Question

Calculate the pH at the stoichiometric point when 25 mL of 0.081M formic acid is titrated with 0.34 M NaOH.

Calculate the pH at the stoichiometric point when 50 mL of 0.091 M pyridine is titrated with 0.35 M HCl.

Calculate the pH at the stoichiometric point when 25 mL of 0.088 M nitric acid is titrated with 0.30 M NaOH.

Answer 1

1)

millimoles of HCOOH = 25 x 0.081 = 2.025

at stoichiometric point :

millimoles of acid = millimoles of base

2.025 = 0.34 x V

V = 5.96 mL

here only salt remain. this salt is from weak acid and strong base . so pH > 7

[salt] = 2.025 / (25 + 5.56) = 0.0654 M

pH = 7 + 1/2 (pKa + log C)

     = 7 + 1/2 (3.74 + log 0.0654)

     = 8.28

pH = 8.28

2)

similarly as above

pH = 3.19

3)

this is a salt of strong acid and strong base . so pH = 7

pH = 7.00