The components of the tris and acetate stock solutions are a

The components of the tris and acetate stock solutions are at equal concentrations, but the pH of the two solutions are different. Explain. Be sure to include a chemical reaction that represents the equilibria described by the Ka expression.

Solution

even concentration of Tris and acetate are equal we get different pH due to different Ka values of both repective acids

for acetic acid we have

CH3COOH (aq) <---> CH3COO-(aq) + H+ (aq) , Ka = 1.8 x 10^ -5

for TrisH+ we have

TrisH+ (aq) <---> Tris (aq) + H+ (aq) , Ka = 8.5 x 10^ -9

even though we have [CH3COOH] = [TrisH+] we get different values of H+ for each acid , this is because difference in Ka . Higher value of Ka incdicates more dissociation of acid to give more H+