Acid base concepts

ARRHENIUS THEORY
Bronsted-Lowery Theory
Lewis theory

1. Mr. H.N.SINGH School of Pharmacy Sharda University Gr.Noida ACID –BASE CONCEPTS

2. ARRHENIUS THEORY for ACIDS and BASES Proposed in 1884 by Svante Arrhenius ACIDS : An acid is a substance that contains hydrogen and produces H + in aqueous Solution. HCl ( aq ) H + + Cl - BASES : A base is a solution that contains ,the OH group and produces Hydroxide ions OH - , in aqueous solution. Ca(OH)2 Ca+2 + 2 OH - Neutralization is defined as the combination of H + ions with OH - ions to form H 2 O molecules. H + ( aq ) + OH - ( aq ) H 2 O(l)

3. Proposed in 1923 by N. Bronsted and T.M.Lowry Acid – any substance donating a proton, H + Base – any substance accepting a proton. An acid-base reaction is the transfer of a proton from an acid to a base. The complete ionization of hydrogen chloride, HCl in water is an acid-base reaction. Step 1: HCl ( aq ) H + ( aq ) + Cl - ( aq ) ( Arrehnius ) Step 2: H + ( aq ) + H 2 O(l) H 3 O + Overall: HCl ( aq ) + H 2 O(l) H 3 O + ( aq ) + Cl - ( aq ) (LB) Bronsted -Lowery Theory of Acids and Bases

4. Overall: HCl ( aq ) + H 2 O(l) H 3 O + ( aq ) + Cl - ( aq ) (LB) acid conjugate acid base conjugate base Overall: NH 3 ( aq ) + H 2 O(l) NH 4 + ( aq ) + OH - ( aq ) (LB) base conjugate acid acid conjugate base Whether water can act as an acid or base depends on the other species present

5. Lewis theory Proposed by G. N. Lewis An acid is any species that can accept a share in an electron pair. A base is any species that can make available or donate a share in an electron pair. Lewis base - an electron pair donor Lewis acid - an electron pair acceptor Lewis acid + Lewis base  Adduct

6. Lewis Acids & Bases A Lewis acid and base can interact by sharing an electron pair.

7. Lewis Acids & Bases A Lewis acid and base can interact by sharing an electron pair. Formation of hydronium ion is an excellent example. +

8. Other good examples involve metal ions. Such bonds as the H 2 O ---> Co bond are often called COORDINATE COVALENT BONDS because both electrons are supplied by one of the atoms of the bond. Lewis Acids & Bases

9. SOME EXAMPLES OF LEWIS ACID AND BASE: 1. LEWIS ACID: H + , NH 4 + , Na - , K + , CN +2 , Al +3 etc. 2. LEWIS BASE: NH 3 , H 2 O, OH - , Cl - , CN - etc .