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Unformatted text preview: SPRING 2006 CHEM 110 EXAM 4 SHOW ALL WORK NO WORK, NO CREDIT 1. (15 pts) (a) Calculate the pH of a buffer which contains 0.20 M NH 3 and 0.25 M NH 4 Cl. (The K b of NH 3 is 1.8 x 10 5 ) pH = _________________ (b) What is the pH of the buffer after the addition of 5.0 g KOH to 1.000 L of the buffer in part (a) ? (Assume no volume change.) pH = _________________ (c) What mass of sodium formate (HCO 2 Na) must be added to a 250 mL solution of 0.150 M formic acid (HCO 2 H) to create a buffer with a pH of 4.00? (The pK a of formic acid is 3.745.) ___________________ g 1 SPRING 2006 CHEM 110 EXAM 4 SHOW ALL WORK NO WORK, NO CREDIT 2 (25 pts) Nicotinic acid, a B Vitamin, is a weak acid with K a = 1.4 x 10 5 . Suppose a 35.00 mL sample of 0.222 M nicotinic acid solution is titrated with a 0.100 M standard NaOH solution. (a) How many mL of NaOH would be required to neutralize all the acid? (i) 0.0158 (ii) 62.8 (iii) 0.0777 (iv) 15.8 (v) None of the above. Your answer is: _______________. (b) What would be the pH of a 35.00 mL sample of nicotinic acid (before titration)? (i) 0.65 (ii) 2.76 (iii) 1.00 (iv) 2.43 (v) None of the above. Your answer is: _______________. (c) What is the pH of the sample after the addition of 25.00 mL of 0.100 M NaOH?...
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