Sample Calculation for Percentage Purity of Oxalate

Given Data:
- Mass of impure sample = 0.5 g
- Volume of solution = 100 mL
- Volume of N/20 KMnO4 solution required for titration = 15 mL
- Concentration of N/20 KMnO4 solution = N/20 (where N is normality)

Step 1: Calculate the Molarity of N/20 KMnO4 Solution
The molarity of a solution is given by the formula:
Molarity (M) = (Normality (N) * Equivalent weight) / Volume (L)

The equivalent weight of KMnO4 is 158 g/mol.
Given that the solution is N/20, we can calculate the molarity as follows:
Molarity (M) = (N/20 * 158 g/mol) / 1 L
Molarity (M) = N/20 * 7.9 g/L

Step 2: Calculate the Number of Moles of KMnO4 used in the Titration
Moles = Molarity (M) * Volume (L)
Moles of KMnO4 = (N/20 * 7.9 g/L) * 0.015 L

Step 3: Calculate the Number of Moles of Oxalate in the Sample
The reaction between oxalate and KMnO4 is as follows:
5C2O4^2- + 2MnO4^- + 16H+ -> 10CO2 + 2Mn^2+ + 8H2O

From the balanced chemical equation, we can see that 2 moles of KMnO4 react with 5 moles of oxalate.
Therefore, the number of moles of oxalate = (2/5) * Moles of KMnO4

Step 4: Calculate the Percentage Purity of the Sample
The percentage purity of the sample is given by the formula:
Percentage Purity = (Mass of pure oxalate / Mass of impure sample) * 100

To find the mass of pure oxalate, we need to know the molar mass of oxalate.
The molar mass of C2O4^2- = 2 * (12.01 g/mol) + 4 * (16.00 g/mol) = 88.02 g/mol

Mass of pure oxalate = Number of moles of oxalate * Molar mass of oxalate
Mass of pure oxalate = [(2/5) * Moles of KMnO4] * 88.02 g/mol

Percentage Purity = (Mass of pure oxalate / Mass of impure sample) * 100
Percentage Purity = {[(2/5) * Moles of KMnO4] * 88.02 g/mol / 0.5 g} * 100

Simplifying the expression will give you the percentage purity of the sample.

Note: The purity percentage obtained from this calculation assumes that the impurities in the sample do not react with KMnO4. If the impurities are known, their effect on the calculation should be considered.