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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

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



Tests for ions

The presence of certain ions in an aqueous solution can be detected by making chemical tests.

1) Tests for ions with a precipitation reaction

The presence of certain ions in an aqueous solution can be detected by making chemical tests.
A test for ions is performed in several steps:
- A small part of the tested solution is taken and placed in a test tube.
- A few drops of a chemical called "reactive" are added in this test tube. The reactive is supposed to react with tested ions.

- The result is observed: if the searched ion is present in the solution then a chemical transformation takes place and produces a solid compound which looks a bit like gelatin and that is called "precipitate". Its color must be checked and compared to the expected color.


Example:test for copper ions.

Step 1: some solution is poured in a test tube
Test for ion: copper ion

Step 2: A few drops of an aqueous solution of sodium hydroxide (which acts as a reactive) are added
test for ions: copper ion

Step 3: A blue precipitate forms which confirms the presence of copper ions
Test for ions - precipitation reaction

To realize a test, we must therefore know the reagent to be used and the color of the precipitate that should form.

2) Some tests to know

Ion Iron (II) ion Fe2+ Iron (III) ion Fe3+ Copper ion Cu2+ Chloride ion Cl-
Reactive Sodium hydroxide Sodium hydroxide Sodium hydroxide Silver nitrate
Color of the precipitate Green Red Blue White
(Blackens in the light)