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General Awareness play a vital role in all  Examination. we can expect  Questions from different Topics.Here we have given Study Notes on ” Acid “ for SSC CGL Examinations 2019-20. Candidates those who are all preparing for the Examination can use this study material.



The term acid comes from Latin term ‘accre’ which means sour. It was first used in the seventeenth century by Robert Boyle to label substances as acids.

An acid is a substance which furnishes hydrogen ions (H+) when dissolved in water.

For example, in its aqueous solution hydrochloric HCl (aq) dissociates as:

HCl (aq) ⎯⎯→ H+(aq) + Cl–(aq)

Examples of acids

Some examples of acids are:

(i) Hydrochloric acid (HCl) in gastric juice

(ii) Carbonic acid (H2CO3) in soft drinks

(iii) Ascorbic acid (vitamin C) in lemon and many fruits

(iv) Citric acid in oranges and lemons

(v) Acetic acid in vinegar

(vi) Tannic acid in tea

(vii) Nitric acid (HNO3) used in laboratories

(viii) Sulphuric acid (H2SO4) used in laboratories

Common Indicators of Acid

Common Indicators of acid are a follows :-

1.  An acid turns blue litmus red .
2.  Methyl orange indicator gives a red colour in an acidic solution .
3.  Phenolphthalein is colourless in an acidic solution .

 

Classification of Acid 

On the basis of the extent of dissociation occurring in their aqueous solutions, acids are classified as

  1. strong acid and

      2.  weak acids.

strong acid :- 

The acids which completely dissociate in water are called strong acids Nitric acid completely dissociates in water

HNO3(aq) ⎯→ H+(aq) + NO-(aq)

There are only seven strong acids:-

1. HCl Hydrochloric Acid
2. HBr Hydrobromic Acid
3. HI Hydroiodic Acid
4. HClO4 Perchloric Acid
5. HClO3 Chloric Acid
6. H2SO4 Sulphuric Acid
7. HNO3 Nitric Acid

 

weak acids :- 

The acids which dissociate partially in water are called weak acids. All organic acids like acetic acid and some inorganic acids are weak acids. Since their dissociation is only partial, it is depicted by double half arrows.

HF(aq) ⇔ H+(aq) + F–(aq)

The double arrows indicates here that :-

(i) the aqueous solution of hydrofluoric acid not only contains H+ (aq) and F–(aq) ions but also the undissociated acid HF(aq).

(ii) there is an equilibrium between the undissociated acid HF(aq) and the ions furnished by it, H+(aq) and F– (aq)

 

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