The D and F Block Elements — Class 12 Chemistry NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 12 Chemistry chapter "The D and F Block Elements" — 6 important questions with detailed answers for CBSE board exam preparation.
✓ 100% Free
✓ No Login Needed
✓ NCERT / CBSE Aligned
✓ Download as PDF
TL;DR: Free step-by-step NCERT solutions for Class 12 Chemistry chapter "The D and F Block Elements" — 6 important questions with detailed answers for CBSE b…
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
🤖 Stuck on any question? Ask Syllab's free AI Tutor for a step-by-step explanation — instant, unlimited, no login.
Key Questions Covered:
- Define transition elements. What are the characteristic properties of transit…
- Compare the properties of Cr and Mn. Why do they differ?
- Discuss the chemistry of potassium permanganate (KMnO₄). What is its structur…
- Write the electronic configuration of Zn²⁺ and explain why zinc is not consid…
- Explain the lanthanide contraction and its consequences.
- Write the preparation and properties of potassium dichromate (K₂Cr₂O₇).
Solutions Summary:
| Question | Status |
|---|---|
| Define transition elements. What are the characteristic p… | ✓ Solved |
| Compare the properties of Cr and Mn. Why do they differ? | ✓ Solved |
| Discuss the chemistry of potassium permanganate (KMnO₄). … | ✓ Solved |
| Write the electronic configuration of Zn²⁺ and explain wh… | ✓ Solved |
| Explain the lanthanide contraction and its consequences. | ✓ Solved |
| Write the preparation and properties of potassium dichrom… | ✓ Solved |
Showing 6 of 6 questions
Q1: Define transition elements. What are the characteristic properties of transition metals?
Transition Elements:
Elements with incompletely filled d-orbitals in their atoms or cations, or those with tendency to form ions by loss of electrons from d-orbitals.
They occupy the d-block of periodic table (Groups 3-12, Periods 4-6).
Characteristic Properties:
1. Variable Oxidation States:
Multiple oxidation states due to similar energies of (n-1)d and ns electrons.
Example: Manganese shows oxidation states from +2 to +7
Cr: +2, +3, +6; Mn: +2, +3, +7; Fe: +2, +3; Cu: +1, +2
2. Formation o...
Q2: Compare the properties of Cr and Mn. Why do they differ?
Chromium (Cr) vs Manganese (Mn):
Both are in Period 4 of d-block. Electron configurations:
Cr: [Ar] 3d⁵ 4s¹ (half-filled d-orbital)
Mn: [Ar] 3d⁵ 4s² (half-filled d-orbital + filled s-orbital)
Comparison:
Property | Chromium | Manganese
---------|----------|----------
Atomic number | 24 | 25
Electron config | 3d⁵4s¹ | 3d⁵4s²
Half-filled | Half-filled 3d | Half-filled 3d
Common oxidation states | +2, +3, +6 | +2, +3, +7
Most stable oxidation state | +3 | +2
Meeting point (K) | 2180 | 1519
Densit...
Q3: Discuss the chemistry of potassium permanganate (KMnO₄). What is its structure and oxidizing properties?
Potassium Permanganate (KMnO₄):
Structure:
Molecular formula: KMnO₄
Ionic compound containing K⁺ and MnO₄⁻ ions
MnO₄⁻ ion structure (tetrahedral):
1. Mn is in +7 oxidation state
2. Four oxygen atoms surround Mn (tetrahedral arrangement)
3. Oxygen atoms form covalent bonds with Mn
4. Total charge: -1 (MnO₄⁻ is tetravalent anion)
5. Mn: [Ar] 3d⁰ (all d-electrons transferred to oxygen ligands)
Physical Properties:
1. Appearance: Dark purple/violet crystals
2. Soluble in water: Yes, readily solub...
Q4: Write the electronic configuration of Zn²⁺ and explain why zinc is not considered a typical transition metal despite being in d-block.
Zinc (Zn) Electronic Configuration:
Zn (neutral): [Ar] 3d¹⁰ 4s²
Atomic number: 30
Zn²⁺ (ion): [Ar] 3d¹⁰
Zn²⁺ loses both 4s electrons: 3d¹⁰ 4s² → 3d¹⁰ + 2e⁻
Why Zn is NOT a typical transition element:
1. Completely Filled d-orbitals:
Zn²⁺ has completely filled d-orbitals (d¹⁰), no unpaired electrons
Typical transition metals have incompletely filled d-orbitals with unpaired electrons
2. Lacks Variable Oxidation States:
Zn shows only +2 oxidation state (loses 4s² electrons)
No other stable ox...
Q5: Explain the lanthanide contraction and its consequences.
Lanthanide Contraction:
The phenomenon of gradual decrease in atomic and ionic radii of lanthanide elements from La to Lu, despite increase in atomic number and addition of electrons to same 4f subshell.
Cause:
As atomic number increases from La (Z=57) to Lu (Z=71):
1. Each additional electron enters the 4f orbital (inner orbital, not valence)
2. Electrons in diffuse f-orbitals provide poor shielding effect
3. Nuclear charge increases by 1 for each new electron
4. Net effect: Strong increase in...
Q6: Write the preparation and properties of potassium dichromate (K₂Cr₂O₇).
Potassium Dichromate (K₂Cr₂O₇):
Preparation:
Laboratory Method:
1. Chromite ore (FeCr₂O₄) is roasted with Na₂CO₃ at high temperature:
4FeCr₂O₄ + 8Na₂CO₃ + 7O₂ → 8Na₂CrO₄ + 2Fe₂O₃ + 8CO₂
2. Sodium chromate (Na₂CrO₄) solution is obtained and acidified with H₂SO₄:
2CrO₄²⁻ + 2H⁺ → Cr₂O₇²⁻ + H₂O
(Yellow) → (Orange)
3. Cool the solution and add KCl to precipitate K₂Cr₂O₇:
Na₂CrO₇²⁻ + 2K⁺ + Cl⁻ → K₂Cr₂O₇↓ + 2NaCl
4. Filter, wash with cold water, and dry.
Alternative Method:
From potassium chromat...
Showing 6 of 6 questions. Visit the full page for complete solutions.
More Class 12 Chemistry NCERT Solutions
- Solutions — Class 12 Chemistry NCERT Solutions
- Electrochemistry — Class 12 Chemistry NCERT Solutions
- Chemical Kinetics — Class 12 Chemistry NCERT Solutions
- Coordination Compounds — Class 12 Chemistry NCERT Solutions
- Haloalkanes and Haloarenes — Class 12 Chemistry NCERT Solutions
- Alcohols Phenols and Ethers — Class 12 Chemistry NCERT Solutions
- Aldehydes Ketones and Carboxylic Acids — Class 12 Chemistry NCERT Solutions
- Amines — Class 12 Chemistry NCERT Solutions
- Biomolecules — Class 12 Chemistry NCERT Solutions