Question

One way to determine the pH of a solution is to measure the concentration of the acid and base forms of the indicator colorimetrically. In a solution where bromocresol green ( pKa = 4.66) is used as the indicator, what is the pH of the solution when the concentration ratio of the acid to base form of the indicator is 2.49. pH=

Answer 1

Answer:

pH = 4.26

Explanation:

Bromocresol green is a commonly used pH indicator. The concentration ratio of the acid form to base form explains its color, which reflects the pH of the medium.

C₂₁H₁₄Br₄O₅S + H₂O ⇄ C₂₁H₁₃Br₄O₅S⁻ + H₃O⁺

      acid                       conjugate base

We can calculate the pH through Henderson-Hasselbalch's equation:

$pH=pKa+log(\frac{[base]}{[acid]} )=4.66+log(\frac{1}{2.49} )=4.26$