Example 2
• In order to determine the concentration of a commercial
sample of hydrogen peroxide (H2O2
), 15 mL of it was
diluted to 300 mL. Then 20 mL of diluted solution was
acidified and titrated with a 0.021 M potassium
permanganate solution (KMnO4). An average volume of
18.72 mL was required. Determine the concentration of
the original hydrogen peroxide.
First, let's calculate the number of moles of potassium permanganate that reacted with the hydrogen peroxide:
Moles of KMnO4 = Molarity of KMnO4 x Volume of KMnO4
Moles of KMnO4 = 0.021 M x 18.72 mL = 0.39312 mmol
Since the reaction between hydrogen peroxide and potassium permanganate is a redox reaction, we can use the stoichiometry of the reaction to determine the number of moles of hydrogen peroxide that reacted.
The balanced chemical equation for the reaction is:
5H2O2 + 2KMnO4 + 6H2SO4 → 5O2 + 2MnSO4 + K2SO4 + 8H2O
From the stoichiometry of the reaction, we can see that 2 moles of KMnO4 react with 5 moles of H2O2.
Moles of H2O2 = (0.39312 mmol KMnO4) x (5 mol H2O2 / 2 mol KMnO4) = 0.9828 mmol
Now, we can calculate the concentration of the original hydrogen peroxide solution:
0.9828 mmol H2O2 is present in 20 mL of diluted solution, which was originally 15 mL and further diluted to 300 mL. Thus, the 0.9828 mmol H2O2 is present in 300 mL of original solution.
Concentration of H2O2 = (0.9828 mmol / 300 mL) x 1000 = 3.276 x 10^-3 mol/L = 3.276 mM
Therefore, the concentration of the original hydrogen peroxide solution is 3.276 mM.