A solution of potassium permanganate (KMnO4) was standardised by titrating with 0.20 g of Na2C2O4 dissolved in 50 cm3 of acidified water. The endpoint was reached after 23.10 cm3 of solution had been added. Calculate the molar concentration of KMnO4 in the solution.
1. Write and balance the equation.
2MnO4^- + 5C2O4^2- + ? ==> 2Mn^2+ + 10CO2 +?
I didn't finish the entire equation (that is I omitted the H^+, electrons, and H2O) BUT I balanced the redox part and that's all you need.
2. mols Na2C2O4 = grams/molar mass = ?
3. Using the coefficients in the balanced equation, convert mols C2O4^2- to mols MnO4^-. That's ?mols Na2C2O4 x (2 mols KMnO4/5 mols Na2C2O4) = ?
4. Then M KMnO4 = mols KMnO4/L KMnO4
To calculate the molar concentration of potassium permanganate (KMnO4) in the solution, we need to use the balanced chemical equation between KMnO4 and Na2C2O4.
The balanced equation is as follows:
2 KMnO4 + 5 Na2C2O4 + 8 H2SO4 → K2SO4 + 2 MnSO4 + 10 CO2 + 5 Na2SO4 + 8 H2O
From the equation, we can see that 2 moles of KMnO4 reacts with 5 moles of Na2C2O4.
Given:
Mass of Na2C2O4 = 0.20 g
Volume of Na2C2O4 solution = 50 cm3
Volume of KMnO4 solution added = 23.10 cm3
Step 1: Calculate the number of moles of Na2C2O4.
Using the molecular weight of Na2C2O4 (molar mass):
Molar mass of Na2C2O4 = 2(22.99) + 2(12.01) + 4(16.00) = 134.00 g/mol
Number of moles of Na2C2O4 = Mass / Molar mass
Number of moles of Na2C2O4 = 0.20 g / 134.00 g/mol
Number of moles of Na2C2O4 = 0.00149 mol
Step 2: Use the stoichiometry of the balanced equation to find the number of moles of KMnO4.
According to the balanced equation, 2 moles of KMnO4 react with 5 moles of Na2C2O4.
So, the moles of KMnO4 will be in a 2:5 ratio with the moles of Na2C2O4.
Number of moles of KMnO4 = (Number of moles of Na2C2O4) x (2 moles of KMnO4 / 5 moles of Na2C2O4)
Number of moles of KMnO4 = 0.00149 mol x (2 / 5)
Number of moles of KMnO4 = 0.000596 mol
Step 3: Calculate the molar concentration (Molarity) of KMnO4.
Molarity (M) is defined as moles of solute divided by the volume of the solution in liters.
Volume of KMnO4 solution added = 23.10 cm3 = 23.10 mL
Volume of KMnO4 solution added = 23.10 mL / 1000 = 0.02310 L
Molar concentration of KMnO4 = (Number of moles of KMnO4) / (Volume of KMnO4 solution added in liters)
Molar concentration of KMnO4 = 0.000596 mol / 0.02310 L
Molar concentration of KMnO4 = 0.0258 M
Therefore, the molar concentration of KMnO4 in the solution is 0.0258 M.