CBSE Class 12 2025 Chemistry 56-4-3 Question Paper Set-3: Download Solutions with Answer Key

In an electrochemical cell, the following reaction takes place:

2Cu⁺(aq) + Zn(s) → 2Cu(s) + Zn²⁺(aq)

E°_cell = 1.28 V

As the reaction progresses, what will happen to the overall voltage of the cell?

• (A) Voltage will remain constant.
• (B) It will decrease as [Zn²⁺] increases.
• (C) It will increase as [Cu⁺] increases.
• (D) It will increase as [Zn²⁺] increases.

Out of \( \mathrm{Ti^{3+}} \), \( \mathrm{Cr^{3+}} \), \( \mathrm{Fe^{2+}} \) and \( \mathrm{Ni^{2+}} \) ions, the one which is the most stable ion in aqueous solution is:

[Atomic number : Ti = 22, Cr = 24, Fe = 26, Ni = 28]

• (A) Ti³⁺
• (B) Cr³⁺
• (C) Fe²⁺
• (D) Ni²⁺

Hoffmann Bromamide degradation reaction is given by:

• (A) ArNO\(_2\)
• (B) ArNH\(_2\)
• (C) ArCONH\(_2\)
• (D) ArCH\(_2\)NH\(_2\)

The value of Henry's constant K_H is:

• (A) greater for gases with higher solubility
• (B) greater for gases with lower solubility
• (C) constant for all gases
• (D) not related to the solubility of gases

In the Haworth structure of the following carbohydrate, various carbon atoms have been numbered. The anomeric carbon is numbered as:

• (A) 1
• (B) 2
• (C) 3
• (D) 5

Out of the following statements, the incorrect statement is:

• (A) La is actually an element of transition series.
• (B) Zr and Hf have almost identical atomic radii because of lanthanoid contraction.
• (C) Ionic radius decreases from La\(^{3+}\) to Lu\(^{3+}\) ion.
• (D) Lanthanoids are radioactive in nature.

In the given reaction sequence, the structure of Y would be:

Aniline ⟶[NaNO₂/HCl, 0-5°C] X ⟶[C₂H₅OH] Y

• (A) Phenol
• (B) Benzene
• (C) Diazo coupling product
• (D) Chlorobenzene

Out of 2-Bromobutane, 1-Bromobutane, 2-Bromopropane and 1-Bromopropane, the molecule which is chiral in nature is:

• (A) 2-Bromobutane
• (B) 1-Bromobutane
• (C) 2-Bromopropane
• (D) 1-Bromopropane

Which of the following properties of transition metals enables them to behave as catalysts?

• (A) High melting point
• (B) High ionisation enthalpy
• (C) Alloy formation
• (D) Variable oxidation states

What amount of electric charge is required for the oxidation of 1 mole of \( \mathrm{FeO} \) to \( \mathrm{Fe_2O_3} \)?

• (A) 1F
• (B) 2F
• (C) 3F
• (D) 4F

Alkenes are formed by heating alcohols with conc. H₂SO₄. The first step in the reaction is:

• (A) formation of carbocation
• (B) formation of ester
• (C) protonation of alcohol molecule
• (D) elimination of water

Polyhalogen compounds have wide application in industries and agriculture. DDT is also a very important polyhalogen compound. It is a:

• (A) greenhouse gas
• (B) fertilizer
• (C) biodegradable insecticide
• (D) non-biodegradable insecticide

Assertion (A): Acetanilide is less basic than aniline.

Reason (R): Acetylation of aniline results in decrease of electron density on nitrogen.

• (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): Cuprous salts are diamagnetic.

Reason (R): Cuprous ion has completely filled 3d-orbitals.

• (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): n-Butyl chloride has higher boiling point than n-Butyl bromide.

Reason (R): C–Cl bond is more polar than C–Br bond.

• (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): Electrolysis of aqueous NaCl gives H₂ at cathode and Cl₂ at anode.

Reason (R): Chlorine has higher oxidation potential than H₂O.

• (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.

What is meant by essential amino acids? Why are amino acids amphoteric in nature?

Write the structures of the main products of the following reactions:

(a) methyl 3-(2-oxocyclohexyl)propanoate ⟶[NaBH₄]

(b) 6 CH₃–C(CH₃)₂–OH + 2 Al →

Name and define the cell which was used for providing electric power in the Apollo space programme. Also write its one advantage.

PdCl₂·2KCl does not give precipitate of AgCl with AgNO₃ solution. Write the structural formula and IUPAC name of the complex.

The reaction between A₂(g) and B₂(g) was carried out in a sealed isothermal container. The rate law for the reaction was found to be:

Rate = k[A₂][B₂]

If 1 mole of A₂(g) was added to the reaction chamber and the temperature was kept constant, then predict the change in rate of the reaction and the rate constant.

Reactant 'A' underwent a decomposition reaction. The concentration of 'A' was measured periodically and recorded in the table given below:

Give explanation for each of the following observations:

(a) With the same d-orbital configuration (d⁴), Mn³⁺ ion is an oxidising agent whereas Cr²⁺ ion is a reducing agent.

(b) Actinoid contraction is greater from element to element than that among lanthanoids.

(c) Transition metals form large number of interstitial compounds with H, B, C and N.

An aromatic compound 'A' with molecular formula C₈H₈O gives positive 2,4-DNP test. It gives yellow precipitate of compound 'B' on treatment with sodium hypoiodite. Compound 'A' does not react with Tollen's or Fehling's reagent; on drastic oxidation with KMnO₄ it forms a carboxylic acid 'C'. Elucidate the structures of A, B and C. Also give their IUPAC names.

Arrange the following compounds as asked:

(a) in decreasing order of pK_b values

C₂H₅NH₂, (C₂H₅)₂NH, C₆H₅NHCH₃, C₆H₅NH₂

(b) increasing order of boiling point

C₂H₅OH, C₂H₅NH₂, (CH₃)₂NH

(c) increasing order of solubility in water

C₆H₅NH₂, (C₂H₅)₂NH, C₂H₅NH₂

Account for the following:

(i) Allyl chloride is hydrolysed more readily than n-propyl chloride.

(ii) Isocyanides are formed when alkyl halides are treated with silver cyanide.

(iii) Methyl chloride reacts faster with OH⁻ ion in S_N2 reaction than t-butyl chloride.

Complete the following reactions by writing the structural formulae of 'A' and 'B':

(i) \( \mathrm{CH_3CH=CH_2} \xrightarrow[\text{Peroxide}]{\text{HBr}} \) 'A' \( \xrightarrow{\text{aq. KOH}} \) 'B'

(ii) \( \mathrm{CH_3CH_2CH(Cl)CH_3} \xrightarrow[\Delta]{\text{alc. KOH}} \) 'A' \( \xrightarrow{\text{HBr}} \) 'B'

(iii) 'A' \( \xrightarrow{\text{Mg}} \mathrm{CH_3CH_2MgCl} \xrightarrow[\mathrm{H^+}]{\mathrm{H_2O}} \) 'B' (Main product)

Can sodium propoxide and t-butyl chloride be used for the preparation of t-butyl propyl ether? Give suitable explanation. Justify your answer by suggesting the appropriate starting material required for the preparation of t-butyl propyl ether.

Give the IUPAC name of the above mentioned ether (t-butyl propyl ether).

An aqueous solution of NaOH was made and its molar mass from the measurement of osmotic pressure at 25\(^{\circ}\)C was found to be 28 g mol\(^{-1}\). Calculate the percentage dissociation of NaOH in this solution.
[Atomic mass: Na = 23.0 u, O = 16.0 u, H = 1.0 u]

Calculate the cell voltage of the voltaic cell which is set up by joining the following half-cells at 25°C:

Al/Al³⁺ (0.002 M) and Ni/Ni²⁺ (0.002 M)

Given: E°_Ni²⁺/Ni = −0.25 V, E°_Al³⁺/Al = −1.66 V, log 5 = 0.6990

According to the generally accepted definition of the ideal solution there are equal interaction forces acting between molecules belonging to the same or different species. (This is equivalent to the statement that the activity of the components equals the concentration.) Strictly speaking, this condition is fulfilled only in exceptional cases for mixtures (optical isomers, isotopic mixtures of an element, hydrocarbon mixtures). It is still usual to talk about ideal solutions as limiting cases in reality since very dilute solutions behave ideally with respect to the solvent. This view is further supported by the fact that Raoult's law empirically found for describing the behaviour of the solvent in dilute solutions can be deduced thermodynamically via the assumption of ideal behaviour of the solvent.

State Raoult's law for a solution containing volatile components.

Raoult's law is a special case of Henry's law. Comment.

Write two characteristics of an ideal solution.

Ribose and 2-deoxyribose have an important role in biology. Among the most important derivatives are those with phosphate groups attached at the 5 position. Mono-, di- and tri-phosphate forms are important, as well as 3-5 cyclic monophosphates. Purines and pyrimidines form an important class of compounds with ribose and deoxyribose. When these purine and pyrimidine derivatives are coupled to a ribose sugar, they are called nucleosides.

Answer the following questions:

What products would be formed when DNA is hydrolysed? How is DNA different from RNA with reference to a structure?

Differentiate between nucleotide and nucleoside.

Mention two important functions of nucleic acid.

(c) (ii) Name the linkage which joins two nucleotides. Name the base that is found in nucleotide of RNA but not in DNA.

Give reasons:
(I) \([ \text{Ni(CO)}_4 ]\) is diamagnetic whereas \([ \text{NiCl}_4 ]^{2-}\) is paramagnetic. [Atomic number: Ni = 28]
(II) CO is a stronger complexing agent than NH\(_3\).
(III) The trans isomer of complex \([ \text{Co(en)}_2\text{Cl}_2 ]^{+}\) is optically inactive.

Give reasons:

CO is a stronger complexing agent than NH₃.

Give reasons:

The trans isomer of complex [Co(en)₂Cl₂]⁺ is optically inactive.

Using Crystal Field theory, write the number of unpaired electrons in octahedral complexes of Fe²⁺ in the presence of:

(I) Strong field ligand

(II) Weak field ligand

[Atomic number: Fe = 26]

Name the type of isomerism exhibited by the following compounds. Also, draw their corresponding isomers.

(I) \( [\text{Co(NH}_3\text{)}_6][\text{Cr(CN)}_6] \)

(II) \( [\text{Co(en)}_3]^{3+} \)

(III) \( [\text{Co(NH}_3\text{)}_3(\text{NO}_2)_3] \)

Name the type of isomerism exhibited by the following compounds. Also, draw their corresponding isomers.

(I) \( [\text{Co(NH}_3\text{)}_6][\text{Cr(CN)}_6] \)

(II) \( [\text{Co(en)}_3]^{3+} \)

(III) \( [\text{Co(NH}_3\text{)}_3(\text{NO}_2)_3] \)

Name the type of isomerism exhibited by the following compounds. Also, draw their corresponding isomers.

(I) \( [\text{Co(NH}_3\text{)}_6][\text{Cr(CN)}_6] \)

(II) \( [\text{Co(en)}_3]^{3+} \)

(III) \( [\text{Co(NH}_3\text{)}_3(\text{NO}_2)_3] \)

Differentiate between weak field and strong field ligands. How does the strength of the ligand influence the spin of the complex?

The initial concentration of N\(_2\)O\(_5\) in the first-order reaction:
\[ \text{N}_2\text{O}_5 (\text{g}) \rightarrow 2 \text{NO}_2 (\text{g}) + \frac{1}{2} \text{O}_2 (\text{g}) \] was \( 1.2 \times 10^{-2} \) mol L\(^{-1}\). The concentration of N\(_2\)O\(_5\) after 60 minutes was \( 0.2 \times 10^{-2} \) mol L\(^{-1}\). Calculate the rate constant of the reaction at 318 K.
\([ \log 6 = 0.778 ]\)

Account for the following:
(I) We cannot determine the order of a reaction by taking into consideration the balanced chemical equation.
(II) A bimolecular reaction may become kinetically first order under a specified condition.

Account for the following:
(I) We cannot determine the order of a reaction by taking into consideration the balanced chemical equation.
(II) A bimolecular reaction may become kinetically first order under a specified condition.

The rate of the chemical reaction doubles for an increase of 10 K in absolute temperature from 298 K. Calculate activation energy (E_a).

[2.303 R = 19.15 J K⁻¹ mol⁻¹, log 2 = 0.3]

For the reaction:
2H\(_2\)O\(_2\) \(\xrightarrow{I^-}\) 2H\(_2\)O + O\(_2\)
Given mechanism:
(I) H\(_2\)O\(_2\) + I\(^-\) → H\(_2\)O + IO\(^-\) (slow)
(II) H\(_2\)O\(_2\) + IO\(^-\) → H\(_2\)O + I\(^-\) + O\(_2\) (fast)
(1) Write rate law for the reaction.
(2) Write the overall order and molecularity of the reaction.

Complete the following reactions by writing the structure of the main products:

Cyclohexanone + H₂NCONH–NH₂ →

Complete the following reactions by writing the structure of the main products:

(CH₃)₂Cd + 2 CH₃COCl →

Complete the following reactions by writing the structure of the main products:

Benzoyl chloride ⟶[H₂, Pd–BaSO₄]

Give a simple chemical test to distinguish between benzoic acid and ethyl benzoate.

Give a simple chemical test to distinguish between propanal and propanone.

(i) Complete each synthesis by giving missing starting material, reagent or products:

(I) p-cresol ⟶[(i) KMnO₄, KOH; (ii) H₃O⁺] ?

(II) ? ⟶? p-methylbenzaldehyde (or analogous synthesis)

(III) ? ⟶[[Ag(NH₃)₂]⁺] benzoic acid (from benzaldehyde)

(ii) Carry out the following conversions:

(I) Benzaldehyde to Benzophenone

(II) Benzaldehyde to 3-phenyl propanol