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CHM2046Quiz4 - K a × K b = K w at 25 o C K b = K w/K a =...

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CHM2046 Quiz 4 Version A Answers underlined! 1a) What is the conjugate acid of HCO 3 ? add a proton, H + to HCO 3 A) H 3 O + B) H 2 O C) CO 3 2- D) OH E) H 2 CO 3 2a) Calculate the pH of a buffer that is 0.158 M HClO and 0.099 M NaClO. The K a for HClO is 8 2.9 10 × . A) 7.54 B) 6.67 C) 3.77 D) 6.46 E) 7.33 use ] [ ] [ log acid base pKa pH + = = -log 2.9 × 10 -8 ] 158 . 0 [ ] 099 . 0 [ log + pH = 7.538 -0.203 = 7.33 3a) Which of the following acids is the STRONGEST? The acid is followed by its K a value. The acid with the largest K a is the strongest. A) HF, 4 3.5 10 × B) HClO 2 , 2 1.1 10 × C ) HCN, 10 4.9 10 × D) HNO 2 , 4 4.6 10 × E) HCHO 2 , 4 1.8 10 × 4a) Determine the K b for CN at 25 o C. The K a for HCN is 10 4.9 10 × . K a
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Unformatted text preview: . K a × K b = K w at 25 o C; K b = K w /K a = 1.0 × 10-14 / 10 4.9 10 − × A) 14 4.9 10 − × B) 9 2.3 10 − × C ) 5 1.4 10 − × D) 5 2.0 10 − × E) 7 3.7 10 − × 5a) Determine the pH of a 0.227 M C 5 H 5 N solution. The K b of C 5 H 5 N is 9 1.7 10 − × . A) 4.59 B) 9.41 C) 4.71 D) 10.14 E) 9.29 C 5 H 5 N (aq) + H 2 O(liq) = HC 5 H 5 N + (aq) + OH-(aq) 0.227-x x x x x K b − = × = − 227 . 10 7 . 1 2 9 Omit x in denominator (x is v. small): x = [OH-] = √ (0.227)(1.7 × 10-9 ) = 1.96 × 10-5 pOH = -log (1.96 × 10-5 ) = 4.71 pH = 14 – 4.71 = 9.29...
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