Bases

Oxides of metals are called base. They are soapy to touch.

OR

Those compounds which release hydroxyl ion (Anion) in their aqueous solution are called base.

For e.g.

NaOH→Na⁺ + OH^-

Ca(OH)₂→ Ca⁺⁺+ 2OH^-

Mg(OH)₂ → Mg⁺⁺ + 2OH^-

Alkali: Some metallic oxides (base) give their respective hydroxide when dissolved in water. Such water-soluble bases are called alkalis.

Types of base

On the basis of strength, bases are of two types:

• Strong base: Those bases which go under complete ionization in aqueous solution and give the high concentration of hydroxyl ions are called strong bases.
• Weak base: Those bases which go under partial ionization in aqueous solution and give low concentration of hydroxyl ions are called weak bases.

Similarly, on the basis of their origin, bases are of two types:

• Organic bases: Those bases which are derived from living source are called organic bases.
• Inorganic bases: Those bases which are obtained from minerals are called weak bases.

Properties of base

1. Bases are bitter in taste and soapy feeling when touched.
2. They turn red litmus into blue, colorless phenolphthalein into pink, methyl orange to light yellow.
3. Base reacts with acid to give salt and water. NaOH(base) + HCl(acid)→NaCl(salt) + H₂O(water)
4. Alkalis react with carbon dioxide to produce carbonate salt and water. 2NaOH + CO₂→Na₂CO₃ + H₂O
5. Alkalis react with ammonium salts on heating to produce ammonia gas. NH₄Cl + NaOH→NH₃+NaCl+ H₂O

Uses of base

• Caustic soda (NaOH) is used for the manufacture of soap, paper and rayon. It is also used in the refining of petroleum products.
• Ammonium hydroxide is used for making chemical fertilizers.
• Caustic potash is used in the manufacture of soft soaps.
• Quick lime is used for softening hard water. It is also used in the manufacture of cement.

  

  Fig: Formation of hard water