Air & Flames

Air is a mixture of gases, mainly nitrogen and oxygen, with small amounts of carbon(IV) oxide, noble gases, and water vapour. These components can be separated by physical means. Nitrogen makes up about 4/5 of the atmosphere by volume, while oxygen accounts for about 1/5.

Properties of Air

1. Water Vapour in Air

Water vapour enters the atmosphere through the evaporation of oceans, rivers, lakes, seas, and reservoirs. The amount of moisture in the air varies depending on temperature, weather, and location.

2. Noble Gases in Air

Argon is the most abundant noble gas in air, followed by neon. Noble gases are generally unreactive and are used in advertising lights for their bright colours.

3. Carbon(IV) Oxide in Air

The presence of carbon(IV) oxide can be detected by passing air through limewater (calcium hydroxide solution) or potassium hydroxide solution. The balance of carbon(IV) oxide in the atmosphere is maintained through respiration and photosynthesis.

4. Oxygen in Air

Oxygen is the most reactive component of air and supports life. It is involved in processes like combustion, corrosion (rusting), and respiration.

Corrosion

Corrosion is the deterioration of metals when exposed to air over time. Rusting is the corrosion of iron and can be prevented by:

• Applying grease
• Painting exposed surfaces
• Coating with other metals like chromium

Air Pollution

Air pollution occurs when harmful substances are released into the atmosphere in significant quantities, posing risks to living things.

Causes of Air Pollution

• Burning of fossil fuels like coal, gasoline, and petroleum gases
• Release of freons from aerosol cans
• Emission of poisonous gases during chemical warfare

Air Pollutants

1. Particulate Matter

Particulate matter consists of tiny solid particles like dust, smoke, soot, asbestos, and heavy metals (lead, cadmium, arsenic, mercury). Long-term exposure can lead to brain damage, irritability, aggressive behaviour, and gastric issues.

2. Oxides of Carbon

Carbon(II) oxide is produced from the incomplete burning of fossil fuels. It binds with haemoglobin, preventing oxygen transport in the body, leading to brain damage or death. Carbon(IV) oxide traps heat in the atmosphere, causing the greenhouse effect.

3. Oxides of Sulphur and Nitrogen

Burning coal and refining petroleum release sulphur(IV) oxide, which oxidizes to sulphur(VI) oxide and falls as acid rain. Effects include:

• Respiratory problems
• Damage to plants
• Corrosion of metals and buildings, and damage to fabrics and leather

Nitrogen(II) oxide depletes the ozone layer, while nitrogen(IV) oxide contributes to acid rain.

4. Gaseous Hydrocarbons and Chlorofluorocarbons (CFCs)

Volatile hydrocarbons like methane can cause cancer and contribute to the greenhouse effect. CFCs destroy the ozone layer, exposing the Earth to harmful ultraviolet rays that cause skin cancer and other health issues.

Flames

Flames are produced when substances burn. A flame is the region where gases react chemically, producing heat and light. Flames can be either luminous (bright and yellow) or non-luminous (barely visible).

Types of Flames

Hydrogen Flame

Hydrogen burns with a faint, non-luminous flame. It consists of two zones: the unburnt gas zone and the complete combustion zone.

Candle Flame

A candle produces a luminous flame with four identifiable zones:

• The zone of unburnt gas around the wick
• The bright yellow luminous zone where incomplete combustion occurs
• The barely visible non-luminous zone where complete combustion happens
• The blue zone at the base, indicating complete combustion

Bunsen Flame

A Bunsen burner mixes air with fuel gas (mainly methane, butane, hydrogen, and carbon(II) oxide) to produce flames for laboratory use.

Luminous Bunsen Flame

Produced when the air hole is closed. The flame is high, bright, wavy, yellow, and relatively cooler.

Non-Luminous Bunsen Flame

Produced when the air hole is open. This flame is hotter, cleaner, and more compact compared to the luminous flame.