25.00 mL of a H2SO4 solution with an unknown concentration was titrated to a phenolphthalein endpoint with 41.85 mL of a 0.1299 M NaOH solution.

Question

What is the concentration of the H₂SO₄ solution?

[H₂SO4]=?

Answer 1

Write the correctly balanced equation for the reaction taking place:

H₂SO₄ + 2NaOH ==> Na₂SO₄ + 2H₂O .. balanced equation

To find the concentration of H₂SO₄, we need to first find the moles of H₂SO₄. We do this by finding the moles of NaOH used to reach the end point, and then use the mol ratio of 2:1 NaOH:H₂SO₄.

moles NaOH used = 41.85 ml x 1 L / 1000 ml x 0.1299 mol / L = 5.436x10^-3 mols NaOH

moles H₂SO₄ = 5.436x10^-3 mols NaOH x 1 mol H₂SO₄ / 2 mol NaOH = 2.718x10^-3 mol H₂SO₄

Concentration H₂SO₄ is moles / liter

2.718x10^-3 mol H₂SO₄ / 25.00 ml x 1000 ml / L = 0.1087 mol / L