7_new - Homework#6 holcombe(51160 This print-out should...

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Homework #6 – holcombe – (51160) 1 This print-out should have 19 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Consider a solution that is 0.10 M in a weak triprotic acid which is represented by the gen- eral formula H 3 A with the following ionization constants: K 1 = 1.0 × 10 −3 , K 2 = 1.0 × 10 −8 , K 3 = 1.0 × 10 −12 . Which species is present in the lowest concentration in 0.10 M H 3 A solution? 1. H 3 A 2. A 3− correct 3. HA 2− 4. OH 5. H 3 O + Explanation: 002 10.0 points Which of the following would be equal to K A 3 for orthocarbonic acid, H 4 CO 4 ? 1. [H + ] 3 · [HCO 3 4 ] [H 4 CO 4 ] [H 2 CO 2− ] 2. 4 [H + ] · [HCO 3 4 ] [H 4 CO 4 ] 3. [H + ] 3 · [HCO 3 4 ] 4. [H + ] · [HCO 3 4 ] [H 2 CO 2 4 ] correct 5. [H + ] 3 · [HCO 3 4 ] [H 2 CO 2 4 ] Explanation: K A 3 for orthocarbonic acid, H 4 CO 4 , describes the 3 RD deprotonation event. H 2 CO 2 4 ↔ H + + HCO 3 4 003 10.0 points Determine the pH of a 0.4 M solution of NaHCO 3 . Assume H 2 CO 3 has a pK A 1 of 3.60 and a pK A 2 of 10.4. 1. not enough information 2. 5.4 3. 0.7 4. 2 5. 7 correct Explanation: For a solution composed of a single ampho-teric species (HCO 3 ), pH = 0.5(pK A 1 + pK A 2 ) = 0.5(3.6 + 10.4) = 7 004 10.0 points Adding NH 4 NO 2 to pure water would result in what kind of solution? K A for HNO 2 is 4.5 × 10 −4 and K B for NH 3 is 1.8 × 10 −5 . 1. basic 2. acidic correct 3. neutral Explanation: 005 10.0 points Carbonic acid (H 2 CO 3 ) is a diprotic acid with K A1 = 4.2×10 7 and K A2 = 4.8 × 10 −11 . The ion product for water is K W = 1.0 × 10

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7_new - Homework#6 holcombe(51160 This print-out should...

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