Más contenido relacionado


acid base theory for Bpharm 1st year students

  1. ACID AND BASE Venkata Kumar Sahu Pharmaceutical Analysis
  2. OBJECTIVE: • 1. To Understand the Definitions of Acid and Base • 2. To learn theories of acid and base
  3. Common Lab acids
  4. Common Lab Bases
  5. Every day example of Neutralization Indigestion remedies are bases that neutralise excess stomach acid Toothpaste is a base that neutralises acid in the mouth
  6. Lewis Theory A Lewis acid is an electrophilic species that accepts a pair of electrons from ions or molecules. A Lewis base is a nucleophilic species that donates a pair of electrons to ions and molecules. Lewis acid and base can react with one another by transferring electrons to form a covalent bond resulting in a simple or complex molecular structure. The product formed by a Lewis acid-base reaction is known as adduct
  7. Mechanism
  8. Lewis Acid and Base
  9. Examples of Lewis Acid and Base Lewis acid can be • Any cation that can accept electron pair: H+, Mg2+, Fe3+, NH4 +, and H3O+ • Any molecule with an incomplete octet of electrons: BF3 and AlCl3 • Any molecule where the central atom can have more than 8 electrons in its valence shell: SiCl4 and SiF4 • Any molecule that can have multiple bonds between two atoms of different electronegativity: CO2 and SO2 • Lewis base can be • Any simple anion that can give up a lone pair of electrons: O2-, Cl–, F–, and H– • Any anionic species containing a lone pair of electrons: OH–, CN–, CH3 –, and SO4 2- • Any molecule with an extra pair or pairs of electrons: H2O, NH3, and C(CH3)Cl • Any electron-rich pi system: benzene (C6H6), ethylene (C2H4), and ethyne (C2H2) •
  10. APPLICATION Applications of Lewis Acid • Friedel-Crafts alkylation reaction (method of generating alkylbenzenes by using alkyl halides as reactants) Applications of Lewis Base • Formation of ligands • Modification of metallic catalyst • Form bonds with Lewis acids to produce chelating agents
  11. THEORIES OF ACID AND BASE AND THEIR SCOPE Illustration of the hierarchy of acid-base theories. Arrhenius acids and bases are a sub-class of Brønsted acids and bases, which are themselves a subclass of Lewis acids
  12. USANOVICH THEORY Usanovich (1934) modified the Lewis concept of acid and base by removing the restriction of either donation or acceptance of the electron pair in a more generalized fashion. Acid : It is a chemical species that reacts with a base thereby giving up cations or accepting anions or electrons. Base : It is a chemical species that reacts with an acid thereby giving up anions or electrons or combines with cations Usanovich’s concept in a much broader sense includes all the oxidizing agents as acids and the reducing agents as bases, e.g.,
  13. LUX-FLOOD CONCEPT The concept of acid-base reactions with respect to the oxide ion was first introduced by Lux (1929) and supported by Flood (1947). According to the Lux-Flood concept—‘an acid is the oxide-ion acceptor while a base is the oxide donor’. Merit: This approach emphasizes the acid and basic-anhydride aspects. Acidic oxides are acid anhydride and in the aqueous medium generate protonic acids, while, basic oxides are basic anhydride and generate hydroxyl ions in the aqueous medium. Demerit: The usefulness of this concept is limited to species that contain oxide ion. The concept is applicable only in the molten state of an oxide.