Strength of Acids and Bases


 
 
Concept Explanation
 

Strength of Acids and Bases

Strength of Acids

: As we know ,an acid is a substance which in aqueous solution  dissociates to produce hydrogen ions .

The strength of an acid depends on the concentration of hydrogen ions which dissociates in water. Greater the number of hydrogen ions dissociates greater is the strength of an acid. On this basis acids can be classified as:

Strong Acids :

It is an acid that dissociates completely or almost completely in water.For eg:

                       large HCl(aq)leftrightharpoons H^+(aq)+Cl^-(aq) 

              Hydrochloric acid            Hydrogen ion       Chloride ion

                    large H_2SO_4(aq)leftrightharpoons 2H^+(aq)+SO_4^2^-(aq)

                   Sulphuric acid                  Hydrogen ion         Sulphate ion     

Weak Acids:

It is an acid which dissociates negligibly or almost incompletely in water .For eg:

                   large HCOOH(aq)rightleftharpoons HCOO^-(aq)+H^+

                        Formic acid                     Formate ion                    Hydrogen ion

                  large CH_3COOH(aq)rightleftharpoons CH_3COO^-(aq)+H^+

                   Acetic acid                                       Acetate ion                    Hydrogen ion

Strength of Bases:

We know that base is a substance which in aqueous solution dissociates to produce hydroxyl ion. Greater is the concentration of hydroxyl ion in the solution , greater will be the strength of a base.On this basis we can classify bases as:

Strong Bases :

A base that dissociates completely or almost completely in water called as strong base.For eg:

                                               large NaOHrightleftharpoons Na^++OH^-

                                  sodium hydroxide      sodium ion    hydroxide ion

                                                   large KOH rightleftharpoons K^++ OH^-

                          potassium hydroxide       potassium ion    hydroxide ion

                                                          

Weak Bases:

A base that dissociates in water only partially or negligibly are known as weak bases. For eg:

                                         large NH_4OH(aq)rightleftharpoons NH_4^++ OH^-

                               Ammonium hydroxide      Ammonium ion     Hydroxide ion

To measure strength of an acid or base we use a number scale called as pH scale.

pH Scale:  

It is a scale used for measuring hydrogen ion concentration.. Here stands for potenz which means power in German.It has value from 0(very acidic) to 14(very basic). Higher the hydronium ion (H_3O^+ or hydrogen ion concentration lower is its pH .

pH >7 , Indicates that the given solution is basic. For eg: NaoH have pH value of 14

pH<7 , Indicates that the solution is acidic.For eg: lemon juice have a pH value of 2.2

pH=7 , indicates that the solution is neutral.For eg: pure water or blood have pH about 7.4 , so neutral in nature.

Sample Questions
(More Questions for each concept available in Login)
Question : 1

If pH >7 ,It indicates that the given solution is _________________________ in nature.

Right Option : B
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Explanation
Question : 2

A solution 'A' has pH value zero. The solution is ___________________

Right Option : B
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Question : 3

Which of the following are correct :

(a) An acid is a substance which in aqueous solution  dissociates to produce hydrogen ions .

(b) Strong acid is an acid that dissociates completely or almost completely in water.

(c) Weak acids is an acid which dissociates negligibly or almost incompletely in water .

Right Option : D
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Explanation
 
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