Air Composition and Oxygen

• Air comprises a mixture of gases.
• Dry air's approximate composition includes nitrogen, oxygen, argon, carbon dioxide, and trace gases with variable water vapor amounts.
• Oxygen is essential for respiration and combustion.
• Oxygen is crucial for supporting life in animals and combustion.

Air Composition

• Nitrogen (78%) is the most abundant and mainly inert gas.
• Oxygen (21%) is essential for respiration and combustion.
• Argon (1%) is an inert noble gas.
• Carbon dioxide (0.04%) is important for photosynthesis and as a greenhouse gas.

Phlogiston Theory

• Scientists believed in the Phlogiston Theory before discovering oxygen.
• Phlogiston was thought to be a substance in all combustible materials.
• Burning materials release phlogiston, according to the theory.
• Candle burning releases phlogiston; wood turning to ash means phlogiston escaped.
• Metals gain mass when burned, disproving the theory that burning releases mass.

Antoine Lavoisier

• In the 1770s, Lavoisier disproved the Phlogiston Theory.
• Combustion and rusting require a specific gas from the air.
• Oxygen increases mass, showing something is added during combustion, not lost.
• Lavoisier named the gas "oxygen," which means "acid producer".
• Lavoisier proved water is made of oxygen and hydrogen and developed the modern definition of elements.
• He established the Law of Conservation of Mass, stating that matter cannot be created or destroyed.

Gas Uses

• Oxygen is used in medical breathing support, welding, and rocket fuel.
• Nitrogen is used to make fertilizers, in food packaging, and as a coolant (liquid nitrogen).
• Argon is used in light bulbs and for welding.
• Carbon dioxide is used in fizzy drinks, fire extinguishers, and photosynthesis.

Classifying Oxides

• Acidic oxides, formed by non-metals, dissolve in water to form acids (e.g., CO₂ forms carbonic acid, SO₂ forms sulfuric acid).
• Basic oxides, formed by metals, dissolve in water to form bases (e.g., calcium oxide forms limewater).
• Neutral oxides are neither acidic nor basic, such as carbon monoxide (CO) and water (H₂O).

Fire Triangle

• A fire includes oxygen (supports combustion), heat (energy to start), and fuel (the substance that burns).
• Removing any element stops the fire.
• Fuel is any burnable material that releases energy.

Combustion

• Complete combustion occurs with plenty of oxygen, producing carbon dioxide and water.
• Incomplete combustion occurs when oxygen is limited, producing carbon monoxide (toxic gas) and soot (carbon particles).
• Incomplete combustion will also release less energy.

Burning Fossil Fuels

• Fossil fuels (coal, oil, and gas) contain carbon, hydrogen, and sulfur.
• Burning produces carbon dioxide (CO₂), a greenhouse gas contributing to global warming.
• Carbon monoxide (CO) is a poisonous gas that reduces oxygen in the blood.
• Sulfur dioxide (SO₂) forms acid rain, which damages forests and buildings.
• Nitrogen oxides (NOx) contribute to smog and acid rain

Alternative energy

• Renewable energy sources do not run out and are environmentally friendly.
• Solar energy converts sunlight into electricity
• Wind energy utilizes wind turbines to generate electricity
• Hydroelectric power uses flowing water to generate power
• Geothermal energy uses heat from the Earth's core
• Renewable sources reduce dependence on fossil fuels and decrease pollution.

Rusting

• Rusting occurs when iron reacts with oxygen and water to form iron oxide.
• Rusting is prevented by painting/coating (prevents air and water contact), galvanizing (coating with zinc), or using oil/grease (prevents water from reaching the metal).

Variables

• The independent variable is the factor you change in an experiment.
• The dependent variable is the factor you measure in response.

Data Reliability

• A larger sample size reduces errors and improves accuracy.
• Repeating experiments and averaging results ensures reliability.