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Lecture10

# Lecture10 - -5 1 Buffer pH 2 pH after adding 0.10 mol of...

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Common Ion Effect, Buffered Solutions Reading: 15.1 to 15.3 HW: P736 # 9, 11, 15, 17, 21, 23, 27, 31, 35, 37, 39, 45

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Common Ion Effect Have 200 mL 1.0 M HF(aq) (K a = 7.2 x 10 -4 ) 1) [H 3 O + ] 2) pH Add 0.20 mol of KF(s) to solution. 1) [H 3 O + ] 2) pH
Common Ion Effect Have 200 mL 1.0 M NH 3 (aq) (K b = 1.8 x 10 -5 ) 1) [OH - ] 2) pH Add 0.10 mol of NH 4 Cl(s) to solution. 1) [OH - ] 2) pH

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Buffers Solutions that are resistant to pH changes (consume both H + and OH - ) Weak conjugate pair in solution HF / F - NH 4 + / NH 3
Buffer Action Buffer 1: HF / F - Buffer 2: NH 4 + / NH 3 1) Reaction when H + is added? 1) Reaction when OH - is added?

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Water vs. Buffer
Buffer Capacity

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Buffer pH Method 1: Ionization Constant K a = [A - ][H + ] / [HA] , pH = -log [H + ] Method 2: Henderson-Hasselbach equation pH = pK a + log ( [A - ] / [HA])

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1.0 L of buffer solution prepared with 0.75 M NaCH 3 COO(aq) and 0.75 M CH 3 COOH(aq) (Ka = 1.8 x 10

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Unformatted text preview: -5 ). 1) Buffer pH? 2) pH after adding 0.10 mol of HCl? • 0.50 L of buffer prepared with 0.50 M NH 3 (aq) and 0.50 M NH 4 Cl(aq). (K a of NH 4 + = 5.6 x 10-10 ) 1) Buffer pH? 2) pH after 0.10 mol HCl added? • Have 100 mL of 0.50 M H 2 CO 3 (aq), K a 7.2 x 10-7 . 1) What mass of NaHCO 3 (s) must be added to buffer at pH 6.5? • Assume both buffer are made up of same conjugate pair, HA and A-1) Why do both buffers have same original pH? 1) Why does is the pH change for buffers different after NaOH is added? Buffer 1 Buffer 2 Original pH 4.7 4.7 pH after 0.15 mol NaOH added 4.8 6.0 Buffered or Unbuffered? • Solution 1: 0.50 mol HCl, 0.50 mol NaOH • Solution 2: 0.50 mol HCl, 0.25 mol NaOH • Solution 3: 0.50 mol HOCl, 0.50 mol NaOH • Solution 4: 0.50 mol HOCl, 0.25 mol NaOH...
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