1. Position of Hydrogen in the Periodic Table
Hydrogen is the lightest element and holds a unique position in the periodic table. It can be placed in two groups because its properties are similar to both:
- Group 1 (Alkali Metals): Like alkali metals, hydrogen has one valence electron and can form a positive ion (H+) by losing this electron.
- Group 17 (Halogens): Like halogens, it needs only one electron to complete its outermost shell and can form a negative ion (H−) by gaining an electron. It also exists as a diatomic molecule (H2).
Due to these dual properties, hydrogen is often placed in a separate position at the top of the periodic table.
2. Laboratory Preparation of Hydrogen 🧪
Hydrogen gas is typically prepared in the laboratory by reacting a metal with a dilute acid. A common method involves reacting granulated zinc with dilute hydrochloric acid (HCl) or dilute sulfuric acid (H2SO4).
- Reactants: Granulated zinc (Zn) and dilute hydrochloric acid (HCl).
- Apparatus: A conical flask, thistle funnel, delivery tube, and gas jar.
- Reaction:Zn+2HCl→ZnCl2+H2
- Drying: The hydrogen gas is passed through a drying agent like anhydrous calcium chloride or concentrated sulfuric acid to remove moisture.
- Collection: The gas is collected by the downward displacement of water because it’s virtually insoluble in water and is lighter than air.
3. Industrial Preparation of Hydrogen
Large quantities of hydrogen are produced industrially by various methods:
- From Water Gas: Water gas (a mixture of carbon monoxide and hydrogen) is produced by passing steam over red-hot coke. The carbon monoxide is then oxidized to carbon dioxide with more steam, and the hydrogen is separated.C+H2O=CO+H2 (Water gas)
- From Natural Gas (Methane): A common method is the steam reforming of methane in the presence of a nickel catalyst.CH4+H2O=CO+3H2
- Electrolysis of Water: This method produces very pure hydrogen. Water is acidified with a little acid to increase its conductivity. Hydrogen is produced at the cathode and oxygen at the anode in a 2:1 volume ratio.
4. Chemical Properties of Hydrogen
- Combustion: Hydrogen is highly combustible and burns in air with a pale blue flame to form water. This reaction is highly exothermic.2H2+O2=2H2O
- Reducing Property: Hydrogen is a powerful reducing agent as it can remove oxygen from metal oxides. For example, when passed over heated copper(II) oxide, it reduces the oxide to copper and forms water.CuO+H2=Cu+H2O
- Reaction with Halogens: Hydrogen reacts with halogens to form hydrogen halides. The reaction with fluorine is explosive even in the dark, while the reaction with chlorine is explosive in sunlight.H2+Cl2= 2HCl
- Hydrogenation: Hydrogen adds across double or triple bonds in unsaturated organic compounds in the presence of a catalyst (like nickel) to form saturated compounds.CH2=CH2+H2=CH3−CH3
5. Uses of Hydrogen
- Haber Process: It is used in the synthesis of ammonia, which is a key component of fertilizers.
- Hydrogenation: Used for the hydrogenation of vegetable oils to produce solid fats (vanaspati ghee).
- Fuel: Liquid hydrogen is used as a rocket fuel.
- Metallurgy: Used as a reducing agent in the extraction of metals from their oxides.
- Welding: Oxy-hydrogen flames, which produce intense heat, are used for cutting and welding metals.
