Science (English Medium) Class 12 - CBSE Question Bank Solutions for Chemistry

Assertion (A): Chlorobenzene is resistant to electrophilic substitution reaction.

Reason (R): C-Cl bond in chlorobenzene acquires partial double bond characters due to resonance.

Four half-reactions, I to IV are shown below:

1. \[\ce{2Cl^- -> Cl2 + 2e^-}\]
2. \[\ce{4OH^- -> O2 + 2H2O + 2e^-}\]
3. \[\ce{Na^+ + e^- -> Na}\]
4. \[\ce{2H^+ + 2e^- -> H2}\]

Which two of these reactions are most likely to occur when concentrated brine is electrolysed?

In the two tetrahedral structures of dichromate ion, ______.

How can the activating effect of the −NH₂ group in aniline be controlled?

On the basis of Crystal Field theory, write the electronic configuration for the d⁵ ion with a strong field ligand for which Δ₀ > P.

Assertion (A): Bromination of benzoic acid, gives m-bromobenzoic acid.

Reason (R): Carboxyl group increases the electron density at the meta position.

On the basis of crystal field theory, write the electronic configuration for the d⁵ ion with a weak ligand for which Δ₀ < P.

Complete the reaction mentioning all the products formed:

\[\ce{2KMnO4 ->[\Delta]}\]

On the basis of crystal field theory, write the electronic configuration for d⁴ with a strong field ligand for which Δ₀ > P.

Complete the reaction mentioning all the products formed:

\[\ce{Cr2O^{2-}7 + 3H2S + 8H^+ ->}\]

Explain why the electrophilic substitution reactions in haloarenes occur slowly and require more drastic conditions as compared to those in benzene.

Read the passage carefully and answer the questions that follow.

Answer the following questions:

_(a) Out of ligands "A", "B", "C" and "D", which ligand causes maximum crystal field splitting? Why?

OR

Which of the two, “A” or “D” will be a weak field ligand? Why?

(b) Which of the complexes will be violet in colour? [CrA₆]^3- or [CrB₆]³⁺ and why?
(Given: If 560 - 570 nm of light is absorbed, the colour of the complex observed is violet.)

(c) If the ligands attached to Cr³⁺ ion in the complexes given in the table above are water, cyanide ion, chloride ion, and ammonia (not in this order).

Identify the ligand, write the formula and IUPAC name of the following:

1. [CrA₆]^3-
2. [CrC₆]³⁺

Which of the following ions will have a magnetic moment value of 1.73 BM.

\[\ce{Sc^3+, Ti^3+, Ti^2+, Cu^2+, Zn^2+}\]

Indicate the steps in the preparation of \[\ce{K2Cr2O2}\] from chromite ore.

Indicate the steps in the preparation of \[\ce{K2Cr2O7}\] from chomite ore.

Describe a method for refining nickel.

Indicate the steps in the preparation of \[\ce{K2Cr2O7}\] from chromite ore.

Describe a method for refining nickel.

Indicate the step in the preparation of K₂Cr₂O₇ from chromite ore.