Question

6.An acid-base indicator is usually a weak acid with a characteristic color in the protonated and deprotonated forms. Because bromocresol green is an acid, it is convenient to represent its rather complex formula as HBCG. HBCG ionizes in water according to the following equation:HBCG + H2O = BCG- + H3O+ (yellow)(blue)The Ka (the equilibrium constant for the acid) expression is: Ka=[BCG−][H3O+][HBCG]When [BCG-] = [HBCG], then Ka = [H3O+]. If you know the pH of the solution, then the [H3O+] and Ka can be determined. What would be the color of the solution if there were equal concentrations of HBCG and BCG-?Solution Color: _______________What is the pH at the first appearance of this color?Solution pH: __________What is an estimate for the Ka for bromocresol green? Show your work to get full credit

Answer 1

Answer:

At equal concentration of HBCG and BCG^-, the colour is green. This colour first appears at pH = 3.8

Explanation:

HBCG is an indicator that is prepared by dissolving the solid in ethanol.

Since

Ka=[BCG−][H3O+][HBCG]When [BCG-] = [HBCG], then Ka = [H3O+].

If pH = 3.8

Ka= [H3O+] = -antilog pH = -antilog (3.8)

Ka= 1.58 ×10^-4