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


Acidic and basic solutions

Dilution of acids and bases

1) What is a dilution ?

Dilution simply consists in adding water in an aqueous solution.
It makes increase the proportion of solvent compared to that of the solutes.

2) Precautions for diluting

When a solution of acid or base is mixed with water some precautions must be taken:
- Protective gloves should be worn.

- It is better to add the acid solution in water and not the opposite because the water in contact with a large amount of acid can cause temperature rises more or less violent which projects some acid droplets.
This precaution especially concerns highly acidic solutions



3) Effects of dilution on pH

If we dilute an acidic solution:
- The solution becomes less acidic.
- Its pH increases and approaches 7.

If we dilute a basic solution:
- The solution becomes less basic.
- Its pH decreases and approaches 7

Comment: The dilution of an acidic solution increases its pH but it can not become greater than 7 because the added water is not basic.
Conversely the dilution of a basic solution decreases its pH, but it can not be less than 7 because the added water is not acidic