Chemistry

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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.

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

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.





Science class

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
Volumetric mass density

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
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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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