Chemistry

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

 

Atoms and molecules


Molecules in mixtures and pure substances


The concept of molecule allows to give a more precise definition of mixtures and pure substances.
 
1) Pure substances

A pure substance is a substance (solid, liquid or gas) that consists only of one kind of molecule.

examples:
- Distilled water is a pure substance because it consists only of water molecules.
- Dioxygen is a pure substance because it consists only of dioxygen molecules

2) Mixtures

A mixture is a substance (solid, liquid or gas) which consists of several kinds of molecules.

examples:
- Air is a mixture because it consists of several kinds of molecules: dioxygen, dinitrogen, carbon dioxide etc..
- The sugar water is a mixture because it consists of two kinds of molecules: water and sugar (saccharose).





Science class

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
Volumetric mass density

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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