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Mixtures and solutions


1) What is decantation ?

It simply consists in waiting that, in a heterogeneous mixture, constituents separate one each other spontaneously.

2) Example: decantation of a mixture of water and soil

Decantation of water and soil

After shaking the mixture,  the soil particles are dispersed in water.
We then observe:
- A layer of soil forms slowly to the bottom: it consists of particles that fall as a result of their weight.
- The liquid gradually brightens. Less dense particles fall slower.
- After a sufficiently long time, the liquid becomes clear since all particles have fallen to the bottom of the beaker.

3) Advantages and drawbacks of decantation

Decantation is a simple separation to implement since it requires no special equipment but obtaining a complete separation and a totally clear liquid can takes a long time (sometimes several days) if the  particles mixed to water are thin and of low density.

- The separation of water and oil after shaking also corresponds to a decantation  (  the only difference being that the oil rises to the surface ).
- Decantation also occurs in nature when water is mixed with soil or sand.

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
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Changes of state: mass and volume
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Mixtures and solutions

Heterogeneous mixtures
Homogeneous mixtures
Vaporization of water
Dissolving a solid in water
Conservation of mass on dissolving
Miscibility in water

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Volume and its units
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Mass of a liter of water
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The electrical neutrality of the atom


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Most common metals
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Corrosion of metals
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Electrons and free electrons
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The conductivity of aqueous solutions
Aqueous solutions and ions
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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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