Calculate the pH of i) 0.300 M and ii) 0.030 M HNO₂ solution. In which case do you have to use the quadratic formula? The K_a of HNO₂ is 4.0 × 10^–4.

• A. i) pH = 2.26
  ii) pH = 1.92
  Case i) requires the quadratic formula.
• B. i) pH = 1.96
  ii) pH = 2.49
  Case ii) requires the quadratic formula.
• C. i) pH = 1.42
  ii) pH = 2.18
  Both i) and ii) requires the quadratic formula.
• D. i) pH = 2.31
  ii) pH = 1.19
  Neither requires the quadratic formula.

Answer: (B)