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Water - It's Composition and Reaction

 

From several experiments, water has been found to be composed of two elements - hydrogen and oxygen. If hydrogen is burn in oxygen, the only product obtained is water.

Two volumes of hydrogen and 1 volume of oxygen form two volumes of steam,

 i.e. 2H2(g) + O2(g) → H2O(g)

Or 1 volume of hydrogen and half volume of oxygen form 1 volume of water,

i.e. H2(g) + ½ O2(g) → H2O(g)

Hence, the formula of water is H2O

Test For Water

Water can be identified in the following ways:

(i). By it’s turning of white anhydrous copper(II) sulphate (CuSO4) to blue crystals,

i.e., CuSO4(s) + 5H2O(l) → CuSO4 . 5H2O(s) White blue

(ii). By its turning of blue anhydrous cobalt(II) chloride, CoCl2 to pink crystals, i.e. CoCl2(s) + 6H2O(s) → CoCl2 . 6H2O Blue pink

Water as A Solvent

Water can dissolve almost every substance on earth to some degree. For this reason, water is said to be a universal solvent. In the laboratory, water is used to dissolve particles of reacting masses, so that they are able to move freely and hence undergo reactions easily - water however will not react with them, it is only a medium.

Example, AgNO3(aq) + NaCl (aq) → AgCl(s) + NaNO3(aq)

lf the two reactants are solids, the reaction will not occur, therefore, they have to be in solution.

Atmospheric Gases Dissolved in Water and Their Biological Significance

Water, being able to dissolve most substances dissolves also certain atmospheric gases, such as oxygen, carbon(IV) oxide and nitrogen. Oxygen is slightly soluble in water. However, its presence in seas, rivers and other sources of water is very important to fish and other marine organisms which require oxygen for respiration. Carbon(IV) oxide is needed by plants for photosynthesis. Most aquatic organisms are unable to use atmospheric gases directly except when dissolved in water.

Reaction of Water with Metals

K
Na
Ca

React with cold water

Mg
Al
Zn
Fe

React with steam

Pb
Cu
Hg
Ag
Au

Do not react with water or steam

Related Tutorials

Soft and Hard Water
Removal of Hardness from Water
Purification of Town Water Supplies

  

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