at 25 °C, assuming that K2SO4 is completely dissociated.

(R = 0.082 L atm K-1 mol-1, Molar mass K2SO4 = 174g mol-¹)

(iii) When 25.6g of Sulphur was dissolved in 1000g of benzene, the freezing point lowered by 0.512 K. Calculate the formula of Sulphur (Sx).

(K, for benzene = 5.12 K kg mol-1, Atomic mass of Sulphur = 32g mol-¹)

(35) – (a) A transition element X has electronic configuration [Ar] 4s² 3d³.

Predict its likely oxidation states.

(b) Complete the reaction mentioning all the products formed:

2 KMnO4 → Δ

(c) Account for the following:

(1) In the 3d transition series, zinc has the lowest enthalpy of atomisation.

(ii) Cu ion is unstable in aqueous solution.

(iii) Actinoids show lanthahoids. more number of oxidation states than lanthanoids.

CBSE Class 12 Chemistry Question Paper 2023

Chemistry Question Paper 2023 Class 12

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