Basicity and Properties of Acids

Definition: Basicity of an acid is the number of replaceable hydrogen ions (H⁺) present in one molecule of the acid when it ionizes.  

Example:  

  - HCl → Monobasic (1 replaceable H⁺)  

  - H₂SO₄ → Dibasic (2 replaceable H⁺)  

  - H₃PO₄ → Tribasic (3 replaceable H⁺)  

Physical Properties of Acids  

1. Turn blue litmus paper red.  

2. Concentrated acids are corrosive.  

3. Dilute acids taste sour.  

4. Strong acids can destroy fabric and burn skin.  

5. Acids act as electrolytes, conducting electricity in solution.  

Chemical Properties of Acids  

1. Reaction with Metals

- Most acids react with metals to liberate hydrogen gas.  

- Exception: Trioxonitrate(V) acid (HNO₃) does not liberate hydrogen because it is a strong oxidizing agent; its hydrogen atom cannot be displaced by metals.  

2. Reaction with Bases (Neutralisation) 

- Acids react with bases/alkalis to form salt + water.  

- This reaction is called neutralisation.  

3. Reaction with Trioxocarbonates(IV)  

- Acids react with carbonates to form:  

  - Salt + water + carbon(IV) oxide (CO₂) gas.  

4. Reaction with Trioxosulphates(IV) 

- Acids react with sulphites to liberate sulphur(IV) oxide (SO₂) gas.