CBSE 12 Chemistry 20 Most Expected Questions 2025 For Exam Day

1

Given that blood cells maintain their shape in a 0.9% sodium chloride solution, explain what happens to them when they are immersed in: (a) a higher concentration (1.2%) sodium chloride solution, and (b) a lower concentration (0.4%) sodium chloride solution.

2

At 25°C, pure liquids X and Y have vapor pressures of 120 mmHg and 160 mmHg, respectively. Assuming an ideal solution forms when equal moles of X and Y are mixed, determine the solution's vapor pressure.

3

Explain what is lanthanoid contraction, and what are the consequences of lanthanold contraction?

4

Give reasons for the following features of transition metal chemistry:

(i) The transition metals and their compounds are usually paramagnetic.

(ii) The transition metals exhibit variable oxidation states.

5

Suggest reasons for the following:

(i) Osmotic pressure measurement is particularly well-suited for determining the molar masses of large molecules like proteins and polymers.

(ii) Elevation of boiling point of 1 M KCI solution is nearly double that of 1. M sugar solution.

6

Given the lead storage cell, mercury cell, fuel cell, and dry cell, identify: (i) the cell used in hearing aids, (ii) the cell used in the Apollo Space Programme, (iii) the cell used in automobiles and inverters, and (iv) the cell with the shortest lifespan.

7

Calculate the mass of NaCI (molar mass = 58.5 g mol ^-1) to be dissolved in 37.2g of water to lower the freezing point by 2° C, assuming that NaCl undergoes complete dissociation. (K, for water = 1.86 K kg mol ^-1).

8

For the reaction Cu(s) + 2Ag⁺(aq) → Cu²⁺(aq) + 2Ag(s), (i) construct the galvanic cell representation and (ii) identify the half-reactions occurring at the cathode and anode

9

Name the cell which is generally used in hearing aids. Write the reactions taking place at the anode and the cathode of this cell.

10

Using Williamson's ether synthesis, identify the necessary alkyl bromide and sodium alkoxide reactants to produce 2-ethoxy-3-methylpentane.

11

For a second-order reaction with respect to a reactant, (a) determine the effect on the reaction rate when the reactant concentration is decreased to 50%. (b) State the units of the rate constant.

12

Write the equations involved in the following reactions:

(i) Stephen reaction.

(ii) Wolff-Kishner reaction.

(iii) Etard reaction.

13

Explain the effect of adding a catalyst on:

(i) Activation energy (Ea) and

(ii) Gibbs energy (AG) of a reaction?

14

Explain Azeotrope. What type of azeotrope is formed by negative deviation from Raoult's law? Explain with examples.

15

Demonstrate that the time for 99% reaction completion is double the time for 90% completion.

16

State one similarity and one difference between lanthanide and actinide chemistry.

17

Write IUPAC name of the complex [Pt(en),Cl,]. Draw structures of geometrical isomers for this complex.

18

A coordination compound, CrCl₃·5H₂O, reacts with AgNO₃ to produce 2 moles of AgCl precipitate per mole of the compound. Determine the structural formula of the complex.

19

Describe the steps and reagents required for the following conversions: 

(i) aniline to bromobenzene, 

(ii) chlorobenzene to 2-chloroacetophenone, and (iii) chloroethane to butane.

20

How would you obtain: 

(i) picric acid from phenol?

(ii) -methyl propanol from 2-methyl propene?