Question

Calculate the % of MnO2 in a sample of pyrolusite ore, 1.5 g which was made to react with 10 g of Mohr’s salt (FeSO4.(NH4)2SO4. 6H2O) and dilute H2SO4. MnO2 was converted 2 Mn2+ . After the reaction the solution was diluted to 250 ml and 50 ml of this solution, when titrated with 0.1 N K2Cr2O7, required 10 ml of the dichromate solution.​

Answer 1

Thus the percentage of purity is 72.67 %

Explanation:

• Milli equivalent for 50 ml solution = 1 m
• Milli equivalent for 250 ml solution = 5 m
• Milli equivalent of mohr salt = 0.0255*1000=25.5
• Difference in milli equivalent gives milli equivalent of MnO2
• Milli equivalent of MnO2 = 20.5

Moles x 2000 = 20.5

Moles = 0.01025

w / 86.93 = 0.01025

w = 1.09 g

Purity percentage = 1.09 / 1.5 x 100

Purity percentage  = 72.67 %

Thus the percentage of purity is 72.67 %