Class 8: COAL AND PETROLEUM

Deekshita struggles to take down a pickle jar from the top shelf. Grandfather warns her it might break, but Deekshita replies it's an unbreakable plastic jar.

Grandfather recalls old clay jars. This sparks a realization of how materials have transformed over decades. The branch of science dealing with materials is called material science.

Activity-1 (Table 1): Comparison of materials used 30-40 years ago vs. today (e.g., clay pickle jars vs. plastic jars; copper/brass cooking vessels vs. stainless steel; coal/wood fuel vs. LPG).

Some materials like wood and gold have been used for thousands of years, while plastics are of recent origin.

Table 2 Sources: Glass from melted sand; clay from mineral kaolinite; wood from dried trees; plastics from petrochemicals; metals from ores.

Soil, water, air, and petrol obtained from nature are called natural resources.

Resources are classified into exhaustible (limited supply like coal, petroleum) and inexhaustible (abundant like air, solar energy, water).

Petroleum Depletion: From 1859 to 1969, world oil production reached 227 billion barrels (1 barrel = 159 litres). Half was produced in 100 years (1859-1959), and the next half in just 10 years (1959-1969). Consumption far exceeds formation rates.

Bio-diesel: Renewable, non-toxic alternative fuel made from plant oils or animal fat, though requiring arable land that might threaten food crop cultivation.

During the industrial revolution, coal-powered steam engines drove textile looms, trains, and ships. Coal met 50% of world electricity generation until 1950 before petroleum took over.

Over 4000 years ago, asphalt was used to waterproof Babylon walls. Ancestors used crude oil for boat waterproofing and lamps.

Natural Gas & CNG: Found trapped between impervious rocks. Stored under high pressure as Compressed Natural Gas (CNG). ONGC oversees exploration in Tripura, Mumbai High, KG Basin, and Jaisalmer.

Petroleum is a complex mixture separated by fractional distillation based on boiling point fractions.

Fractions include: Fuel gas (LPG), Petrol, Kerosene, Diesel oil, Lubricating oil, Fuel oil, Paraffin wax, and Asphalt (Bitumen) residue used for road surfacing.

Heating coal yields three main products:

1. Coke: Tough, porous, black, nearly pure carbon used in steel manufacturing and metal extraction.
2. Coal Tar: Thick black liquid mixture of ~200 substances used for synthetic dyes, explosives, perfumes, and naphthalene balls.
3. Coal Gas: Used as industrial fuel near processing units.

Lab Activity: Heating powdered coal in a hard boiling tube. Brownish-black vapours pass through a water-filled second tube, producing colourless gas bubbles. When ignited at the jet nozzle, the evolved coal gas burns with a bright flame, proving volatile gases are trapped within coal.

Petrochemicals: Useful substances obtained from petroleum and natural gas (detergents, synthetic fibres like nylon and polyester). Due to immense commercial value, petroleum is called liquid gold.

Table 6 outlines petrochemical applications across agriculture, industry, and domestic life (plastics, medicines, cosmetics, tyres).

Coal Formation (Carbonisation): Dense forest wetlands buried under soil by floods/earthquakes over millions of years underwent high pressure and temperature to convert into carbon-rich coal.

Petroleum Formation: Formed from tiny sea organisms called **plankton** settling at ocean floors, covered with sand/clay, and transformed under absence of air, high heat, and pressure.

Fossil fuels are strictly limited. Conserving them requires avoiding unnecessary wastage (e.g., using electric washing machine dryers when sunlight is abundant, riding motorbikes for short distances instead of walking/bicycles).

Activity-5: Group discussions on misuse of fuels in transport, cooking, and industry.