base and alkali

Base




 
Any such substance which gives hydroxyl ion (OH) when dissolves in water or give salt and water when treated with acid or neutralizes the acid is called base.
            KOH = K+ + OH
            NaOH = Na+ + OH
            Ba(OH)2 = Ba++ + 2OH
Combination of oxygen with metal results in the formation of metallic oxides. Metallic oxides are basic. E.g. copper oxide (CuO), sodium oxide (Na2O). Some metallic oxides are soluble in water and some are insoluble in water. Metallic oxides which dissolve in water produce corresponding hydroxide which is base. 
            Na2O + H2O = 2NaOH
A highly soluble hydroxide is an alkali. All alkalis are bases but all bases are not alkalis.

Some common alkalis are given below:

           
Name of Alkali
Molecular Formula
Potassium hydroxide
Sodium hydroxide
Calcium hydroxide
Ammonium hydroxide
KOH
NaOH
Ca(OH)2
NH4OH
Ammonium hydroxide gives strong smell of ammonia and it is injurious to health.




Characteristics of Base:

1. They produce hydroxyl ions when dissolved in water and the strength of base depends upon degree of ionization. A base which gives more hydroxyl ions is a strong base.
2. Strong bases posses a bitter taste and soapy touch.
3. They turn red litmus into blue, turmeric brown and phenolphthalein into pink.
4. Base reacts with acids to form salt.
2KOH + H2SO4 = K2SO4 + H2O

Preparation of Base:

            Bases can be prepared by following methods:
1. By the action of water on certain metals.
Ca + 2H2O = 2NaOH + H2
2. By the action of water on basic oxides.
Na2O + H2O = 2NaOH
3. By double decomposition.
 Na2CO3 + H2O = CaCO3 + 2NaOH




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