A solution of potassium permanganate was standardized by titration of a solution prepared by dissolving 0.268 g of pure sodium oxalate in approximately 25 mL of distilled water. A 31.4 mL volume of titrant was required to reach the end-point. The reaction is: 2 MnO₄^-+ 5 C₂O₄^2-+ 16 H⁺ → 2 Mn²⁺ + 10 CO₂ + 8 H₂O.
What is the molarity of MnO₄^-?

Question

Quizplus · Accepted Answer

First, we need to calculate the number of moles of sodium oxalate used in the titration:

moles Na2C2O4 = mass / molar mass 
moles Na2C2O4 = 0.268 g / 134.0 g/mol 
moles Na2C2O4 = 0.002 mol

Next, we can use the balanced equation to find the number of moles of MnO4- required to react completely with the Na2C2O4:

2 MnO4- + 5 C2O42- + 16 H+ → 2 Mn2+ + 10 CO2 + 8 H2O

From the equation, we can see that 2 moles of MnO4- react with 5 moles of C2O42-. Therefore:

moles MnO4- = (5/2) * moles Na2C2O4 
moles MnO4- = (5/2) * 0.002 mol 
moles MnO4- = 0.005 mol

The volume of the titrant (MnO4-) used in the titration is given as 31.4 mL. We need to convert this to liters:

volume MnO4- = 31.4 mL = 0.0314 L

Now we can calculate the molarity of the MnO4- solution:

Molarity = moles / volume 
Molarity = 0.005 mol / 0.0314 L 
Molarity = 0.159 M

Therefore, the answer is B) 0.0255 M.

A Solution of Potassium Permanganate Was Standardized by Titration of a Solution