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Properties of Bases

1. Bases have a bitter taste and are slippery to touch.

2. Strong bases such as caustic soda (NaOH) and caustic potash are corrosive in nature and can harm the skin. These bases are highly soluble in water and the dissolution process is exothermic.

3. Alkalies are good conductors of electricity.

4. Indicator Properties

Aqueous solutions of bases impart specific colours to the acid-base indicators.

  • They tum red litmus blue.
  • They impart pink colour to phenolphthalein.
  • They impart yellow colour to methyl orange.
  • They impart yellow colour to methyl red.

5. Reaction with Acids

Bases react with acids to form salt and water

Base + Acid àSalt + Water

KOH + HCl àKCl + H2O

2NaOH + H2O àNa2SO4 + H2O

The reaction is known as neutralization.

 

6. Reaction with Metals

Certain metals such as zinc, aluminium, tin and lead react with strong alkali solutions, on heating, and hydrogen gas is evolved.

7. Reaction with Non-metallic Oxides

Non-metallic oxides are generally acidic in nature. They react with bases to form salt and water.

Base + Non-metallic  àoxide Salt + Water

For example,

Ca(OH)2 + CO2 à CaCO3 + H2O

2KOH + CO2 à K2CO3 + H2O

2NaOH + SO2 àNaSO3 + H2O

Concentrated solution of caustic potash is used for absorbing carbon(IV) oxide gas.

8. Reaction with Metallic Oxides

Certain metal oxides can act as bases as well as acids.These are known as amphoteric oxides. For example, zinc oxide (ZnO), lead(II) oxide.(PbO), aluminium oxide (.Al2O3).

These oxides on reaction with hot alkali solutions form complex salts and dissolve.

In these reactions metal oxides are acting as acids.

Now, let us learn about the various concepts of acids and bases: