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= 9.20

NH 4 + ( aq ) H + ( aq ) + NH 3 ( aq ). pH = 9.25 + log. [0.25]. [0.30]. [NH 3 ]. pH = p K a + log. [NH 4 + ]. [0.28]. [0.36]. NH 4 + ( aq ) + OH - ( aq ) H 2 O ( l ) + NH 3 ( aq ). pH = 9.25 + log.

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= 9.20

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  1. NH4+(aq) H+(aq) + NH3(aq) pH = 9.25 + log [0.25] [0.30] [NH3] pH = pKa + log [NH4+] [0.28] [0.36] NH4+(aq) + OH-(aq) H2O (l) + NH3(aq) pH = 9.25 + log Calculate the pH of the 0.30 M NH3/0.36 M NH4Cl buffer system. What is the pH after the addition of 20.0 mL of 0.050 M NaOH to 80.0 mL of the buffer solution? pKa= 9.25 = 9.17 final volume = 80.0 mL + 20.0 mL = 100 mL 0.01 0.24 start (M) 0.29 end (M) 0.28 0.0 0.25 = 9.20 16.3

  2. Chemistry In Action: Maintaining the pH of Blood 16.3

  3. Titrations In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. Equivalence point – the point at which the reaction is complete Indicator – substance that changes color at the endpoint (hopefully close to the equivalence point) Slowly add base to unknown acid UNTIL The indicator changes color (pink) 4.7

  4. NaOH (aq) + HCl (aq) H2O (l) + NaCl (aq) OH-(aq) + H+(aq) H2O (l) Strong Acid-Strong Base Titrations 100% ionization! No equilibrium 16.4

  5. CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + H2O (l) CH3COOH (aq) + OH-(aq) CH3COO-(aq) + H2O (l) CH3COO-(aq) + H2O (l) OH-(aq) + CH3COOH (aq) Weak Acid-Strong Base Titrations At equivalence point (pH > 7): 16.4

  6. HCl (aq) + NH3(aq) NH4Cl (aq) H+(aq) + NH3(aq) NH4Cl (aq) NH4+(aq) + H2O (l) NH3(aq) + H+(aq) Strong Acid-Weak Base Titrations At equivalence point (pH < 7): 16.4

  7. Acid-Base Indicators 16.5

  8. pH 16.5

  9. The titration curve of a strong acid with a strong base. 16.5

  10. Which indicator(s) would you use for a titration of HNO2 with KOH ? Weak acid titrated with strong base. At equivalence point, will have conjugate base of weak acid. At equivalence point, pH > 7 Use cresol red or phenolphthalein 16.5

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