Give an approximate pK_a value for each of the following acids using their  K_a values below:

1. Hydroiodic acid (HI), K_a = 3.2 × 10⁹

2. Ethanoic acid (CH ₃COOH), K_a = 1.8 × 10^-5

3. Oxalic acid (HO ₂C₂O₂H), K_a = 5.4 × 10^-2

4. Boric acid (H ₃BO₃), K_a = 5.8 × 10^-10

5. Carbonic acid (H ₂CO₃), K_a = 4.4 × 10^-7

6. Benzoic acid (C ₆H₅COOH), K_a = 6.3 × 10^-5

• A. 1. 8 to 9
  2. -4 to -5
  3. -1 to -2
  4. -9 to -10
  5. -6 to -7
  6. -4 to -5
• B. 1. -3.2
  2. -1.8
  3. -5.4
  4. -5.8
  5. -4.4
  6. -6.3
• C. 1. -10 to -9
  2. 4 to 5
  3. 1 to 2
  4. 9 to 10
  5. 6 to 7
  6. 4 to 5
• D. 1. -8 to -9
  2. 4 to 5
  3. 1 to 2
  4. -9 to -10
  5. -6 to -7
  6. 4 to 5

Answer: (C)