Chemical Properties of Pure Water:
(a) Pure water is a natural compound; it is neither acidic nor basic in nature, and hence it does not have any effect on litmus.
(b) Pure water is a bad conductor of electricity. However, acidified water is a good conductor of electricity; it is split up in to its constituent atoms- hydrogen and oxygen- on passage of an electric current.
(c) Action of water on metals-
(i) Metals like sodium (Na), potassium (K) and calcium (Ca) react with cold water to form the corresponding alkali and hydrogen gas is released. The reaction is vigorous and gives out a lot of heat. The reaction between sodium and cold water is written as follows-
2Na + 2H2O ——–> 2NaOH + H2
Due to the heat of the reaction, hydrogen has catches fire.
Reaction with potassium and calcium-
2K + 2H2O ——–> 2KOH + H2
Ca + 2H2O ——–> Ca(OH)2 + H2
Potassium reacts with cold water more vigorously than sodium. The metal calcium is less reactive with water than sodium. It is safe to add metal calcium to water.
(ii) Cold water does not react with metals like Mg, Zn and Fe. Steam reacts with these metals when they are heated to redness. The products formed are the corresponding metal oxides and hydrogen gas.
Mixed reactions are less vigorous.
The equations of reactions are as follows-
Mg + H2O (Steam) ——–> MgO + H2
Zn + H2O (Steam) ——–> ZnO + H2
2Fe (Red Hot Iron) + 2H2O (Steam) ——–> Fe2O2 (Ferric Oxide) + 2H2
Metals such as gold, platinum, silver, lead, mercury and copper do not react with water or steam.
(d) Action of water with metal oxides- Oxides of sodium, potassium and calcium are highly soluble in water, forming hydroxides of these metals called alkalis.
Na2O (Sodium Oxide) + H2O ———–> 2NaOH (Sodium Hydroxide)
K2O (Potassium Oxide) + H2O ———–> 2KOH (Potassium Hydroxide)
CaO (Calcium Oxide) + H2O ———–> Ca(OH)2 (Calcium hydroxide)
(e) Action of water with non-metallic oxides- Oxides of non-metals such as carbon, nitrogen, sulfur and phosphorous are soluble in water giving their corresponding acids.
CO2 + H2O ———–> H2CO3 (Carbonic Acid)
SO2 (Sulfur Dioxide) + H2O ———–> H2SO3 (Sulfurous Acid)
SO3 + H2O ———–> H2SO4 (Sulfuric Acid)
P2O5 (Phosphorus Pentoxide) + 3H2O ———–> 2H3PO4 (Phosphoric Acid)
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