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pb set 15

# pb set 15 - point and(b the second stoichiometric point in...

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Problem Set #15 Acid-Base Indicators & Polyprotic Titrations 1. Which of the following indicators could you use for a titration of 0.20 M CH 3 COOH(aq) with 0.20 M NaOH(aq): (a) methyl orange, (b) litmus, (c) thymol blue, (d) phenolphthalein? Explain. [See table 11.3] K a CH 3 COOH = 1.8x10 -5 2. Suppose that 25.0 mL of 0.10 M CH 3 COOH(aq) is titrated with 0.10 M NaOH(Aq). pH of the 0.10 M CH 3 COOH(aq) solution = 2.87 pH after the addition of 10.0 mL of 0.10 M NaOH(aq) = 4.57 pH at halfway to the stoichiometric point = 4.74 pH at the stoichiometric point = 8.72 Suggest a suitable indicator for the titration. 3. What volume of 0.275 M KOH(aq) must be added to 75.0 mL of 0.137 M H 3 AsO 4 (aq) to reach (a) the first stoichiometric point; (b) the second stoichiometric point; (c) the third stoichiometric point ? pK a1 = 2.19; pK a2 = 6.94; pK a3 = 11.5 4. What volume of 0.010 M NaOH(aq) is required to reach (a) the first stoichiometric

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Unformatted text preview: point and (b) the second stoichiometric point in a titration of 25.00 mL of 0.010 M H 2 SO 3 (aq)? pK a1 = 1.81; pK a2 = 6.91 5. Estimate the pH of the solution that results when each of the following solutions is added to 50.0 mL of 0.275 M Na 2 HPO 4 (aq): (a) 50.0 mL of 0.275 M HCl(aq); (b) 75.0 mL of 0.275 M HCl(aq); (c) 25.0 mL of 0.275 M HCl(aq). pK a1 = 2.12; pK a2 = 7.21; pK a3 = 12.68 6. What volume of 0.020 M NaOH(aq) is required to reach (a) the first stoichiometric point and (b) the second stoichiometric point in a titration of 30.00 mL of 0.010 M H 3 PO 4 (aq)? 7. A sample of 0.100 M H 2 S(aq) of volume 20.0 mL was titrated with 0.300 M NaOH(aq). Identify the primary species in solution and the pH after the addition of the following volumes of NaOH solution: (a) 5.0 mL, (b) 13.4 mL. pK a1 = 6.89; pK a2 = 14.15...
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