CBSE Class 12 Chemistry Question Paper 2025 with Solutions Set 3 – 56/1/3 ( Available)- Download PDF

Standard electrode potential for Sn⁴⁺/Sn²⁺ couple is +0.15 V and that for the Cr³⁺/Cr couple is -0.74 V. The two couples in their standard states are connected to make a cell. The cell potential will be

• (A) +1.19 V
• (B) +0.89 V
• (C) +0.18 V
• (D) +1.83 V

The magnetic moment is associated with its spin angular momentum and orbital angular momentum. Spin only magnetic moment value of Cr³⁺ ion (Atomic no. : Cr = 24) is

• (A) 2.87 B.M.
• (B) 3.87 B.M.
• (C) 3.47 B.M.
• (D) 3.57 B.M.

In case of association, abnormal molar mass of solute will: 

• (A) increase
  
• (B) decrease
  
• (C) remain same
  
• (D) first increase and then decrease

Alkyl halides undergoing nucleophilic bimolecular substitution reaction involve

• (A) retention of configuration
• (B) formation of racemic mixture
• (C) inversion of configuration
• (D) formation of carbocation

Arrange the following compounds in increasing order of their boiling points:
 

• (A) (ii) < (i) < (iii)
  
• (B) (iii) < (i) < (ii)
  
• (C) (i) < (ii) < (iii)
  
• (D) (iii) < (ii) < (i)
  

The correct IUPAC name of [Pt(NH₃)₂Cl₂]²⁺ is

• (A) Diamminedichloridoplatinum(II)
• (B) Diamminedichloridoplatinum(IV)
• (C) Diamminedichloridoplatinum(O)
• (D) Diamminedichloridoplatinate(IV)

The acid formed when propyl magnesium bromide is treated with CO₂ followed by acid hydrolysis is :

• (A) C₃H₇COOH
• (B) C₂H₅COOH
• (C) CH₃COOH
• (D) C₃H₇OH

Acidified \(KMnO_4\) oxidizes sulphite to: 

• (A) \(S_2O_3^{2-} \)
• (B) \(S_2O_8^{2-} \)
• (C) \(SO_2(g) \)
• (D) \(SO_4^{2-} \)

Which is the correct order of acid strength from the following ?

• (A) C₆H₅OH > H₂O > ROH
• (B) C₆H₅OH > ROH > H₂O
• (C) ROH > C₆H₅OH > H₂O
• (D) H₂O > C₆H₅OH > ROH

An unripe mango placed in a concentrated salt solution to prepare pickle, shrivels because

• (A) it gains water due to osmosis
• (B) it loses water due to reverse osmosis
• (C) it gains water due to reverse osmosis
• (D) it loses water due to osmosis

The best reagent for converting propanamide into propanamine is

• (A) excess H₂
• (B) Br₂ in aqueous NaOH
• (C) iodine in the presence of red phosphorus
• (D) LiAlH₄ in ether

Which of the following statements is not true about glucose ?

• (A) It is an aldohexose.
• (B) On heating with HI it forms n-hexane.
• (C) It exists in furanose form.
• (D) It does not give Schiff's test.

Assertion (A): All naturally occurring \(\alpha\)-amino acids except glycine are optically active. Reason (R): Most naturally occurring amino acids have L-configuration.

• (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).
  
• (C) Assertion (A) is true, but Reason (R) is false.
  
• (D) Assertion (A) is false, but Reason (R) is true. 
   

Assertion (A): The boiling point of ethanol is higher than that of methoxymethane. 
Reason (R): There is intramolecular hydrogen bonding in ethanol. 

• (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).
  
• (C) Assertion (A) is true, but Reason (R) is false.
  
• (D) Assertion (A) is false, but Reason (R) is true. 
   

Assertion (A): The boiling points of alkyl halides decrease in the order: RI>RBr>RCl>RF. 
Reason (R): The boiling points of alkyl chlorides, bromides and iodides are considerably higher than that of the hydrocarbon of comparable molecular mass.

• (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).
  
• (C) Assertion (A) is true, but Reason (R) is false.
  
• (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A): [Cr(H_2O)_6]Cl_2 and [Fe(H_2O)_6]Cl_2 are examples of homoleptic complexes. 
Reason (R): All the ligands attached to the metal are the same.

• (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).
  
• (C) Assertion (A) is true, but Reason (R) is false.
  
• (D) Assertion (A) is false, but Reason (R) is true. 
   

Would you expect benzaldehyde to be more reactive or less reactive in nucleophilic addition reactions than propanal ? Justify your answer.

Complete and balance the following chemical equations :
(a) \(\mathrm{8MnO_4^- + 3S_2O_3^{2-} + H_2O \longrightarrow}\)
(b) \(\mathrm{Cr_2O_7^{2-} + 3Sn^{2+} + 14H^+ \longrightarrow}\)

Give reasons : (1+1=2)

(a) Cooking is faster in pressure cooker than in an open pan.

(b) On mixing liquid X and liquid Y, volume of the resulting solution decreases. What type of deviation from Raoult's law is shown by the resulting solution ? What change in temperature would you observe after mixing liquids X and Y ?

Define Azeotrope. What type of Azeotrope is formed by negative deviation from Raoult's law ? Give an example.

Identify A and B in each of the following reaction sequence:

(a) \[ \mathrm{CH_3CH_2Cl} \xrightarrow{\mathrm{NaCN}} \mathrm{A} \xrightarrow{\mathrm{H_2/Ni}} \mathrm{B} \]

(b) \[ \mathrm{C_6H_5NH_2} \xrightarrow[0-5^\circ \mathrm{C}]{\mathrm{NaNO_2/HCl}} \mathrm{A} \xrightarrow[\mathrm{H^+}]{\mathrm{C_6H_5NH_2}} \mathrm{B} \]

What are the hydrolysis products of (i)sucrose and (ii)lactose ?

Henry's law constant for \(\mathrm{CO_2}\) in water is \(1.67 \times 10^{8}\) Pa at 298 K. Calculate the number of moles of \(\mathrm{CO_2}\) in 500 ml of soda water when packed under \(2.53 \times 10^{5}\) Pa at the same temperature.

Calculate \(\Delta_r G^{\circ}\) and \(\log K_C\) of the reaction.

\(\mathrm{2Cr(s) + 3Cd^{2+}(aq) \to 2Cr^{3+}(aq) + 3Cd(s)}\)

Given \(E^{\circ}_{\mathrm{Cr^{3+}/Cr}} = -0.74\) V, \(E^{\circ}_{\mathrm{Cd^{2+}/Cd}} = -0.40\) V

[R = 8.314 J \(\mathrm{K^{-1}\,mol^{-1}}\), F = 96500 C \(\mathrm{mol^{-1}}\)]

The rate of a reaction quadruples when the temperature changes from 293 K to 313 K. Calculate the energy of activation of the reaction assuming that it does not change with temperature.
[Given : \(\log 4 = 0.602,\ \log 2 = 0.301,\ R = 8.314\ \mathrm{J\ K^{-1}\ mol^{-1}}\)]

Draw the structure of the major monohalo product for each of the following reactions : (1+1+1=3)

(a)

(b)

(c)

How do you convert :

Chlorobenzene to biphenyl

How do you convert :

Propene to 1-Iodopropane

How do you convert :

2-bromobutane to but-2-ene.

The elements of the 3d transition series are given as: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn. Answer the following:

Copper has an exceptionally positive \( E^\circ_{\text{M}^{2+}/\text{M}} \) value, why?

Arrange the following compounds in increasing order of their boiling point :

(CH₃)₂NH, CH₃CH₂NH₂, CH₃CH₂OH.

Give plausible explanation for each of the following :

(i) Aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis.

(ii) Amides are less basic than amines.

Define the following terms :
(a) Native protein
(b) Nucleotide
(c) Essential amino acid

Read the passage carefully and answer the questions that follow.
Passage: The rate of a chemical reaction is expressed either in terms of decrease in the concentration of reactants or increase in the concentration of a product per unit time. Rate of the reaction depends upon the nature of reactants, concentration of reactants, temperature, presence of catalyst, surface area of the reactants and presence of light. Rate of reaction is directly related to the concentration of reactant. Rate law states that the rate of reaction depends upon the concentration terms on which the rate of reaction actually depends, as observed experimentally. The sum of powers of the concentration of the reactants in the Rate law expression is called order of reaction while the number of reacting species taking part in an elementary reaction which must collide simultaneously in order to bring about a chemical reaction is called molecularity of the reaction.
 Answer the following questions:

What is the effect of temperature on the rate constant of a reaction ? (1)

Why is molecularity applicable only for elementary reactions whereas order is applicable for elementary as well as complex reactions ? (1)

The conversion of molecule X to Y follows second order kinetics. If concentration of X is increased 3 times, how will it affect the rate of formation of Y ? (1)

Phenols undergo electrophilic substitution reactions readily due to the strong activating effect of OH group attached to the benzene ring. Since, the OH group increases the electron density more to o- and p- positions therefore OH group is ortho, para-directing. Reimer-Tiemann reaction is one of the examples of aldehyde group being introduced on the aromatic ring of phenol, ortho to the hydroxyl group. This is a general method used for the ortho-formylation of phenols.
Answer the following questions:

Why phenol does not undergo protonation readily ? (1)

Which is a stronger acid - phenol or cresol ? Give reason. (1)

(c) Write the IUPAC name of the product formed in the Reimer-Tiemann reaction. (1)

(a) Carry out the following conversions : (2+3=5)

(i) Ethanal to But-2-enal

(ii) Propanoic acid to ethane

(b) An alkene A with molecular formula C₅H₁₀ on ozonolysis gives a mixture of two compounds B and C. Compound B gives positive Fehling test and also reacts with iodine and NaOH solution. Compound C does not give Fehling solution test but forms iodoform. Identify the compounds A, B and C.

An organic compound (A) (molecular formula C₈H₁₆O₂) was hydrolysed with dilute sulphuric acid to get a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (C) on dehydration gives But-1-ene. Identify (A), (B) and (C) and write chemical equations for the reactions involved.

In the following complex ion, explain the type of hybridisation, shape and magnetic property :

\(\mathrm{[Fe(H_2O)_6]^{2+}}\)

(At. Nos. : Fe = 26, Ni = 28)

In the following complex ion, explain the type of hybridisation, shape and magnetic property :

\(\mathrm{[Fe(H_2O)_6]^{2+}}\)

(At. Nos. : Fe = 26, Ni = 28)

Write IUPAC names of the following :

(i) \( [\mathrm{Co(H_2O)(CN)(en)_2}]^{2+} \)

(ii) \( [\mathrm{PtCl_4}]^{2-} \)

(iii) \( [\mathrm{Cr(NH_3)_4Cl(ONO)}]^{+} \)

What is spectrochemical series ? Write the difference between a strong field ligand and a weak field ligand.

Write the cell reaction and calculate the e.m.f. of the following cell at 298 K:
\[ \text{Sn}(s) \mid \text{Sn}^{2+} (\text{0.004 M}) \parallel \text{H}^+ (\text{0.02 M}) \mid \text{H}_2 (\text{1 Bar}) \mid \text{Pt}(s) \]
(Given: \( E^\circ_{\text{Sn}^{2+}/\text{Sn}} = -0.14 \, \text{V}, E^\circ_{\text{H}^+/\text{H}_2} = 0.00 \, \text{V} \))

Account for the following :

(i) On the basis of E° values, O₂ gas should be liberated at anode but it is Cl₂ gas which is liberated in the electrolysis of aqueous NaCl.

(ii) Conductivity of CH₃COOH decreases on dilution.

Write the anode and cathode reactions and the overall cell reaction occurring in a lead storage battery during its use.

Calculate the potential for half-cell containing 0.01 M K₂Cr₂O₇(aq), 0.01 M Cr³⁺(aq) and 1.0 × 10^-4 M H⁺(aq).

The half cell reaction is

Cr₂O₇^2-(aq) + 14H⁺(aq) + 6e^- → 2Cr³⁺(aq) + 7H₂O(l)

and the standard electrode potential is given as E° = 1.33 V.

[Given : log 10 = 1]