List of top Questions asked in CBSE CLASS XII

For the reaction:
2 AgCl(s) + H₂(g) (0.4 atm) → 2 Ag(s) + 2 H⁺(0.1 M) + 2 Cl^-(0.2 M)
Calculate the emf of the cell at 25 °C.
Given: ΔG° = -43500 J mol^-1. [log 10 = 1, 1 F = 96500 C mol^-1]

Write the ionic equations for the oxidising action of potassium permanganate for its reaction with I^- (iodide) in both acidic and alkaline solutions.

From the given data of standard electrode potential E°_M²⁺/M values (in volts): Cr = -1.18, Mn = -1.18, Fe = -0.44, Co = -0.28, Ni = -0.25, Cu = +0.34, answer the following: (I) Why does E°_M²⁺/M show an irregular trend in the above values? (II) Why is E°_Cu²⁺/Cu value exceptionally positive? (III) Why is E°_Mn²⁺/Mn value highly negative?

Why do transition metals act as good catalysts?

Draw the structure of 'X' in the following reaction: a compound is treated with CrO₃ to give 'X'.

Name a member of the lanthanoid series: (I) which exhibits +4 oxidation state; (II) which exhibits +2 oxidation state.

Draw structure of the 2,4-dinitrophenylhydrazone derivative of benzaldehyde.

Arrange the following in increasing order of their reactivity towards HCN: Di-tert-butyl ketone, Acetaldehyde, Acetone.

Write the name of the reagent to convert Ethanenitrile to Ethanal.

Show how each of the following compounds can be converted to benzoic acid: (I) Acetophenone; (II) Ethyl benzene.

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

An organic compound (X) has the molecular formula C₅H₁₀O. Draw structures for (X) if it: (I) does not give Tollen's test but gives a positive iodoform test; (II) does not give Tollen's test and iodoform test but undergoes Aldol condensation; (III) undergoes Cannizzaro's reaction.

Write the reaction involved in the following:

Friedel-Crafts acylation of anisole

Give reason for the following:

Nucleophilic addition of ammonia and its derivatives does not occur with carbonyl group in strongly acidic medium.

Write the reaction involved in the following:

Reimer-Tiemann reaction

Compound 'X' with molecular formula \(C_4H_9Br\) reacts with aqueous KOH to give an alcohol. The rate of this reaction depends only on the concentration of the compound 'X'. When an optically active isomer 'Y' of the compound 'X' was treated with aqueous KOH solution, the rate of reaction was found to be dependent on concentration of compound 'Y' and aqueous KOH both.

(a) Write down the structural formula of both 'X' and 'Y'.

(b) Out of 'X' and 'Y', which one will undergo racemisation and why?

(c) Out of 'X' and 'Y', which one will form product with inversion of configuration and why?

Write the reaction involved in the following:

Kolbe's reaction

Calculate the boiling point of a solution containing 0.61 g of benzoic acid (Molar mass = 122 g mol\(^{-1}\)) in 5 g of \(CS_2\) in which it dimerises to the extent of 88%. The boiling point and \(K_b\) of \(CS_2\) are 46.2 \(^\circ C\) and 2.3 K kg mol\(^{-1}\) respectively.

What type of battery is Mercury cell? Why is it more advantageous than dry cell? Write overall reaction taking place in Mercury cell.

Give reason for the following:

Alpha (\(\alpha\)) hydrogens of aldehydes and ketones are acidic in nature.

Answer the following:

(i) Why is the Equilibrium Constant \(K_c\) related to \(E^\circ_{cell}\) and not to \(E_{cell}\)?

(ii) Two metals 'A' and 'B' have standard electrode potential values of \(-0.24\) V and \(+0.80\) V respectively. Which of these will liberate hydrogen gas from dil. \(H_2SO_4\)?

(iii) Write the cell reaction which occurs in lead storage battery when it is in charging.

Write the reactions of D-Glucose with the following:

(a) HI
(b) \(Br_2\) water
(c) Conc. \(HNO_3\)

Give reason for the following:

Carboxylic acids have higher boiling point than alcohols of comparable molecular masses.

For the first order thermal decomposition reaction, following data was obtained:

\(C_2H_5Cl(g) \rightarrow C_2H_4(g) + HCl(g)\)

[structure - image pending]

Calculate rate constant.
[Given: log 3 = 0.48]

(i) Give a chemical test to show that \([Co(NH_3)_5SO_4]Cl\) and \([Co(NH_3)_5Cl]SO_4\) are ionisation isomers.

(ii) What is meant by the 'Chelate effect'? Give an example.