CBSE Class 12 Chemistry 2025 — Set 56/5/1

Which of the following aqueous solutions will have the highest freezing point ? (A) 1·0 M KCl (B) 1·0 M Na₂SO₄ (C) 1·0 M Glucose (D) 1·0 M AlCl₃

Which of the following aldehydes will undergo Cannizzaro reaction ? (A) CH₃-CH(CH₃)-CHO (B) (CH₃)₃C-CHO (C) CH₃-CH₂-CHO (D) CH₃-CH(CH₃)-CH(CH₃)-CHO

In which of the following groups are both ions coloured in aqueous solution ? I. Cu⁺ II. Ti⁴⁺ III. Co²⁺ IV. Fe²⁺ [Atomic number : Cu = 29, Ti = 22, Co = 27, Fe = 26] (A) I and II (B) II and III (C) III and IV (D) I and IV

CH₃CH₂CHO and CH₃CH₂COOH can be distinguished by : (A) Sodium bicarbonate test (B) Hinsberg test (C) Iodoform test (D) Lucas test

Match the type of cell given in Column I with their use given in Column II. Column I | Column II i. Lead storage cell | a. Wall clock ii. Mercury cell | b. Apollo Space Programme iii. Dry cell | c. Wrist watch iv. Fuel cell | d. Inverter (A) i-a, ii-b, iii-c, iv-d (B) i-d, ii-c, iii-a, iv-b (C) i-c, ii-d, iii-b, iv-a (D) i-b, ii-a, iii-d, iv-c

While doing qualitative analysis in chemistry lab, Abhishek added yellow coloured potassium chromate solution into a test tube. He was surprised to see the colour of the solution changing immediately to orange. He realised that the test tube was not clean and contained a few drops of some liquid. Which of the following substances will be the most likely liquid to be present in the test tube before adding potassium chromate solution ? (A) Sodium hydrogen carbonate solution (B) Methyl orange solution (C) Sodium hydroxide solution (D) HCl solution

Two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer 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). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A) : For measuring resistance of an ionic solution an AC source is used. Reason (R) : Concentration of ionic solution will change if DC source is used.

Two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer 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). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A) : Henry's law constant (KH) decreases with increase in temperature. Reason (R) : As the temperature increases, solubility of gases in liquids decreases.

Two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer 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). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A) : The solubility of aldehydes and ketones in water decreases with increase in size of the alkyl group. Reason (R) : Aldehydes and ketones have dipole-dipole interaction.

Two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer 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). (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 van der Waals forces of attraction decrease in the order RI > RBr > RCl > RF.

(a) Calculate the elevation of boiling point of a solution when 3 g of CaCl₂ (Molar mass = 111 g mol⁻¹) was dissolved in 260 g of water, assuming that CaCl₂ undergoes complete dissociation. (Kb for water = 0·52 K kg mol⁻¹) OR (b) Liquids 'X' and 'Y' form an ideal solution. The vapour pressure of pure 'X' and pure 'Y' are 120 mm Hg and 160 mm Hg respectively. Calculate the vapour pressure of the solution containing equal moles of 'X' and 'Y'.

| Concentration of KCl solution in mol/L | Conductivity at 298·15 K in S cm⁻¹ | Molar Conductivity at 298·15 K in S cm² mol⁻¹ | | --- | --- | --- | | 1·000 | 0·1113 | 111·3 | | 0·100 | 0·0129 | 129·0 | | 0·010 | 0·00141 | 141·0 | Based on the data given above, give plausible reason for the variation of conductivity and molar conductivity with concentration.

(a) Write the rate law expression for the reaction 2HI arrow H₂ + I₂, if the order of the reaction is zero. (b) What is the effect of temperature on the rate of reaction ? Write a mathematical expression for the same.

Explain the mechanism of acid catalysed hydration of ethene.

(a) How can acetaldehyde be prepared from acetyl chloride ? (b) Propanal is more reactive than propanone towards nucleophilic addition reaction. Give reason.

(a) Shweta mixed two liquids A and B of 10 mL each. After mixing, the volume of the solution was found to be 20·2 mL. (i) Why was there a volume change after mixing the liquids ? (ii) Will there be an increase or decrease of temperature after mixing ? (iii) Give one example for this type of solution. OR (b) (i) How does sprinkling of salt help in clearing the snow covered roads in hilly areas ? (ii) What happens when red blood cells are kept in 0·5% (mass/vol) NaCl solution ? Justify your answer. (iii) Write an application of reverse osmosis.

For the reaction A + B arrow Products, the following initial rates were obtained at various initial concentrations of reactants : | Sl. No. | [A]/mol L⁻¹ | [B]/mol L⁻¹ | Initial rate/mol L⁻¹ s⁻¹ | | --- | --- | --- | --- | | 1 | 0·1 | 0·1 | 0·05 | | 2 | 0·2 | 0·1 | 0·10 | | 3 | 0·1 | 0·2 | 0·05 | Determine the order of the reaction with respect to A and B and overall order of the reaction.

(a) What is meant by crystal field splitting energy ? For a d⁴ ion, write the configuration if (i) Δo < P, and (ii) Δo > P. (b) Explain why in tetrahedral coordination entities, low spin configurations are rarely observed.

Account for the following : (a) The C – Cl bond length in chlorobenzene is shorter than that in methyl chloride. (b) Grignard reagents should be prepared under anhydrous conditions. (c) In case of optically active alkyl halides, SN1 reactions are accompanied by racemisation.

(a) Arrange the following compounds in the increasing order of their acidic strength : 3,5-dinitrophenol, 4-methylphenol, phenol, 2,4,6-trinitrophenol (b) What happens when : (write equations) (i) Phenol is distilled with Zn dust ? (ii) Anisole is treated with HBr ?

An organic compound 'A' (molecular formula C₈H₈O) gives 2,4-DNP test. It does not give Tollen's test, but gives a yellow precipitate 'B' with NaOH and I₂. On drastic oxidation, it gives a carboxylic acid 'C' with formula C₇H₆O₂. Identify 'A', 'B', 'C' and write the reactions involved.

(a) Name the type of linkage responsible for the formation of proteins from α-amino acids. (b) Write any two differences between DNA and RNA.

The following question is a case-based question. Read the case carefully and answer the questions that follow. Carbohydrates are polyhydroxy aldehydes or ketones that represent enormous structural diversity in terms of the arrangement of atoms in space, resulting in hundreds of stereoisomers. Although the chemical properties of most stereoisomers may not be very different, their metabolic rate and utilization in biological systems is significantly different and known to influence the overall carbohydrate metabolism. Structural variants, which arise due to a different arrangement of atoms in three-dimensional space are known as stereoisomers. The number of stereoisomers can be theoretically estimated by using the formula 2ⁿ, where 'n' is the number of stereocenters or asymmetric (chiral) carbon atoms in a molecule. Out of these stereoisomers, there are some structures, which are mirror images of each other, and they are referred to as enantiomers. Answer the following questions : (a) Give chemical reactions to show the presence of an aldehydic group and straight chain in glucose. (b) (i) Define anomers. OR (b) (ii) Draw the structure of β-D-Glucopyranose. (c) Sucrose is known as invert sugar. Explain.

The following question is a case-based question. Read the case carefully and answer the questions that follow. Werner's coordination theory in 1893 was the first attempt to explain the bonding in coordination complexes. It must be remembered that this theory was put forward before the electron had been discovered by J.J. Thomson in 1897, and before the electronic theory of valency. Werner did not have any of the modern instrumental techniques and all his studies were made using simple experimental techniques. Werner was able to explain the nature of bonding in complexes and he concluded that in complexes, the metal shows two different sorts of valency : primary and secondary. Primary valences are normally ionisable whereas secondary valences are non-ionisable. Answer the following questions : (a) One mole of CrCl₃ · 4H₂O precipitates one mole of AgCl when treated with excess of AgNO₃ solution. Write (i) the structural formula of the complex, and (ii) the secondary valency of Cr. (b) What is the difference between a complex and a double salt ? (c) (i) Arrange the following complexes in the increasing order of conductivity of their solution : [Cr(NH₃)₃Cl₃], [Cr(NH₃)₆]Cl₃, [Cr(NH₃)₅Cl]Cl₂ OR (c) (ii) Write two differences between primary and secondary valences in coordination compounds.

(a) (i) For a galvanic cell, the following half reactions are given. Decide, which will remain as reduction reaction and which will be reversed to become an oxidation reaction. Give reason for your answer. (I) Cr³⁺ + 3e⁻ arrow Cr(s); E° = -0·74 V (II) Fe²⁺ + 2e⁻ arrow Fe(s); E° = -0·44 V (ii) Represent the cell in which the following reaction takes place : Mg(s) + 2Ag⁺ (0·001M) arrow Mg²⁺ (0·100M) + 2Ag(s) Calculate Ecell if E°cell = 3·17 V. (log 10 = 1) OR (b) (i) State Kohlrausch's law. Give any two applications of it. (ii) Lambda°mNH₄Cl, Lambda°mNaOH and Lambda°mNaCl are 129·8, 217·4 and 108·9 S cm² mol⁻¹ respectively. Molar conductivity of 1 × 10⁻² M solution of NH₄OH is 9·33 S cm² mol⁻¹. Calculate the degree of dissociation (α) of NH₄OH solution at this concentration.

(a) (i) In a chemistry practical class, the teacher gave his students an amine 'X' having molecular formula C₂H₇N, and asked the students to identify the type of amine. One of the students, Neeta, observed that it reacts with C₆H₅SO₂Cl, to give a compound which dissolves in NaOH solution. Can you help Neeta to identify the compound 'X' ? (ii) Arrange the following in the increasing order of their pKb value in aqueous phase : C₆H₅NH₂, (CH₃)₂NH, NH₃, CH₃NH₂, (CH₃)₃N (iii) Aniline on nitration gives considerable amount of meta product along with ortho and para products. Why ? (iv) Convert aniline to : (I) p-bromoaniline (II) phenol OR (b) (i) Arun heated a mixture of ethylamine and CHCl₃ with ethanolic KOH, which forms a foul smelling gas. Write the chemical equation involved. (ii) Identify A and B in the following reactions : A xrightarrow[ethanol]H₂/Pd Aniline (C₆H₅NH₂, drawn ring bearing -NH₂) xleftarrowBr₂/NaOH B (both arrows point TOWARDS aniline: A is converted to aniline by H₂/Pd in ethanol; B is converted to aniline by Br₂/NaOH) (iii) Convert aniline to : (I) benzene (II) sulphanilic acid

(a) (i) When pyrolusite ore is fused with KOH, in presence of air, a dark green coloured product 'A' is obtained which changes to purple coloured compound 'B' in acidic medium. (I) Write the formulae of 'A' and 'B'. (II) Write the ionic equation for the reaction when compound 'B' reacts with Fe²⁺ in acidic medium. (ii) Give reasons : (I) Ce⁴⁺ in aqueous solution is a good oxidising agent. (II) The actinoid contraction is greater from element to element than lanthanoid contraction. (III) E°Zn²⁺/Zn value is more negative than expected, whereas E°Cu²⁺/Cu is positive. OR (b) (i) While studying the periodic properties, Arti came across an abnormal behaviour in the atomic size of Hf. She found that, even though Hf is placed below Zr in the same group, both have almost similar atomic sizes. (I) Which phenomenon is responsible for the above behaviour ? Define it. (II) Mention any other consequence of the above phenomenon. (ii) Give reasons for the following : (I) Transition metals exhibit catalytic properties. (II) Transition metals have high enthalpy of atomisation. (III) Sc is a transition element, while Zn is not.