What is an Acid

An acid is a substance that, when dissolved in water, produces ions.H^+ as the only positive ion,e.g.
HCL -H+  + CL^-

This process is known as ionization. The characteristic properties of an acid in solution are due to the presence of these hydrogen ions. Acids are classified into organic and inorganic (mineral)acids. The organic acid occurs as natural products in plants and animal materials, while inorganic acids are prepared from inorganic matter. Some examples of organic acids are ethanoic acid from vinegar, tartaric acid from grapes, lactic acid from milk, citric acid from lime and lemon, amino acids from protein, a fatty acid from fats and oils, and ascorbic acid (vitamin c) from orange, while inorganic acids include hydrochloric acid, HCL,trioxonitrate (V) acid, HNO3, Tetraoxosulphate (VI) acid, H2SO4,trioxocarbonate(IV) acid, H2CO3, Tetraoxophosphate (V) acid, H3PO4.etc.
The strength of an acid is determined by the concentration of hydrogen ions in its solution. Strong acid ionizes completely in water to give hydrogen ions and onions. The concentration of hydrogen ions is very high in strong acid solutions.


Basicity of an acid
The basicity of an acid is the maximum number of hydronium ions which one molecule of the acid is capable of producing in an aqueous solution,i.e., the number of replaceable hydrogen ions, H+ in one molecule of the acid. The basicity of an acid is not necessarily the number of hydrogen atoms contained in one molecule of the acid. for example, ethanoic acid, CH3COOH has hydrogen atoms per molecule, but only one of these is replaceable by metal. Hence, ethanoic acid is monobasic.
CH3COOH- H+ + CH3COO^-
Dibasic and tribasic acids can exhibit variable basicity because they can donate their protons all at once or in stages.


Physical properties of acids

1. Dilute acids have a sour taste
2. Acid turns blue litmus red
3. The concentrated form of strong acids are corrosive
   
   
   

Chemical properties of acid

Reaction with metals: metals that are much more electropositive than hydrogen, react with dilute acids to liberate hydrogen gas. Dilute trinitrate (V) acid is an exception to this reaction because it is a strong oxidizing agent.
Zn + HCL - ZnCl2 + H2
Mg + H2SO4 - mgSO4 + H2
Lead, which is only slightly more electropositive than hydrogen does not liberate hydrogen gas with dilute acid, but we give a similar reaction with hot concentrated hydrochloric acid.



Reaction with base and alkalis: acid reacts with insoluble base and alkali to form salt and water only. The reaction is known as the neutralization reaction.


Uses of acid
Acid is used:

1. In the manufacture of fertilizers, dyes, detergents, explosives, paint, soaps, textile, drugs, plastic, and other chemicals
2. In dissolving metals or removing rust
3. In the production of salt, soft drinks, and baking powder
4. As food preservatives and mild antiseptic or germicide
5. In oil refinery
6. As an electrolyte in the lead-acid accumulator
7. As drying, dehydrating, and oxidizing agents

Preparation of acids

• By the reaction between an acid anhydride and water
• By a direct combination of constituent elements in the presence of a suitable catalyst
• By displacing a weaker or more volatile acid from its salt by a stronger or less volatile acid.

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