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) \(\rightarrow\) 2Cu (s) + Zn2+ (aq)

Eocell = 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 Ti3+, Cr3+, Fe2+ and Ni2+ ions, the one which is the most stable ion in aqueous solution is:

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

Hofmann Bromamide degradation reaction is given by:

• (A) R – NO2
• (B) R – NH2
• (C) R – CH2 – NH2
• (D) R – CO – NH2

The value of Henry’s constant KH 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 correct statement is:

• (A) La is actually not an element of transition series.
• (B) Zr and Hf have almost identical atomic radii.
• (C) Lanthanoids are radioactive.
• (D) Ionic radius increases from La\textsuperscript{3+} to Lu\textsuperscript{3+}.

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

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 FeO to Fe\textsubscript{2}O\textsubscript{3}?

• (A) 1F
• (B) 2F
• (C) 3F
• (D) 4F

Alkenes are formed by heating alcohols with conc. H\textsubscript{2}SO\textsubscript{4}. 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.

Assertion (A): Cuprous salts are diamagnetic.

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

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.

Assertion (A): Electrolysis of aqueous NaCl gives H\textsubscript{2 at cathode and Cl\textsubscript{2 at anode.

Reason (R): Chlorine has higher oxidation potential than H\textsubscript{2O.

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

Identify and draw the main products formed in the following chemical reactions:

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 A\textsubscript{2} (g) and B\textsubscript{2} (g) was carried out in a sealed isothermal container. The rate law for the reaction was found to be:

Rate = k[A\textsubscript{2}][B\textsubscript{2}]

If 1 mole of A\textsubscript{2} (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:
0 & 0.88
1 & 0.44
2 & 0.22
3 & 0.11
Based on the above data, predict the order of the reaction and write the expression for the rate law.

Give explanation for each of the following observations:

(a) With the same d-orbital configuration (d\textsuperscript{4), Mn\textsuperscript{3+ ion is an oxidising agent whereas Cr\textsuperscript{2+ 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 C\textsubscript{8}H\textsubscript{8}O 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 KMnO\textsubscript{4} 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\textsubscript{b values

C\textsubscript{2H\textsubscript{5NH\textsubscript{2, (C\textsubscript{2H\textsubscript{5)\textsubscript{2NH, C\textsubscript{6H\textsubscript{5NHCH\textsubscript{3, C\textsubscript{6H\textsubscript{5NH\textsubscript{2

(b) In increasing order of boiling point

C\textsubscript{2H\textsubscript{5OH, C\textsubscript{2H\textsubscript{5NH\textsubscript{2, (CH\textsubscript{3)\textsubscript{2NH

(c) In increasing order of solubility in water

C\textsubscript{6H\textsubscript{5NH\textsubscript{2, (C\textsubscript{2H\textsubscript{5)\textsubscript{2NH, C\textsubscript{2H\textsubscript{5NH\textsubscript{2

(a) 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 alcoholic AgCN.

(iii) Methyl chloride reacts faster with OH\textsuperscript{-- ion in S\textsubscript{N2 reaction than t-butyl chloride.

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

(i) CH\textsubscript{3CH=CH\textsubscript{2 \xrightarrow[\text{Peroxide]{\text{HBr ‘A’ \xrightarrow{\text{aq. KOH ‘B’

(ii) \chemfig{CH_3CH_2C(CH_3)(Cl) \xrightarrow{\text{alc. KOH, \Delta ‘A’ \xrightarrow{\text{HBr ‘B’

(iii) ‘A’ \xrightarrow{\text{Mg CH\textsubscript{3CH\textsubscript{2MgCl \xrightarrow[\text{H\textsuperscript{+]{H\textsubscript{2O ‘B’ (Main product)

(a) Can sodium propoxide and t-butyl chloride be used for the preparation of t-butyl propyl ether? Give suitable explanation.

(b) Give the IUPAC name of the above mentioned 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\textsuperscript{-1. Calculate the percentage dissociation of NaOH in this solution.

[Atomic mass: Na = 23, O = 16, H = 1]

Calculate the cell voltage of the voltaic cell which is set up by joining the following half-cells at 25\(^\circ\)C:

Al/Al\textsuperscript{3+ (0.002 M) and Ni/Ni\textsuperscript{2+ (0.002 M)

Given: \(E^\circ_{Ni^{2+}/Ni} = -0.25\) V
\(E^\circ_{Al^{3+}/Al} = -1.66\) V
\(\log 5 = 0.6990\)

Give one example of miscible liquid pair which shows negative deviation from Raoult’s law. What is the reason for such deviation?

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.

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.

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

[Ni(CO)\(_4\)] is diamagnetic whereas [NiCl\(_4\)]\(^{2-}\) is paramagnetic. [Atomic number: Ni = 28]

CO is a stronger complexing agent than NH\(_3\).

The trans isomer of complex [Co(en)\(_2\)Cl\(_2\)]\(^+\) is optically inactive.

Using Crystal Field theory, write the number of unpaired electrons in octahedral complexes of Fe\(^{3+}\) 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) [Co(NH\(_3\))\(_6\)][Cr(CN)\(_6\)]

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

(III) [Co(NH\(_3\))\(_3\)(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:

N\(_2\)O\(_5\) (g) → 2NO\(_2\) (g) + \(\frac{1{2}\) O\(_2\) (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]

We cannot determine the order of a reaction by taking into consideration the balanced chemical equation.

A bimolecular reaction may become kinetically of 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 JK\(^{-1}\) 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.

(a)(i) Complete the following reactions by writing the structure of the main products:

(a) (ii) Give simple chemical test to distinguish between the following pairs of compounds:

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

(b) (ii) Carry out the following conversions: