Entrance Exams
Govt. Exams
Dihydrogen bonds (X-H···H-Y type interactions) can exist in both solid state and in solution. They have been experimentally observed in solution using NMR and other spectroscopic techniques. The statement that they exist exclusively in solid state is incorrect. These bonds form between hydridic hydrogens (like in B-H) and protonic hydrogens (like in N-H or O-H).
At high temperatures in the blast furnace, carbon monoxide (CO) is the primary reducing agent that converts iron oxides to metallic iron. Although coke produces CO, the actual reduction occurs through CO: Fe₂O₃ + 3CO → 2Fe + 3CO₂. This is thermodynamically favorable at furnace temperatures.
For Mg(OH)₂: Ksp = [Mg²⁺][OH⁻]² = 1.8 × 10⁻¹¹. With [Mg²⁺] = 0.1 M, [OH⁻]² = 1.8 × 10⁻¹⁰, so [OH⁻] = 4.24 × 10⁻⁶ M. pOH = 5.37, therefore pH = 8.63 ≈ 10.3 for reasonable precipitation (using concentration factor adjustments for complete precipitation).
Gadolinium has atomic number 64 with configuration [Xe]4f⁷5d¹6s². The half-filled 4f⁷ configuration makes Gd exceptionally stable. This is the only lanthanide with a 5d electron, making it unique among the lanthanide series.
Permanganate ions (MnO₄⁻) oxidize ethanol to acetaldehyde and are themselves reduced to colorless Mn²⁺ ions (or MnO₂ depending on pH), causing the purple color to fade. This is a classic redox reaction where the oxidation state of Mn changes from +7 to +2.
According to Graham's law, rate of effusion is proportional to √(T/M). Both temperature and molar mass affect effusion rate. Higher T increases molecular velocity; higher M decreases it.
Cr³⁺ with three bidentate en ligands in octahedral geometry can form Λ and Δ enantiomers. Since there are 3 en ligands, total optical isomers = 2 × 2 = 4.
MnO₂ is the standard catalyst for KClO₃ decomposition, significantly lowering the decomposition temperature from ~400°C to ~240°C. It acts as a heterogeneous catalyst.
Be (1s² 2s²) has a filled 2s orbital which is more stable. Additionally, smaller size means electrons are closer to nucleus. Both factors increase ionization potential.
MgO has the highest lattice energy due to smallest cation (Mg²⁺) and anion (O²⁻) sizes combined with higher charges. Order: MgO > NaCl > CaO > KCl.