Question

You need to determine the concentration of a sulfuric acid solution by titration with a standard sodium hydroxide solution. You have a 0.1126 M standard solution. You take a 25.00 mL sample of the original acid solution and dilute it to 250.0 mL. You then take a 10.00 mL sample of the dilute acid solution and titrate it with the standard solution. You need 14.59 mL of the standard solution to reach the endpoint. What is the concentration of the original acid solution?

Answer 1

Molar concentration of NaOH when diluted to 250 ml = 0.1126*25/250 = 0.01126 M

Let the molar concentration of the acid solution be M

Thus, moles of acid solution = molarity*volume of solution in litres = M*0.01

Moles of NaOH = molarity*volume of solution in litres = 0.01126*0.01459 = 0.00016

Now, 2NaOH + H₂SO₄ --------> Na₂SO₄ + 2H₂O

Thus, moles of NaOH = 2*moles of H₂SO₄ required for complete neutralisation

or, 0.00016 = 2*M*0.01

or, M = 0.0082 = Molarity of H₂SO₄