Acids, Bases and Salts

Sour and bitter tastes of food are due to acids and bases, respectively, present in them. Acids produce H+ ions when dissolved in water. They turn blue litmus to red. Bases are those chemical substances which are bitter in taste and soapy to touch. They produce OH– ions when dissolved in water. They turn red litmus to blue. The acids can be classified on the basis of their strength, origin, basicity and their concentration. Acids are sour in taste and corrosive. When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed. When a base reacts with a metal, along with the evolution of hydrogen gas a salt is formed which has a negative ion composed of the metal and oxygen. When an acid reacts with a metal carbonate or metal hydrogencarbonate, it gives the corresponding salt, carbon dioxide gas and water. Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively. Mixing concentrated acids or bases with water is a highly exothermic process. Acids, Bases and Salts Indicators Indicators help in identifying acidic or basic nature of a substance. Indicators can be natural or synthetic. Litmus, turmeric, petunia petals are natural indicators. Methyl orange and phenolphthalein are examples of synthetic indicators. Red onion can act as a visual as well as olfactory indicator. Universal indicator is a mixture of dyes that shows different colours at different strength of acid and base in a solution. The strength of an acid or base is measured on a scale of numbers called the pH scale (0-14) which gives the measure of hydrogen ion concentration in a solution. A neutral solution has a pH of exactly 7, while an acidic solution has a pH less than 7 and a basic solution a pH more than 7. Living beings carry out their metabolic activities within an optimal pH range. When the pH becomes lower than 5.5 tooth enamel gets corroded. Plants require definite pH range for their proper growth. Acids, Bases and Salts Salts Acids and bases neutralise each other to form corresponding salts and water. A salt is formed when hydrogen ion of an acid is replaced by a metal ion or ammonium ion. Salt can be classified as acidic salt and normal salt. Sodium chloride, sodium sulphate and sodium nitrate contain same positive ion that is sodium ion therefore, they belong to the same family of salts called ‘family of sodium salts’. Similarly sodium sulpahte, calcium sulphate and copper sulphate contain same negative ion that is sulphate ion therefore, they belong to the ‘family of sulphate salts’. Salts have various uses in everyday life and in industries. Common salt is chemically known sodium chloride. Crude sodium chloride is obtained by evaporation of seawater. Chemically caustic soda is sodium hydroxide. It is a white, translucent, deliquescent solid that dissolves in water to give a strong alkaline solution. The chemical name of washing soda is sodium carbonate decahydrate. It is prepared by heating baking soda. Sodium hydrogen carbonate is chemical name of baking soda. It is white crystalline solid. Calcium oxychloride is the chemical name of bleaching powder. It is prepared by passing chlorine gas over dry slaked lime. Chemically plaster of Paris is calcium sulphate hemihydrates. It is prepared by heating gypsum at 373 K.

To Access the full content, Please Purchase