ACIDS

ACIDS-

  • Acids are sour to taste. 
  • They change the color of methyl orange from orange to red, Phenolphthalein remains colorless in acidic solutions.
  • Aqueous solution of acid conduct electricity.

On the basis of origin, acids are classified as :

  • Organic acids: Acids derived from living organisms like plants and animals.

Natural sources of acids are:

Natural source

Acid

Natural source

Acid

Vinegar

Acetic acid

Sour milk (Curd)

Lactic acid

Orange

Citric acid

Lemon

Citric acid

Tamarind

Tartaric acid

Ant sting

Methanoic acid

Tomato

Oxalic acid

Nettle sting

Methanoic acid

 

  • Mineral acids: They are also called inorganic acids. They are dangerous Example sulphuric acid (H2SO4), hydrochloric acid (HCl) etc.


On the basis of their strength, acids are classified as :

Strong Acids

Weak acids

Acids that give rise to more H+ ions are said to be strong acids.

Acids that give less H+ ions are said to be weak acids.

 

Examples:

 

Example:

 

 

 On the basis of their concentration, acids are classified as :

  • Dilute acids: Have a low concentration of acids in aqueous solutions.
  • Concentrated acids: Have a high concentration of acids in aqueous solutions.

On the basis of number of hydrogen ion, acids can be classified as :

  • Monoprotic acid – Such type of acid produces one mole of H+ ions per mole of acid, e.g., HCl , HNO3
  • Diprotic acid – They can produce two moles of H+ ions per mole of acid, e.g., H2SO4.
  • Triprotic acid – They produce three moles of H+ ions per mole of acid, e.g., H3PO4.
  • Polyprotic – They can produce more than three H+ ions per mole of acid.

Chemical properties of acids:

  • Acids react with active metals to give hydrogen gas.

Zn + H2SO3 →ZnSO4 + H2

  • Acids react with metal carbonate and metal hydrogen carbonate to give carbon dioxide.

NaHCO3 +HCl → NaCl + H2O + CO2

  • Acids react with bases to give salt and water. This reaction is called as neutralization reaction.

NaOH + HCl → NaCl +H2O

  • Acids react with metals oxides to give salt and water.

CuO + H2SO4 → CuSO4 + H2O

Uses of acids-

  • Hydrochloric acid is used in digestion.
  • Nitric acid  is used in the purification of gold and silver and in the explosives (TNT, TNB, picric acid, etc)
  • Oxalic acid is used to remove rust spot.
  • Boric acid is a constituent of eyes wash.
  • Formic acid is present in red ants.
  • Uric acid is present in urine of mammals.
  • Sulphuric acid is used in lead storage battery and in the manufacture of fertilizers, drugs, alum, etc.
  • Acetic acid and citric acid – flavouring agent and food preservatives.
  • Tartaric acid – souring agents for pickles and it is a component of baking powder.

Addition of Acids or Bases to Water

  • The process of dissolving an acid, specially nitric acid or sulfuric acid or a base in water is a highly exothermic one.
  • As a rule: Always add acid to water and never the other way!
  • The acid must be added slowly to water with constant stirring. If one mixes the other way by adding water to a concentrated acid, the heat generated causes the mixture to splash out and cause burns.