Fahkreddine_HW4

# The following statements about the acid hx is true 1

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the following statements about the acid HX is true? 1. HX is a strong acid. 2. HX is a weak acid with a K a value of about 10 4 . 3. HX would probably be a good acid-base indicator. 4. HX is a weak acid with a K a value of about 10 8 . correct 5. HX is a weak acid with a K a value of about 10 10 . Explanation: 021 1.0 points Which of the following solutions has the low- est pH at 25 C? 1. 0.1 M ammonia

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tu (pyt67) – Homework 4 – Fakhreddine – (52425) 6 2. 0.1 M acetic acid 3. 0.5 M formic acid correct 4. 0.5 M aniline Explanation: 022 1.0 points A 0.00100 M solution of a weak acid HX is 10% ionized. Calculate K a for the acid. Correct answer: 1 . 11111 × 10 5 . Explanation: 023 1.0 points List the acids HCOOH, (CH 3 ) 3 NH + , N 2 H + 5 , HF in order of increasing strength, if Acid p K a Base p K b HCOOH 3 . 75 (CH 3 ) 3 N 4 . 19 HF 3 . 45 NH 2 NH 2 5 . 77 1. HF, HCOOH, N 2 H + 5 , (CH 3 ) 3 NH + 2. (CH 3 ) 3 NH + , N 2 H + 5 , HCOOH, HF cor- rect 3. (CH 3 ) 3 NH + , HCOOH, N 2 H + 5 , HF 4. N 2 H + 5 , (CH 3 ) 3 NH + , HCOOH, HF 5. HF, HCOOH, (CH 3 ) 3 NH + , N 2 H + 5 6. HCOOH, HF, (CH 3 ) 3 NH + , N 2 H + 5 7. HF, N 2 H + 5 , HCOOH, (CH 3 ) 3 NH + 8. None of these 9. N 2 H + 5 , (CH 3 ) 3 NH + , HF, HCOOH Explanation: The stronger the acid, the larger its K a value and the smaller its p K a value from p K a = - log K a . To find the p K a for the conjugate acid of a weak base, use p K a + p K b = 14. Thus we have (CH 3 ) 3 NH + (p K a = 14 . 0 - 4 . 19 = 9 . 71) (weakest) N 2 H + 5 (p K a = 14 . 0 - 5 . 77 = 8 . 23) HCOOH (p K a = 3 . 75) HF (p K a = 3 . 45) (strongest) 024 1.0 points A 7 . 2 × 10 3 M solution of acetic acid is 5.0% dissociated. In a 7 . 2 × 10 4 M solution, the percent dissociation would be 1. < 5%. 2. None of these 3. > 5%. correct 4. zero. 5. the same. Explanation: 025 1.0 points An aqueous solution of nitrous acid HNO 2 has a pH of 1.96. The ionization constant of this acid is 5.0 × 10 4 . How much nitrous acid was used to prepare one liter of this solution? (Approximate the full quadratic equation.) Correct answer: 11 . 3 grams. Explanation: 026 1.0 points For a solution labeled “0.10 M H 2 SO 4 (aq),” 1. the pH is less than 1.0. correct 2. the pH is greater than 1.0. 3. the pH equals 1.0. 4. [SO 2 4 ] = 0.10 M. 5. [HSO 4 ] is greater than 0.10 M. Explanation: 027 1.0 points
tu (pyt67) – Homework 4 – Fakhreddine – (52425) 7 Calculate [H + ] for a solution labeled “0.0500 M H 2 SO 3 (aq).” (p K a1 = 1 . 81, p K a2 = 6 . 91) 1. 0.021 M correct 2. 0.029 M 3. 0.015 M 4. 0.025 M 5. 0.050 M Explanation: 028 1.0 points Calculate the equilibrium concentration of sulfurous acid in a solution labeled “0.100 M H 2 SO 3 (aq).” (p K a1 = 1 . 81, p K a2 = 6 . 91) 1. 0.015 M 2. 0.100 M 3. 0.050 M 4. 0.068 M correct 5. 0.032 M Explanation: 029 1.0 points The pH of 0.010 M H 3 PO 4 (aq) is 2.24. Esti- mate the concentration of HPO 2 4 in the solu- tion. For H 3 PO 4 , the values of K a1 , K a2 , and K a3 are 7 . 6 × 10 3 , 6 . 2 × 10 8 , and 2 . 1 × 10 13 , respectively.
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• Fall '07
• Holcombe
• pH, Acids

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