An initial ph of 4.0 and an equivalence point at ph = 9.1 corresponds to a titration curve for a a. strong acid to which strong base is added b. strong base to which strong acid is added c. weak acid to which strong acid is added d. weak base to which strong acid is added e. weak acid to which strong base is added

Hello!

An initial pH of 4,0 and an equivalence point at pH=9,1 corresponds to a titration curve for a weak acid to which strong base is added

An example would be the titration of Acetic Acid (CH₃COOH) with Sodium Hydroxide (NaOH)

CH₃COOH + NaOH → CH₃COONa + H₂O

The initial pH will be acid because only the Acetic Acid is present. In the equivalence point, there are no CH₃COOH nor NaOH present, and the only species responsible for pH is CH₃COONa. This is a weak base, as evidenced by the following reaction:

CH₃COO⁻ + H₂O ⇄ CH₃COOH + OH⁻

So, in the equivalence point, the pH will be basic. These observations help us conclude that this titration is of a weak acid with a strong base. 

Have a nice day!