7th Class Science Acids, Bases and Salts / अम्ल, क्षार एवं लवण Acid, Bases and Salts

Acids, Bases and Salts

Synopsis

• Some of the food items that man takes are usually sour or bitter to taste.

• The sour taste is due to the presence of acids while the bitter taste is due to the presence of bases.

• The word acid comes from latin word "acere" which means sour.

• Properties of acids:

(i) Sour in taste                

(ii) Corrosive in nature        

(iii) Turns blue litmus to red

• Properties of bases:

(i) Bitter to taste             

(ii) Feels soapy on touching   

(iii) Turns red litmus to blue

• Salts - Salts are produced by the neutralisation of acids with bases. They are also produced when acids react with metals or metallic oxides, and when bases react with acidic oxides, Acids react with salts to usually produce other acids and salts. They react with carbonates to produce \[C{{O}_{2}},\]salt and water.

• Indicators are special type of substances used to test whether a substance is acidic or basic Turmeric, litmus, china rose petals (Gudhal), etc., are some of the naturally occurring indicators.

• The solutions which do not change the colour of either red or blue litmus are known as neutral solutions.

• The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat.

Acid + Base \[\to \]Salt + Water (Heat is evolved)

e.g., Hydrochloric acid (HC/) + Sodium hydroxide \[(NaOH)\to \]

Sodium chloride (NaCl) + Water \[({{H}_{2}}O)\]

• Neutralisation in everyday life takes place in

(i) treating indigestion      

(ii) treating ant bite

(iii) soil treatment         

(iv) treating factory wastes