CHEMCA
EXAM MASTER REVIEW SHEET
Hydrogen and its Compounds
Core Review for JEE Main, Advanced & NEET
1. Position & Isotopes
Hydrogen is the first element, showing resemblance to both Alkali metals (Gr 1) and Halogens (Gr 17).
| Isotope | Symbol | Composition | Remarks |
|---|---|---|---|
| Protium | \(^1_1H\) | \(1p, 0n\) | Most abundant |
| Deuterium | \(^2_1H\) (D) | \(1p, 1n\) | Used as moderator |
| Tritium | \(^3_1H\) (T) | \(1p, 2n\) | Radioactive (\(\beta^-\) emitter) |
2. Industrial Preparation
Water Gas Shift Reaction:
\[ \underbrace{CO + H_2}_{\text{Syn-gas}} + H_2O(g) \xrightarrow[473K]{FeCrO_4} CO_2(g) + 2H_2(g) \]
CO is removed by scrubbing with Sodium Arsenite.
Coal Gasification:
\[ C(s) + H_2O(g) \xrightarrow{1270K} CO(g) + H_2(g) \]Lane's Process:
\[ 3Fe + 4H_2O \rightleftharpoons Fe_3O_4 + 4H_2 \]3. Classification of Hydrides
Ionic (Saline)
s-block elements (except Be, Mg). High M.P., crystalline solids.
Molecular
p-block elements. Electron deficient (Gr 13), Precise (Gr 14), Rich (Gr 15-17).
Metallic
d and f-block. Non-stoichiometric. "Hydride Gap" exists in Gr 7, 8, 9.
4. Hardness of Water
Temporary Hardness
Due to \(Ca/Mg\) Bicarbonates.
Removal: Boiling or Clark's Method (Lime).
Permanent Hardness
Due to \(Ca/Mg\) Chlorides & Sulphates.
Removal: Calgon, Ion-exchange (Zeolites/Resins).
Hardness Calculation (ppm):
\[ \text{Hardness in ppm} = \frac{\text{Mass of } CaCO_3 \text{ equiv.}}{\text{Total mass of Water}} \times 10^6 \]
1 mole Bicarbonate \(\equiv\) 1 mole \(CaCO_3\)
5. Hydrogen Peroxide Essentials
Structure
Non-planar, "Open-book" structure.
Dihedral angle: \(111.5^\circ\) (Gas) | \(90.2^\circ\) (Solid)
Preparation
\[ \text{2-ethylanthraquinol} \xrightarrow[O_2]{\text{air}} H_2O_2 \]
Strength Calculations:
Molarity Relation
\[ \text{Volume Strength} = 11.2 \times M \]
Normality Relation
\[ \text{Volume Strength} = 5.6 \times N \]
Storage: \(H_2O_2\) decomposes in light; stored in wax-lined glass or plastic bottles in dark. Urea is added as a stabilizer.
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