Question

Aqueous solutions containing approximately 3 percent(w/w) H2O2 are sold in drug stores as a disinfectant. Determination of the actual concentration of H2O2 in a bottle of peroxide solution was done by diluting 1.00 mL to 100 mL with water, acidifying with dilute H2SO4 and titrating with a 0.01231 M KMnO4 solution. If 41.92 mL of the permangate solution was needed to reach the end point of the titration, what is the actual molar concentration of the H2O2 solution? Hint: Balance the reaction first: MnO4 - + H2O2 -> Mn2+ + O2 using half reactions

Answer 1

Aqueous solutions containing approximately 3 percent(w/w) H2O2 are sold in drug stores as a disinfectant. Determination of the actual concentration of H2O2 in a bottle of peroxide solution was done by diluting 1.00 mL to 100 mL with water, acidifying with dilute H2SO4 and titrating with a 0.01231 M KMnO4 solution. If 41.92 mL of the permangate solution was needed to reach the end point of the titration, what is the actual molar concentration of the H2O2 solution? Hint: Balance the reaction first: MnO4 - + H2O2 -> Mn2+ + O2 using half reactions​

Balanced reaction

2KMnO4 + 5H₂O₂ + 3H₂SO₄ --> 2MnSO₄(aq) + K₂SO₄(aq) + 5O₂ + 8H₂O......................full reaction

2MnO4^- + 5H₂O₂ + 6H⁺ --> 2Mn²⁺ + 5O₂(g) + 8H₂O(l) =   .................................................ionic equation

Accordingly 1 equivalent of KMnO₄ oxidizes 2.5 equivalents of H₂O₂

Molarity of KMnO₄ ​solution used for titration = 0.01231 M

Volume of KMnO₄ ​solution used for titration = 41.92 ml

Volume of dilute H₂O₂ solution = 1 ml  

Number of Moles of KMnO₄ consumed = 0.01231​ M x 0.04192 L​ = 0.000516 M

So number of Moles of H2O2 in 1 ml = 0.000516 mM x 2.5 = 0.00129 M

That means molarity of the H2O2 solution = 0.00129 M

Since original 3% solution is diluted by 100 times then its cocentration will be 100 times higher compared to 1 ml solution used in the titration:

Hence the actual cocentration of H2O2 = 0.00129 M x 100 = 0.129 M