Practice: The K_{b} of C_{6}H_{5}NH_{2} (aniline) is 3.9 × 10^{−}^{10}. Determine pH of a buffer solution made up of 500 mL of 1.4 M C_{6}H_{5}NH_{2} and 230 mL of 2.3 M C_{6}H_{5}NH_{3}^{+}.

**Henderson-Hasselbalch Equation** deals with conjugate acid-base pairs and allows us to calculate pH of a buffer without the use of ICE Chart.

Concept #1: Henderson-Hasselbalch Equation

Example #1: Calculate the pH of a solution containing 2.0 M nitrous acid (HNO_{2}) and 1.48 M lithium nitrite (LiNO_{2}).

K_{a} = 4.6 x 10^{-4}.

Practice: The K_{b} of C_{6}H_{5}NH_{2} (aniline) is 3.9 × 10^{−}^{10}. Determine pH of a buffer solution made up of 500 mL of 1.4 M C_{6}H_{5}NH_{2} and 230 mL of 2.3 M C_{6}H_{5}NH_{3}^{+}.

Practice: Determine the buffer component concentration ratio (CB/WA) for a buffer with a pH of 4.7. K_{a} of boric acid (H_{3}BO_{3}) is 5.4 × 10^{−}^{10}.

Practice: Calculate mass of NaN_{3} that needs be added to 1.8 L of 0.35 M HN_{3} in order to make a buffer with a pH of 6.5. K_{a} of hydrazoic acid is 1.9 × 10^{−}^{5}.

Concept #2: Calculating Buffer Range

Example #2: Determine the buffering range of a solution containing lactic acid (K_{a} = 1.4 x 10^{-4}) and sodium lactate.

Practice: Which of the following weak acid-conjugate base combinations would result in an ideal buffer solution with a pH of 9.4?

a) formic acid (HCHO_{2}) and sodium formate (K_{a} = 1.8 x 10^{-4})

b) benzoic acid (HC_{7}H_{5}O_{2}) and potassium benzoate (K_{a} = 6.5 x 10^{-5})

c) hydrocyanic acid (HCN) and lithium cyanide (K_{a} = 4.9 x 10^{-10})

d) iodic acid (HIO_{3}) and sodium iodate (K_{a} = 1.7 x 10^{-1})