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Unit 18A Study Guide

# Unit 18A Study Guide - Unit 18 A Study Guide 1 What...

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Unit 18 A Study Guide 1. What combination of substances will give a buffered solution that has a pH of 5.05? (Assume each pair of substances is dissolved in 5.0 L of water.) ( K b for NH 3 = 1.8 × 10 –5 ; K b for C 5 H 5 N = 1.7 × 10 –9 ) A) 1.0 mole NH 3 and 1.5 mole NH 4 Cl B) 1.5 mole NH 3 and 1.0 mole NH 4 Cl C) 1.0 mole C 5 H 5 N and 1.5 mole C 5 H 5 NHCl D) 1.5 mole C 5 H 5 N and 1.0 mole C 5 H 5 NHCl E) none of these 2. You have solutions of 0.200 M HNO 2 and 0.200 M KNO 2 ( K a for HNO 2 = 4.00 × 10 –4 ). A buffer of pH 3.000 is needed. What volumes of HNO 2 and KNO 2 are required to make 1 liter of buffered solution? A) 500 mL of each B) 286 mL HNO 2 ; 714 mL KNO 2 C) 413 mL HNO 2 ; 587 mL KNO 2 D) 714 mL HNO 2 ; 286 mL KNO 2 E) 587 mL HNO 2 ; 413 mL KNO 2 3. 15.0 mL of 0.50 M HCl is added to a 100.-mL sample of 0.442 M HNO 2 (K a for HNO 2 = 4.0 × 10 -14 )). What is the equilibrium concentration of 2 NO - ions? 4. A solution contains 0.250 M HA (K a = 1.0 × 10 -6 ) and 0.45 M NaA. What is the pH after 0.23 mole of HCl is added to 1.00 L of this solution? 5. A weak acid, HF, is in solution with dissolved sodium fluoride, NaF. If HCl is added, which ion will react with the extra hydrogen ions from the HCl to keep the pH from changing? 6. Which of the following is true for a buffered solution? A) The solution resists change in its [H + ]. B) The solution will not change its pH very much even if a concentrated acid is added. C) The solution will not change its pH very much even if a strong base is added. D) Any H + ions will react with a conjugate base of a weak acid already in solution. E) all of these 7. The following question refers to the following system: A 1.0-liter solution contains 0.25 M HF and 0.77 M NaF (K a for HF is 7.2 × 10 -4 ). What is the pH of this solution? 8. The following question refers to the following system: A 1.0-liter solution contains 0.25 M HF and 0.49 M NaF (K a for HF is 7.2 × 10 -4 ). If one adds 0.30 liters of 0.020 M KOH to the solution, what will be the change in pH? 9. Calculate the [H + ] in a solution that is 0.14 M in NaF and 0.20 M in HF. (K a = 7.2 × 10 -4 ) 10. Which of the following will not produce a buffered solution? A) 100 mL of 0.1 M Na 2 CO 3 and 50 mL of 0.1 M HCl B) 100 mL of 0.1 M NaHCO 3 and 25 mL of 0.2 M HCl C) 100 mL of 0.1 M Na 2 CO 3 and 75 mL of 0.2 M HCl D) 50 mL of 0.2 M Na 2 CO 3 and 5 mL of 1.0 M HCl E) 100 mL of 0.1 M Na 2 CO 3 and 50 mL of 0.1 M NaOH

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