What is the pH of the resulting solution? Assume complete ionisation of H2SO4 and HSO4-

Question

Two aqueous solutions are mixed: 50.0mL of 0.0150 M H2SO4 and 50.ml of 0.0385 M NaOH. What is the pH of the resulting solution? Assume complete ionization of H2SO4 and H2SO4-

Answer 1

To solve this problem, first calculate the total number of mmoles of H⁺ and OH^-:

 

mmol H⁺ = (50.0 mL soln)(0.0150 mmol H₂SO₄ / mL soln)(2 mmol H⁺ / mmol H₂SO₄) = 1.50 mmol H⁺

 

mmol OH^- = (50.0 mL soln)(0.0385 mmol OH^- / mL soln) = 1.925 mmol OH^-

 

Because the amount of OH^- significantly exceeds the amount of H⁺, the pH of the solution will be determined by the amount of excess OH^-.

 

At equilibrium, [OH^-] = (1.925 - 1.5 mmol) / (100.0 mL soln) = 0.00425 M

 

pOH = -log(.00425) = 2.37

pH = 14 - pOH = 14- 2.37 = 11.63