When 3.92 ~g of Mohr salt is dissolved in 100 ~mL of water, and titrated against KMnO ₄ solution, 20 ~mL of this solution required 18 ~mL of KMnO ₄ for complete oxidation. The strength of KMnO ₄ is: [Molar mass of Mohr salt is 392 ~g ~mol ⁻¹ and KMnO ₄ is 158 ~g ~mol ⁻¹ ]

Step-by-step solution

The molarity of the Mohr salt solution is calculated as follows: Moles of Mohr salt = 3.92 g 392 g mol ⁻¹ = 0.01 mol . Molarity of Mohr salt solution = 0.01 mol 0.1 L = 0.1 M . The reaction between KMnO ₄ and Mohr salt in acidic medium is: MnO ₄⁻ + 8 H ⁺ + 5 Fe ²⁺ Mn ²⁺ + 5 Fe ³⁺ + 4 H ₂ O . The n-factor for Mohr salt ( Fe ²⁺ Fe ³⁺ ) is 1, and for KMnO ₄ ( Mn ⁺⁷ Mn ⁺² ) is 5. Using the equivalence relation N₁ V₁ = N₂ V₂ for the titration of 20 mL of Mohr salt solution: N_ Mohr 20 mL = N_ KMnO ₄ 18 mL . Since N_ Moh