Question

Calculate the pH during the titration of 30.00 mL of 0.1000 M HCOOH(aq) with 0.1000 M NaOH(aq) after 29.3 mL of the base have been added. Ka of formic acid = 1.8 x 10-4.

Answer 1

Answer:

3.336.

Explanation:

Herein, the no. of millimoles of the acid (HCOOH) is more than that of the base (NaOH).

So, concentration of excess acid = [(NV)acid - (NV)base]/V total = [(30.0 mL)(0.1 M) - (29.3 mL)(0.1 M)]/(59.3 mL) = 1.18 x 10⁻³ M.

For weak acids; [H⁺] = √Ka.C = √(1.8 x 10⁻⁴)(1.18 x 10⁻³ M) = 4.61 x 10⁻⁴ M.

∵ pH = - log[H⁺].

∴ pH = - log(4.61 x 10⁻⁴) = 3.336.