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# 027 32points which of acid x hx 10 3 m k a 1 32 10 6

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027 3.2points Which of Acid X [HX] = 10 3 M K a = 1 . 32 × 10 6 Acid Y [HY] = 10 3 M K a = 3 . 47 × 10 3 is the stronger acid? 1. They have the same strength. 2. Acid X is stronger. 3. I would have to know if X or Y is a strong acid. 4. Acid Y is stronger. correct Explanation: Acid Y has a larger K a value and is there- fore stronger. 028 3.2points Consider the ionization constants hypochlorous acid (HOCl) : K a = 3 . 5 × 10 8 ; ammonia (NH 3 ) : K b = 1 . 8 × 10 5 . A solution of ammonium hypochlorite (NH 4 OCl) is 1. neutral, because the cation and the anion hydrolyze to the same extent. 2. neutral, because the anion hydrolyzes to a greater extent than the cation. 3. basic, because the cation and the anion hydrolyze to the same extent. 4. acidic, because the anion hydrolyzes to a greater extent than the cation. 5. neutral, because the cation hydrolyzes to a greater extent than the anion. 6. neutral, because NH 4 OCl is a weak base/weak acid salt. 7. acidic, because the cation and the anion hydrolyze to the same extent. 8. acidic, because the cation hydrolyzes to a greater extent than the anion. 9. basic, because the cation hydrolyzes to a greater extent than the anion. 10. basic, because the anion hydrolyzes to a greater extent than the cation. correct Explanation: Compare NH + 4 + H 2 O NH 3 + H 3 O +

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Version 221 – Exam 3 – holcombe – (51395) 9 K a = 1 K b = 1 1 . 8 × 10 5 = 55555 . 6 OCl + H 2 O HOCl + OH K b = 1 K a = 1 3 . 5 × 10 8 = 2 . 85714 × 10 7 The production of OH occurs to the greater extent, making the solution basic. 029 3.2points A solution at a pH of 5.9 contains the weak acid HA and its conjugate base A . What percent of the acid is dissociated? ( K a = 10 6 and [HA] + [A ] = 10 3 M). 1. Not enough information is given. 2. between 90% and 100% 3. between 10% and 90% correct 4. < 10% 5. 100% Explanation: 030 3.2points Which of the following combinations CAN- NOT produce a buffer solution? All compo- nents are present in 0.10 M concentration. 1. KF and HF 2. HBr and NaBr correct 3. HNO 2 and NaNO 2 4. NH 3 and (NH 4 ) 2 SO 4 5. HClO and NaClO Explanation: All are weak conjugate acid/base pairs ex- cept for HBr / Br which is a strong conjugate acid/base pair. 031 3.2points Relative to water upstream, the pH of water increases as it passes over a newly constructed concrete dam. In central Texas, the water will have a carbonate-bicarbonate equilibrium system. HCO 3 (aq) H + (aq) + CO 2 3 (aq) K a = [H + ][CO 2 3 ] [HCO 3 ] What can you say about the water down- stream of the dam? 1. [CO 2 3 ] increases. correct 2. Two of these are correct. 3. [OH ] remains constant. 4. The value of K a increases. 5. [H + ] increases. Explanation: Raising pH lowers [H + ], which drives the equilibrium to the right, thus increasing the concentration of CO 2 3 . 032 3.2points Steve went into the lab and diluted 24 mL of 0.12 M Ba(OH) 2 to 1500 mL. It was Steve’s birthday ( 21 st ) and the temperature was a comfy 77 F. What is the pH of the solution Steve mixed up?
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