Learning physics and chemistry easily and freely - Science for elementary school, middle school and high school

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


Mixtures and solutions


1) Usefulness of chromatography

Chromatography is used to separate different colored substances in a mixture in order  to determine its composition.

2) Chromatography of a mint syrup: preparation

We first need to prepare the chromatography paper:
- The chromatography paper can be simply realized with a retangle of filter paper.
- A line must be drawn at about 1 cm from the bottom (using a pencil because ink can contain dyes that could disrupt chromatography): it is the origin line.
- A drop of mint syrup is deposited with a pipette on the origin line.

Chromatography paper

We then prepare the chromatography tank:
- This can be a simple beaker.
- Some water is poured ( about one centimeter ).

chromatography tank

3) Realization of chromatography

The chromatography paper must be suspended in the tank and must soak in water without wetting the origin line.
Through capillary action, the water is sucked through the filter paper and rises (such as coffee that rises in a sugar).

The rising water brings with it the drop of mint syrup from which are separated a yellow dye and a blue dye.

chromatography of mint syrup

This experiment shows that the green dye from mint syrup is actually a mixture of two colors: a yellow dye and blue dye.

4) Principle of chromatography

The water that rises in the chromatography paper brings with it a blue and a yellow dyes, but yellow dye moves slowlier than blue, they therefore separate and form two distinct spots.

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


©2021 Physics and chemistry