Sources and Discovery of Hydrogen
Hydrogen is the lightest substance known and the most abundant element in the universe. It has a mass of just 0.09 g per litre at normal temperature and pressure. Though it is present in abundance in celestial bodies, like the sun and stars, it is not present in a free state in our atmosphere. Hydrogen is present in the combined form in many substances, like water, acids, alkalis, hydrocarbons, carbohydrates, fats and oils, proteins, cellulose, etc.
Position of Hydrogen in the Periodic Table
Hydrogen is the first element of the periodic table. Its atomic number is 1, which indicates the presence of only one electron in the atom of hydrogen. This electron is present in its first shell. Hydrogen resembles both alkali metals (group I A) as well as halogens (group VII A) therefore its position is said to be anomalous.
Preparation of Hydrogen
Hydrogen can be prepared from cold water, steam, acids and alkalis.
From cold water
Highly electropositive metals like potassium, calcium and sodium combine with cold water, even ice-cold water to give their respective hydroxides and hydrogen.
Industrial Preparation of Hydrogen by Bosch process
Industrial hydrogen is prepared with the help of coke, air and water. Coke is packed into a huge furnace or chamber, and very hot air is passed through for some time. The oxygen of the air combines with the coke to form carbon dioxide, liberating huge amount of heat, i.e., it is an exothermic reaction.
Physical Properties of Hydrogen
1. A colourless, odourless and tasteless gas.
2. Non-poisonous.
Chemical Properties of Hydrogen
Reaction with litmus paper
Hydrogen is neutral to litmus. When we introduce wet blue and red litmus paper into a jar of hydrogen, no change of color is noticed.
Tests for Hydrogen
1. Burns in air, with a pale blue flame, to form only water.
2. Lighter than air- lightest substance known, rises always high.
Uses of Hydrogen
As a fuel
Hydrogen has a high calorific value, and as such, is an ideal fuel. It has a high calorific value. It is also 100% pollution free, as the only product formed on combustion is water vapour. Many gaseous fuels such as, water gas, coal gas, etc. contain comparatively high percentage of hydrogen.
Summary
Hydrogen is absent in the free state in the earth's atmosphere. But in the combined state it is found in water, acids, alkalis, carbohydrates, fats, oils, proteins, cellulose etc.
