To prepare a 0.05 M solution of Mohr's salt and determine the molarity and strength of the given KMnO4 solution, follow these steps:
Preparation of 0.05 M Mohr's Salt Solution
- Calculate the mass required:
- Mohr's salt (NH4)2Fe(SO4)2·6H2O has a molar mass of approximately 392 g/mol.
- For 0.05 M solution in 1 L:
- Mass = Molarity × Molar mass = 0.05 mol/L × 392 g/mol = 19.6 g.
- Dissolve the salt:
- Weigh 19.6 g of Mohr's salt.
- Dissolve in distilled water and make up the volume to 1 L in a volumetric flask.
Titration with KMnO4 Solution
- Setup the titration:
- Use 25 mL of the prepared Mohr's salt solution in a conical flask.
- Add a few drops of sulfuric acid (H2SO4) to acidify the solution.
- Titrate with KMnO4:
- Fill a burette with the KMnO4 solution.
- Slowly add KMnO4 to the Mohr's salt solution until a permanent pink color appears, indicating the endpoint.
Calculating Molarity and Strength of KMnO4
- Use stoichiometry:
- The reaction between KMnO4 and Mohr's salt involves a 1:5 molar ratio:
- KMnO4 + 5(NH4)2Fe(SO4)2 → products.
- Determine moles of Mohr's salt:
- Moles = Molarity × Volume = 0.05 mol/L × 0.025 L = 0.00125 mol.
- Calculate moles of KMnO4:
- From the stoichiometry, moles of KMnO4 = 0.00125 mol / 5 = 0.00025 mol.
- Find molarity of KMnO4:
- If the volume of KMnO4 used is V mL, then:
- Molarity = moles/volume(L) = 0.00025 mol / (V/1000 L).
Strength of KMnO4 Solution
- Calculate strength:
- Strength (g/L) = Molarity × Molar mass of KMnO4 (158 g/mol).
- Strength = Molarity × 158 g/L.
By following these steps, you can accurately prepare the solution and determine the necessary concentrations for your analysis.