Pharmaceutical Aids and Necessities Quiz

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Pharmaceutical Aids and Necessities

• Topic Outline

  • Acids and Bases
  • Buffers
  • Waters
  • Antioxidants

• Objectives

  • Recall fundamental concepts of acids, bases, buffers, different types of pharmaceutical waters, and antioxidants, and their roles in pharmaceutical formulations.
  • Calculate pH, pKa, and buffer capacity.

• Introduction

  • Pharmaceutical aids and necessities are essential substances in the preparation, preservation, and storage of pharmaceutical products.
  • These are typically categorized into official inorganic acids, bases, buffers, antioxidants, various types of water, and glass materials.

• Acids

  • Sour in taste
  • Turn blue litmus red
  • Change methyl orange to red
  • Phenolphthalein remains colorless
  • Do not give soapy touch
  • Give hydrogen ions in solution

• Bases

  • Bitter in taste
  • Turn red litmus blue
  • Change methyl orange to yellow
  • Phenolphthalein gives pink colour
  • Soapy to touch
  • Give hydroxyl ions in solution

• Acid-Base Theories

  • Arrhenius: Produce H+ ions in water / Produce OH- ions in water
  • Brønsted-Lowry: Proton donor / Proton acceptor
  • Lewis: Electron acceptor / Electron donor

• Arrhenius Concept

  • Limited to aqueous systems
  • Acids form H+ ions in water
  • Bases form OH- ions in water (examples: HCl, NaOH)

• Examples of Arrhenius acids and bases (table format)

  • Arrhenius Acids | Arrhenius Bases
  • HClO3 | NaOH
  • HNO3 | NH4OH
  • HClO4 | KOH
  • H3PO4 | Mg(OH)2
  • H2SO4 | Ca(OH)2
  • H2SO3 | Al(OH)3
  • HCl | CH3COOH
  • CH3COOH
  • HBr

• Examples (solutions in water)

  • NaOH (aq) --> Na+ (aq) + OH-(aq)
  • KOH (aq) --> K+ (aq) + OH-(aq)
  • Ca(OH)2(aq) -->Ca2+ (aq) + 2OH (aq)
  • Mg(OH)2 (aq) --> Mg2+(aq) + 2OH-(aq)
  • NH4OH (aq) --> NH4+ (aq)+ OH-(aq)

• Brønsted-Lowry Concept -Acid = proton donor (H+) -Base = proton acceptor

• Conjugate Acid-Base Pairs

• Conjugate acid forms when a base accepts a proton.

• Conjugate base forms when an acid donates a proton.

• If an acid is strong, the conjugate base is weak

• If a base is strong, the conjugate acid is weak.

• Dissociation Constants for Acids and pH

  • Brønsted acid strength is reflected by the degree of dissociation of the proton from the conjugate base when acid is dissolved in water (HA + H2O = H3O+ + A-)
  • Degree of dissociation (ionization) is expressed via the equilibrium constant (Keq)
  • Ka (acid ionization constant) = Keq [H2O] = [H3O+] [A-] / [HA]
  • Ka varies directly with the strength of the acid (strong acids — HCl, H2SO4, HNO3 — have large ionization consonants (Ka > 1)).

• Strength of an acid

  • Expressed by the hydrogen ion concentration ([H+])
  • In aqueous solutions, [H+] is usually equal to [H3O+].
  • Kw (ion product constant of water) = [H3O+][OH-] = 1 x 10-14 at 25°C
  • [H3O+] = [OH-] = 1 x 10-7 in pure water
  • pH = -log[H+] = -log[H3O+]
  • ↑ concentration of hydrogen ion = ↑ acidity = ↓ pH

• Henderson-Hasselbalch Equation to calculate Ka and pH related values

• Dissociation Constants for bases and pOH: B + H2O = BH+ + OH- Keq = [BH+][OH-] / [B] [H2O]; Kb = Keq [H2O] = [BH+] [OH-] / [B]; pH = 14 – pOH

• Relationships between Ka, Kb ,pH, pOH, and pKw: Ka x Kb = Kw = 1 x 10-14; pKa + pKb = pKw = 14; pKw = pH + pOH = 14

• Percent Ionization

  • Important in understanding absorption, distribution, and excretion of drugs.
  • Used to understand drug behavior in the body. Most drugs are weak acids/bases (weak electrolytes)
  • Ionized molecules do not readily cross biological membranes.

Specific Inorganic Acids, Bases, and Water-related Information (e.g., boric acid, hydrochloric acid) is not included here, as it would take up too much space. Individual compounds are covered separately.

Additional Topics

• Buffers (Henderson-Hasselbalch), pH calculation examples
• Specific inorganic substances, properties, preparation, uses, and tests for identity. (separate entries)
• Official Waters (e.g., Water for Injection), properties, preparation, and purpose.
• Pharmaceutically Accepted Glass, types and characteristic properties