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Chemistry

Free online chemistry lesson for elementary school, middle school and high school.
chemistry high school
 

Science class

Chemistry

Electricity

Optics

Mechanics
Mechanics lessons
Water
Water on Earth
Changes of state in the nature: the water cycle
Water in human body
Test for water
Properties of water in different states
States of matter
States of matter and its changes
Boiling water
Water: freezing and melting
Changes of state: mass and volume
Molecules in different states of matter

Mixtures and solutions
Heterogeneous mixtures
Homogeneous mixtures
Decantation
Centrifugation
Filtration
Vaporization of water
Distillation
Chromatography
Dissolving a solid in water
Conservation of mass on dissolving
Miscibility in water

Mass and volume
Volume and its units
Measuring volume with a graduated cylinder
Mass and its units
Measuring the mass of a liquid
Mass of a liter of water

Air and atmosphere
Atmosphere
Earth's atmosphere protect us
Threats to the Earth's atmosphere
Composition of air
Air and life
Pressure
Atoms and molecules
Molecules
Molecules in mixtures and pure substances
Molecules and states of matter
Atoms
Composition of molecules
Constituents of the atoms
The electrical neutrality of the atom

Combustions
Basics of combustion
The combustion of carbon
The combustion of butane
Atoms and chemical reactions
Chemical reactions
Chemical equations
Law of conservation of mass
Chemical synthesis
Metals

Most common metals

How to distinguish metals ?

Corrosion of metals

Electrical conductivity of solid materials

Electrons and free electrons

Electric current in metals
Ions
The conductivity of aqueous solutions
Aqueous solutions and ions
The direction of movement of ions
Formation of ions
Tests for ions
Acidic and basic solutions
pH of aqueous solutions
Ions in acidic and basic solutions
Dilution of acids and bases
Composition of hydrochloric acid
Chemical reaction between iron and hydrochloric acid

Electrochemical cells and chemical energy
Chemical reaction beteween a copper sulphate solution and zinc
Copper sulfate and zinc battery
Basics of electrochemical cell



















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Air and atmosphere

Atmosphere

 
1) What is an atmosphere ?

Definition of an atmosphere: this is a layer of gases surrounding a celestial body.

Examples of celestial bodies that have an atmosphere: Earth, Mars, Venus, Jupiter, the Sun, Titans.
Examples of celestial bodies with no atmosphere: the Moon, Mercury, Pluto.

Comment: The presence of an atmosphere around a celestial body doesn't systematically means that it can sustain life.
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2) Characteristics and layers of Earth's atmosphere.

The Earth's atmosphere is the layer of air surrounding the Earth.
Its thickness is estimated at about 500 km.


Temperature variations in Earth's atmosphere are not regular. In some areas it decreases and it increases in others. This leads to distinguish several layers:
- The troposphere from 0 to (on average) 12 km in altitude. The temperature decreases with altitude. The troposphere contains about 90% of the air.
- The stratosphere extends roughly from 12 to 50 km altitude. The temperature is steadily increasing.
- The mesosphere extends roughly from 50 to 80 km altitude. The temperature is steadily increasing.
- Thermosphere extends  roughly from 80 to 500 km


Comment: sometimes an additional layer called the exosphere is included in atmosphere. Exosphere is a transition area  to interplanetary space that it is still protected from particles emitted from the Sun, by the Earth's magnetic field.
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