Pharmaceutical inorganic chemistry-1st || Acid and base

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      ✯Acid and base✯

Acid -

Greek word "Acere"  → Sour

★ It produced hydrogen ion in water.
★ Have a sour taste.
★ It breakdown metals , crod metal .
★ It is pH value less than 7 .
★ It turns blue litmus paper to red in colour.
★ It deserve in water to form solution which conduct electricity.
★ It is reaction with bases to for salts and water.
★ Lower pH value indicate a stronger acid .

Example — Hydrochloric acid, Sulphuric acid, acetic acid, citric acid etc.

Bases-;

★ It produces OH¯ in water.
★ It is bitter in taste.
★ It feel soapy in touch, sleepery.
★ It react with acids to for salt and water.
★ It pH value is 7 to 14.
★ Hayer pH value indicate stronger base.
★ Alkali a base that is soluble in water.

Example- NaOH  , KOH , MgOH , Ca(OH)₂

Acid-base indicator-;
Acid base indicator in a compound that will change colour in the presion of acids and bases 

Litmus paper— Litmus is a plant extract that can be blue or red ( pink) .
Litmus turns red in acidic solution and litmus turns blue to basic Solution.

Acid - base theory-;

1. Aorhenius theory 
2. Bronsted- Lowery theory
3. Lewis 'theory

 1. Aorhenius theory— The most commonly used concept acids bases was develop by savante Aorhenius in 1884.

Term as Aorhenius theory-;
According to this theory an acid is a substance which desociate in a aqueous solution and produce hydrogen ion Hᐩ on the other hand a base is a substance which desociate in aqua solution to produce hydroxy ion OH¯ .

Example- HCl ia an Aorhenius acid and NaOH is an Aorhenius base.

HCl      →     Hᐩ      +     Cl¯

Limitations-;
(1. ) Acids and base have been defined only in terms of solution and not as a solid substance.

(2.) This theory failed in elaborating the acidic and basic property of as substance in non - aqueous solvent.
Example- NH₄NO₃ does not give Hᐩ but act as an acid in liquid NH₄.

(3.) This theory also failed to explain the neutrolyzation of acids and base in the absense the solvent.

(4. ) There are mainy basic substances few organic substances an NH₃ ( which do not have OH¯ but have basic in nature . This fact could not be explain by Aorhenius theory.

(5.) Acetic properties in many salt (AlCl₃) in aqua solution could not be explain by this theory.

Bronsted  and Lowery Theory-;

In 1923 J.N. bronsted and J.N. Lowery independently introduce a broader concept of acid and base according to this theory an acid is any molecules or ion that can donate a proton [Hᐩ]  and base is any molecules or ion that can be accept or proton .

A base qualifying is termed as bronsted- Lowery base or bronsted base were as an acid qualifying bronsted - Lowery concept it term as bronsted Lowery acid or bronsted acid.


HA      →    Hᐩ     +    A¯

The pair of substances thus related throw mutual ability to gain or loss a proton is called conjugate acid base pair.

Example-        HCl    ⇌     Hᐩ   +    Cl¯

In conjugate acid base pair , strong acid have its weak conjugate base and weak have strong conjugate base .

Example-    HCl   +  H₂O     ⇌  H₃Oᐩ     + 
           Bronsted acid                     conjugate  Conjugate                                                          acid.               Base      

Limitations-
(1.) This theory works for all protic solvent ( Acetic acid, water , liquid,amonia etc) Not only for water as Aorhenius theory but it does not explain the acid base behaviour in aprotic solvent such as Benzene, dixane, cyclohexane.

(2.) Bronsted Lowery theory close not describe the acid and basic nature of organic compound or bronsted Lowery theory a acids and bases is passed on Transfer of proton commonly more acid and basic protonic nature  but some or not.

Example- BCl ,AlCl₃ do not have any hydrogen and hence can not give a proton but are known to behave as acid.

Lewis 'theory-;

★ A more genual modal of acids and bases was given by G.N.lewis in 1930.
In Lewis theory of acid base reaction bases donate pair or electron and acids accept pair of electron according to this concept.

1. Lewis acid are cation or more molecule heavy a loan pair of electron.

2. Lewis acids are cation or more molecule less on an electron pair.

                Acid                                    Neutral
 Agᐩ, Clᐩ                                    SnCl₄ , AgCl₃

   Base                            Lone pair donor
Cl , Br                                    NH₃


Advantage-; 
1. The Lewis concept explain the acidic and basic nature on the basis of transfer or gain of electron accompanied by loss or donosion of electron pair.

2. It includes the diffination given by both Aorhenius by bronsted Lowery theory.

3. It overcom the disadvantage of bronsted Lowery theory O₂ could not incumpass within the difination of an acid.

Limitations-;
★ Lewis acid and bases can not be arrange in there order of strength as their strength depends by reaction types .

★ lewis acid and bases reaction are expected to be very pass due to the environment of electron put some of these reactions are showed.



Thankyou ,







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