Hydrogen and Its Compounds – JEE Chemistry
1. Position of Hydrogen in the Periodic Table
Hydrogen is the first element of the periodic table with atomic number 1.
It shows similarities with both alkali metals (Group 1) and halogens (Group 17).
Hydrogen is placed separately because of its unique properties.
2. Isotopes of Hydrogen
| Isotope | Symbol | Neutrons |
|---|---|---|
| Protium | $^1H$ | 0 |
| Deuterium | $^2H$ or $D$ | 1 |
| Tritium | $^3H$ or $T$ | 2 |
Deuterium is widely used in nuclear reactors.
3. Preparation of Hydrogen Gas
(a) Laboratory Preparation
$Zn + 2HCl \rightarrow ZnCl_2 + H_2 \uparrow$
(b) Industrial Preparation
$CH_4 + H_2O \rightarrow CO + 3H_2$ (Steam reforming)
$CO + H_2O \rightarrow CO_2 + H_2$ (Water gas shift reaction)
4. Physical Properties of Hydrogen
- Colourless, odourless, tasteless gas
- Lightest element
- Highly inflammable
5. Chemical Properties of Hydrogen
(a) Combustion
$2H_2 + O_2 \rightarrow 2H_2O$
(b) Reducing Nature
$CuO + H_2 \rightarrow Cu + H_2O$
6. Hydrides
Hydrides are binary compounds of hydrogen with other elements.
| Type | Example |
|---|---|
| Ionic Hydrides | $NaH, CaH_2$ |
| Covalent Hydrides | $CH_4, NH_3$ |
| Metallic Hydrides | $TiH_2$ |
7. Water – Structure and Properties
Water is a bent molecule with bond angle of $104.5^\circ$.
Hydrogen bonding causes high boiling point of water.
8. Hardness of Water
| Type | Cause |
|---|---|
| Temporary | $Ca(HCO_3)_2, Mg(HCO_3)_2$ |
| Permanent | $CaCl_2, MgSO_4$ |
9. Hydrogen Peroxide ($H_2O_2$)
Preparation
$BaO_2 + H_2SO_4 \rightarrow BaSO_4 + H_2O_2$
Structure
Non-planar molecule with open book structure.
10. Properties of Hydrogen Peroxide
As Oxidising Agent
$PbS + 4H_2O_2 \rightarrow PbSO_4 + 4H_2O$
As Reducing Agent
$H_2O_2 + O_3 \rightarrow H_2O + 2O_2$
11. Uses of Hydrogen
- Fuel cells
- Manufacture of ammonia
- Hydrogenation of oils
12. Uses of Hydrogen Peroxide
- Bleaching agent
- Antiseptic
- Rocket propulsion
13. Heavy Water ($D_2O$)
Heavy water contains deuterium instead of hydrogen.
Used as moderator in nuclear reactors.
14. Comparison of Water and Heavy Water
| Property | $H_2O$ | $D_2O$ |
|---|---|---|
| Boiling Point | $100^\circ C$ | $101.4^\circ C$ |
| Density | 1.0 | 1.1 |
15. Important JEE Points
- Hydrogen shows both oxidation states +1 and −1
- Hydrogen bonding affects boiling point
- $H_2O_2$ acts as both oxidising and reducing agent