Understanding the Terminology
* Normality (N): A measure of concentration that indicates the number of gram equivalents of a solute per liter of solution. In the case of ferrous ammonium sulfate (FeSO₄(NH₄)₂SO₄·6H₂O), the normality is related to the number of moles of iron (Fe²⁺) ions per liter of solution.
* Ferrous Ammonium Sulfate (FAS): The chemical formula is FeSO₄(NH₄)₂SO₄·6H₂O. It's a double salt that's commonly used in analytical chemistry.
Procedure
1. Calculate the Mass of Ferrous Ammonium Sulfate:
* Molecular Weight (MW) of FAS: 392.14 g/mol
* Equivalent Weight (EW) of FAS: MW/Number of replaceable hydrogen ions = 392.14 g/mol / 1 = 392.14 g/eq (Since there's one Fe²⁺ ion per molecule of FAS)
* Mass of FAS needed: Normality (N) x Equivalent Weight (EW) x Volume of Solution (in Liters)
* For a 0.1 N solution and 1 liter of solution: 0.1 N * 392.14 g/eq * 1 L = 39.214 g
2. Dissolve the FAS:
* Weigh out 39.214 g of ferrous ammonium sulfate.
* Add the solid to a clean 1-liter volumetric flask.
* Slowly add distilled water to the flask while stirring until the FAS is completely dissolved.
* Add more distilled water to the flask until the solution reaches the 1-liter mark. Ensure the meniscus is at the mark when viewing at eye level.
3. Acidify the Solution (Optional but Recommended):
* To prevent oxidation of ferrous ions (Fe²⁺) to ferric ions (Fe³⁺), add a small amount of dilute sulfuric acid (H₂SO₄) to the solution. Approximately 1 mL of concentrated sulfuric acid per liter of solution should suffice.
Important Notes:
* Use high-purity ferrous ammonium sulfate: Ensure it's a reagent-grade chemical.
* Distilled or deionized water: Use high-quality water to avoid introducing impurities.
* Stir thoroughly: Make sure the FAS dissolves completely and the solution is homogeneous.
* Store properly: Store the prepared solution in a tightly sealed amber glass bottle to minimize exposure to light and air, which can cause oxidation.
* Standardize the solution: For accurate analytical work, it's crucial to standardize the solution using a known standard like potassium permanganate.
Safety Precautions:
* Wear appropriate personal protective equipment (PPE) such as gloves, lab coat, and eye protection.
* Work in a well-ventilated area.
* Handle sulfuric acid with care. It is corrosive.
If you have any questions or need further clarification, please don't hesitate to ask!
