RESOURCES -SCANNED TBk NOTES-HYDROGEN-2024-25

Hydrogen: An Overview

First Element Formed

• Hydrogen was the first element formed after the universe was created and is the simplest atom, weighing about one-fourteenth as much as an equal volume of air.

Role in the Sun

• Provides energy through the nuclear fusion of hydrogen nuclei, producing sunlight and heat.

Discovery of Hydrogen

Early Observations

• Swiss physician Paracelsus (16th century) noted inflammable gas from iron and sulfuric acid.

• Robert Boyle (1672) first to collect and measure combustion.

• Henry Cavendish (1766) obtained it by adding sulfuric acid to zinc, called it inflammable, and discovered its formation of water.

Naming

• Antoine Lavoisier (1783) named it hydrogen, meaning 'water former'.

Occurrence of Hydrogen

Abundance

• 9th most abundant element in Earth's crust at almost 1%.

• Present in both free and combined states (e.g., in water, organic matter such as coal and petroleum).

Celestial Presence

• Free hydrogen exists in the Sun and between stars.

Importance of Hydrogen

Chemical Properties

• Inflammable, high heat of combustion, reducing property.

Applications

• Used in fuels, metallurgy, hydrogenation processes (turning oils into solid fats).

General Methods of Preparation

Actions with Water

• Metals like potassium, sodium, and calcium react with cold water.Example:2Na + 2H₂O → 2NaOH + H₂↑

Reactions with Steam

• Magnesium, zinc, aluminum, and iron produce hydrogen with steam:3Fe + 4H₂O → Fe₃O₄ + H₂↑

Acid Reactions

• Dilute acids react with metals above hydrogen in the activity series (e.g., zinc and hydrochloric acid).

Laboratory Preparation of Hydrogen

• Procedure: Use zinc granules and dilute sulfuric/hydrochloric acid in a flask to collect hydrogen (reaction is exothermic).

• Collection: Collected by downward displacement of water after allowing hydrogen gas to escape air.

Hazards and Safety Precautions

• Inflammability: Ensure apparatus is airtight, collect gas free from air, and keep away from flames to prevent explosions.

Tests for Hydrogen

Physical Properties

• Colourless, odourless, neutral gas; burns in oxygen with a pale blue flame; produces a loud pop sound.

Chemical Properties of Hydrogen

• Neutral Gas: No effect on litmus paper.

• Reaction with Chlorine: In direct sunlight, forms HCl explosively.

• Reaction with Non-Metals: Burns but does not support combustion.

Industrial Preparation of Hydrogen

Processes

• Water gas method (pass superheated steam over heated coke).

• Electrolysis of acidulated water in a Hofmann Voltameter yields hydrogen and oxygen in a ratio of 2:1.

Uses of Hydrogen

Fuel

• High heat of combustion, component of gaseous fuels.

Synthesis

• In the production of ammonia, hydrochloric acid, and synthetic petrol through hydrogenation.

Oxy-Hydrogen Torch

• Used for welding and cutting metals.

Metallurgy

• Reduces metal oxides to metals at high temperatures.