Classification of Acids

Acids can be categorised based on different properties.

Based on Source

- Acids can be classified as Mineral or Natural Acids based on their origin.

1. Natural /Organic Acids   : These are the Acids present in nature in plant and animal material.In general , these are weak acids. A few examples of natural acids and their sources are: 
   
   

   Name of the Acid	Source
   Acetic Acid	Vinegar
   Ascorbic Acid	Guava, Amla
   Citric Acid	Lemon, Orange and other citrus fruits
   Lactic Acid	Sour milk, Curd
   Methanoic Acid	Ant sting, Nettle sting
   Oxalic Acid	Tomato
   Tartaric Acid	Tamarind

   
   
   
   

2. Mineral / Inorganic Acids: These acids are synthesized and man-made by a series of chemical reactions and procedures.These are usually strong acids and can damage and burn through organic substances such as human skin. Some mineral acids and their formulas are:

   
   

   Examples	Formula
   Hydrochloric acid	HCl
   Nitric acid	HNO 3
   phosphoric acid	H 3 PO 4
   Sulphuric acid	H 2 SO 4
   Boric acid	H 3 BO 3

Based on Concentration : 

Acid solutions can be Concentrated and Diluted based on the ratio of acid to water.

1. Concentrated Acids :
   These are the acids which have high concentration of acid and comparatively lesser amount of water. For example: Laboratory type Sulphuric Acid (H ₂ SO ₄ ) ( roughly 98 percent by weight) is a concentrated acid and so is the acid produced in our stomach. Acid ions per unit volume of the solution is large.
   
   
2. Dilute Acids : These are acid solutions which have a higher percentage of water as compared to the actual acid. These are usually considered weak acids. For example: A dilute solution of H ₂ SO ₄ .

Note - Mixing an acid with water leads to decrease in the concentration of Hydronium ions. Since the number of ions per unit volume is reduced ,the solution is called a diluted solution. This process of reducing ions per unit volume is called dilution.

Based on Ionising capability : 

Acids are classified as Strong and Weak Acids Based on how they ionise (split up into charged particles in water) .

Strong Acids

These are acids that give rise to more H ⁺ ions in water and get completely ionised. For Example : HCl and other mineral acids are strong acids.

HCl → H ⁺ + Cl ^–

Note : The single arrow in the above reaction shows that HCl is completely ionised. This means that every single molecule of HCl has broken up into H ⁺ and Cl ^-   ions.

Weak Acids

These acids only get partially ionized in water and produce less amount of H ⁺ ions. For Example: Acetic acid and other organic acids are usually weak Acids.

CH ₃ COOH ⇌ CH ₃ COO - + H ⁺

Note: The double arrow pointing towards both left and right show that CH ₃ COOH has not completely ionised. Which means there are still some molecules of acetic acid (CH ₃ COOH ) which have not split up into ions.