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.

Question

Marcos Townsend

Chemistry

14 September, 14:27

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.

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Gustavo Parsons · Answer 1

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.