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Science class

Chemistry

Electricity

Optics

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

Combustions
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
Metals

Most common metals

How to distinguish metals ?

Corrosion of metals

Electrical conductivity of solid materials

Electrons and free electrons

Electric current in metals
Ions
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



















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Water

Test for water

   

The essential about test for water


How to identify water in a substance ?


This question worth asking because a liquid doesn't necessarily contain water, and a solid substance may contains water wich is not observable with the naked eye.
A Test for water must be used identify water.
Different tests exist but the most commonly used requires anhydrous copper sulphate.

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Anhydrous copper sulphate



The test for water requires a chemical compound: Copper sulfate anhydrous.
This is a white powder.
Comment: The term anhydrous is formed of "an" (privative prefix) and "hydrous" meaning "water": "anhydrous" is therefore almost synonymous with dehydrated.
                                      Photo of anhydrous copper sulphate
Photo: anhydrous copper sulphate      
Copper sulphate formula

The complete name is copper II sulphate which indicates that it contains copper II ions ( whose formula is Cu2+ ) and Sulphate ions ( whose formula is SO42-).
Copper sulphate formula is therefore CuSO4.

Hydrated copper sulphate

Diagram: water and anhydrous sulfate
Addition of water on anhydrous copper sulfat


White anydrous copper sulphate that has been in contact with water becomes hydrated copper sulphate and turns blue.
A copper sulfate hydrate still contains some CuSO4 cristals but also five water molecules ( H2O )
Copper sulfate hydrate can therefore also be called copper sulphate pentahydrate ( the penta prefix means "five" ).
This change of color is exploited to test for water.
                               Blue hydrated copper sulphate
 Photo: blue hydrated copper sulphate and white anhydrous copper  sulphate
Chemical test for water with anhydrous copper sulphate

Diagram: test for water in a liquid
test for water in liquid


Diagram: test for water in a solid
test for water in solid substances
 

In each case if the copper sulphate turns blue it can be concluded that the substance contains water.

Some results obtained with the test for water
 
Substance Apple juice Lemonade Cola Washing up liquid
Result Positive Positive Positive Negative
Is there water in the substance ? Yes Yes Yes No

Substance Oil Vinegar Petroleum Milk
Result Negative Positive Negative Positive
Is there water in the substance ? No Yes No Yes

Substance Apple Potato Tomato Paper
Result Positive Positive Positive Negative
Is there water in the substance ? Yes Yes Yes No

Conclusion:
Most of the foods (liquid or solid) contain water but in different percentages:
Meat: about 60%
A potato: about 80%
An apple: 85%
A Potato: 93%
A salad: about 95%
A tomato: 98%

Note: fats (such as oil or butter) are exceptions because they do not contain water
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Learn more about test for water

- Investigating the action of heat on copper sulphate: method to obtain anhydrous copper sulphate with hydrated copper sulphate.

- Hydrating anhydrous copper sulphate: video showing drops of water cast upon anhydrous copper sulphate.




 


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