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The usual error here is to just substitute the oh

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The usual error here is to just substitute the [OH - ] from the Ba(OH) 2 alone into the K w expression to find [H + ]; this gives an acidic pH value for the base Ba(OH) 2 . 023 3.3points One eq of HCl would neutralize exactly how many eq of KOH? 1. 3 2. 5 3. 4 4. 2 5. 1 correct Explanation: 024 3.3points How many grams of H 2 SO 4 are needed to make 455 mL of a 0.75 N solution? 1. 33400 g 2. 16.7 g correct 3. 33.4 g 4. 16700 g 5. 66.9 g 6. 0.375 g Explanation: V = 455 mL N = 0.75 N Normality equals molarity times the num- ber of equivalents per mole. H 2 SO 4 makes 2 equivalents of H + . N = M × 2 M = N 2 = 0 . 75 2 = 0 . 375 M H 2 SO 4 ? g H 2 SO 4 = 0 . 455 L H 2 SO 4 × 0 . 375 mol H 2 SO 4 L soln × 98 g H 2 SO 4 mol = 16 . 7 g 025 3.3points Solution A contains HCl and has a H + con- centration of 10 - 6 M. Solution B contains CH 3 COOH and has an H + concentration of 10 - 5 M. Which solution is more acidic and which solution has a greater pH? 1. Solution B is more acidic, but Solution A has a greater pH. correct 2. Both solutions have identical acidities and pH. 3. Solution A is more acidic and has a greater pH. 4. Solution A is more acidic, but Solution B has a greater pH.

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casey (rmc2555) – Homework 8 – holcombe – (51395) 8 5. Solution B is more acidic and has a greater pH. Explanation: [H + ] A = 10 - 6 M [H + ] B = 10 - 5 M pH = - log[H + ] The solutions have different concentrations of H + . Therefore, they will have different acidities and pH. The higher the H + concen- tration, the more acidic, and the lower the pH. 026 3.3points 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. H 3 O + 3. OH - 4. HA 2 - 5. A 3 - correct Explanation: 027 3.3points Consider the fractional composition dia- gram for the amino acid alanine. 0.2 0.4 0.6 0.8 1.0 2 4 6 8 10 12 14 pH Fractional Composition At pH = 3, what is the dominant species and what is its fractional composition? 1. - OOC CH(CH 3 )NH + 3 , 0.8 correct 2. - OOC CH(CH 3 )NH + 3 , 0.2 3. - OOC CH(CH 3 )NH 2 , 0.8 4. HOOC CH(CH 3 )NH + 3 , 0.8 5. HOOC CH(CH 3 )NH + 3 , 0.2 6. - OOC CH(CH 3 )NH 2 , 0.2 Explanation: To the left of 2 . 348, the red graph represent- ing HOOC CH(CH 3 )NH + 3 is dominant. Between 2 . 348 and 9 . 867, the blue graph representing - OOC CH(CH 3 )NH + 3 is dominant. To the right of 9 . 867, the green graph repre- senting - OOC CH(CH 3 )NH 2 is dominant. 028 3.3points Consider the polyprotic acid H 3 AsO 4 (arsenic acid), which has K a values, in no particu- lar order, of 10 - 7 , 10 - 2 , and 10 - 12 for the equilibria shown below: K a1 : H 3 AsO 4 ←→ H 2 AsO 4 - + H + K a2 : H 2 AsO 4 - ←→ HAsO 4 2 - + H + K a3 : HAsO 4 2 - ←→ AsO 4 3 - + H + Correctly identify the values of K a2 and K a3 1. K a2 = 10 - 7 , K a3 = 10 - 12 correct 2. K a2 = 10 - 2 , K a3 = 10 - 12 3. K a2 = 10 - 12 , K a3 = 10 - 2 4. K a2 = 10 - 7 , K a3 = 10 - 2 5. K a2 = 10 - 12 , K a3 = 10 - 7 6. K a2 = 10 - 2 , K a3 = 10 - 7 Explanation: Typically for polyprotic acids, each succes- sive deprotonation event is less spontaneous than the preceding event, and so has a smaller
casey (rmc2555) – Homework 8 – holcombe – (51395) 9 K a associated with it.
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