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Acid/Base Titration

Clinical Pharmacy Code: 105. Acid/Base Titration. Dr. Hisham Ezzat Abdellatef Prof. of Analytical Chemistry. 1. 2. 4. 3. Electrolyte and the theory of electrolytic Dissociation. Electrolytes conduct the electric current mineral acid, caustic alkalies and salts non – electrolytes

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Acid/Base Titration

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  1. Clinical Pharmacy Code: 105 Acid/Base Titration Dr. HishamEzzatAbdellatef Prof. of Analytical Chemistry

  2. 1 2 4 3

  3. Electrolyte and the theory of electrolytic Dissociation • Electrolytes • conduct the electric current • mineral acid, caustic alkalies and salts • non–electrolytes • non–conducting solutions • cane sugar, glycerin and ethyl acetate.

  4. Acid–Base Titration • Pure water is a bad conductor of electricity • acid as HCl H+ Cl- • base as KOH K+ OH- • salt as Na2SO4 Na+ SO42- • Molecule Dissociation ions Dissolved in water

  5. Strong and weak electrolytes • NaCl ⇌ Na+ + Cl– • K2SO4 ⇌ 2K+ + SO42– • Na2HPO4 ⇌ 2Na+ + H+ + PO43 • Arrhenius therefore introduced a quantity "a", called "the degree of dissociation“ • "a“ = 1 "strong electrolyte“ • “a” very far from unity.= weak electrolyte

  6. Law of mass action • "The rate of a chemical reaction is proportional to the active masses of the reacting substances." diluted solution concentration

  7. Law of mass action • Vf = [A].[B]. Kf • Vb = [C]. [D]. Kb • Kf [A]. [B] = Kb [C]. [D] "equilibrium constant"

  8. The dissociation of water • H2O ⇌ H+ +  OH– • [H+] . [OH] = Kw………..(2) • "The ionic product of water"

  9. The dissociation of water • 25oC; the value of Kw [H+] . [OH] = 1014 [H+]2 = Kw = 1 x 1014 ………(3)

  10. Hydrogen ion exponent (pH): [H+] 10–6, 10–51 x 10710–8 , 10–9 Acid base Neutral

  11. Procedure for Titration • pH is defined as equal to the logarithm of the hydrogen ion concentration with a negative sign. pH = –log [H+]

  12. The pH scale 1 2 3 4 5 678 9 10 11 12 13 14 acid neutral base Stomach juice: pH = 1.0 – 3.0 Human blood: pH = 7.3 – 7.5 Lemon juice: pH = 2.2 – 2.4 Seawater: pH = 7.8 – 8.3 Vinegar: pH = 2.4 – 3.4 Ammonia: pH = 10.5 – 11.5 Carbonated drinks: pH = 2.0 – 4.0 0.1M Na2CO3: pH = 11.7 Orange juice: pH = 3.0 – 4.0 1.0M NaOH: pH = 14.0

  13. Figure : The pH scale and pH values of some common substances

  14. Figure: A pH meter

  15. Figure: Indicator paper being used to measure the pH of a solution

  16. p pKw = pH + pOH  pH = pKw – pOH or pH = 14 – pOH or pOH = 14 – pH

  17. Acids and bases: • Arrhenius theory • Acid [H+] • when dissolved in water • Bases, [OH–]

  18. Acid and base

  19. pH calculations 1. Solution of strong acids and strong bases [H+] or [OH–] =concentration

  20. Example 1 • Calculate the pH value of a solution of a completely ionised 1.0 N solution of acid; or base. ? • Solution: [H+] = 1M pH = –log 1 = 0 (zero) similarly, in a completely ionised 1.0 N solution of base [OH–] = 1 M pOH = –log 1 = 0 (zero)

  21. Example 2 Calculate the [H+] and pH of 0.009 N hydrochloric acid? solution [H+] = 0.009 N pH =– log (9.0 X 10–3) = – log 9.0 – log 10–3 pH = – 0.95 + 3.00 = 2.05

  22. Example 3 • Calculate the pH values of a solution of sodium hydroxide whose [OH–] is 1.05 x 10–3? solution pOH = – (log 1.05 + log 10–3) pOH = – (0.02 –3 ) = 2.98 pH = 14 – 2.98 = 11.02

  23. Example 4 • Calculate the hydrogen ion concentration of a solution of pH 5.3? solution pH = – log [H+] 5.3 = –log [H+] [H+] = 5.01 x 10–6 M

  24. Example 5 • Calculate the hydroxyl ion concentration of a solution of pH 10.75 ? solution pOH = 14 – 10.75 = 3.25 [OH–] = the antilog of –3.25 [OH–] = 5.62 x 10–4 M

  25. pH calculations • 2. Solution of weak acids and bases • A) Calculation of pH of solution of weak acids pH = ½ (pKa + pCa)

  26. B) Calculation of pH of solution of weak bases: pH = pKw – ½ (pKb + pCb)

  27. pH of salts • A) Salts of strong acids or bases KCl K+ + Cl- K+ + OH- ⇌ KOH Cl- + H+ ⇌ HCl The equilibrium between the hydrogen and hydroxyl ions in water H2O ⇌ H+ +  OH–

  28. B) Salts of weak acids or bases (hydrolysis) • Salts of weak acids (or bases) react with water to give basic (or acidic) solutions • Hydrolysis reverse of neutralization

  29. i) Salts of weak acids and strong bases: H2O + CH3COO ⇌ CH3COOH + OH • pH = ½ (pKw – pCa + pKa)

  30. ii) Salts of weak bases and strong acids: NH4+ + H2O ⇌ NH4OH + H+ pH = ½ (pKw + pCs – pKb)

  31. acidic

  32. iii) Salts of weak acids and weak bases: pH = ½ pKw + ½ pKa – ½pKb

  33. Buffer solutions • Resist changes in pH caused by addition of small amounts of acid or base; or upon dilution.

  34. Types of buffers

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