Science class online
Chemistry and physics lessons
atom physics lesson


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

Science class




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

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

Most common metals

How to distinguish metals ?

Corrosion of metals

Electrical conductivity of solid materials

Electrons and free electrons

Electric current in metals
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


Mixtures and solutions

Dissolving a solid in water

1) What is a dissolution ?

When a solid forms a homogeneous mixture with water it is said that:
- The solid dissolves in water.
- The solid is soluble in water.
Examples: salt, sugar, cocoa powder are soluble in water.

When a solid dissolves in water it is reduced to fine particles invisible to the naked eye which are dispersed in water.


The mixture obtained in a dissolution is called an aqueous solution.
The water used to dissolve the solid is called a solvent.
The solid which is dissolved is called a solute.

- There are non-aqueous solutions obtained with other solvents such as alcohol.
- The solids dissolved in water does not change state. These solids have just been reduced in particles that are too small to be seen with the naked eye.
2) Saturation of a solution

IThere is a limit to the amount of solid that can be dissolved in a volume of water.
When this limit is reached, we say that the solution is saturated.

As long as the saturation limit is not reached the solid added in water can be dissolved.
When the saturation limit is reached the solid no longer dissolves and remains visible.