Chapter : 4. Acid Bases & Salts
Preparation of Bases
Preparation of Bases :
Bases can be prepared by the following methods.
1. By the direct union of a metal with oxygen Some metals when heated in air or oxygen form the oxides of the metals.
These oxides when dissolves in water make the hydroxides of metals.
Na2O + H2O → 2NaOH
K2O + H2O → 2KOH
CaO + H2O → Ca(OH)2
2. By the action of water or steam on some active metals Some active metals like sodium and potassium react with cold water to form hydroxides with the evolution of hydrogen gas.
2Na + 2H2O → 2NaOH + H2 ↑
Magnesium reacts with steam to form magnesium oxide with the evolution of hydrogen gas.
On passing superheated steam over red-hot iron, ferrosoferric oxide is formed and hydrogen gas is evolved.
3. By heating carbonates of some metals When calcium carbonate is heated, calcium oxide and carbon dioxide are formed.
CaCO3 → CaO + CO2 ↑
Similarly, when zinc carbonate is heated, zinc oxide and carbon dioxide are formed
ZnCO3 → ZnO + CO2 ↑
4. By the action of an alkali on a salt solution For example, when an aqueous solution of sodium hydroxide is added to an aqueous solution of magnesium sulphate, magnesium hydroxide gets precipitated and sodium sulphate remains in the solution.
Bases can be prepared by the following methods.
1. By the direct union of a metal with oxygen Some metals when heated in air or oxygen form the oxides of the metals.
These oxides when dissolves in water make the hydroxides of metals.
Na2O + H2O → 2NaOH
K2O + H2O → 2KOH
CaO + H2O → Ca(OH)2
2. By the action of water or steam on some active metals Some active metals like sodium and potassium react with cold water to form hydroxides with the evolution of hydrogen gas.
2Na + 2H2O → 2NaOH + H2 ↑
Magnesium reacts with steam to form magnesium oxide with the evolution of hydrogen gas.
On passing superheated steam over red-hot iron, ferrosoferric oxide is formed and hydrogen gas is evolved.
3. By heating carbonates of some metals When calcium carbonate is heated, calcium oxide and carbon dioxide are formed.
CaCO3 → CaO + CO2 ↑
Similarly, when zinc carbonate is heated, zinc oxide and carbon dioxide are formed
ZnCO3 → ZnO + CO2 ↑
4. By the action of an alkali on a salt solution For example, when an aqueous solution of sodium hydroxide is added to an aqueous solution of magnesium sulphate, magnesium hydroxide gets precipitated and sodium sulphate remains in the solution.
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