To prepare a ferrous ammonium sulphate solution, you'll need to dissolve a specific amount of ferrous ammonium sulphate in water with the addition of dilute sulfuric acid to prevent hydrolysis. Here's a step-by-step guide:
Materials:
- Ferrous Ammonium Sulphate crystals (Fe(NH₄)₂(SO₄)₂·6H₂O)
- Distilled water
- Dilute Sulfuric Acid (H₂SO₄)
- Beaker (250 ml is a good size)
- Stirring rod
- Weighing scale
- Measuring cylinder
Procedure:
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Calculate the required amount of Ferrous Ammonium Sulphate: Determine the concentration (e.g., molarity or percentage) and volume of the solution you need. Then, calculate the mass of ferrous ammonium sulphate required using the formula:
Mass = (Desired Concentration) x (Desired Volume) x (Molar Mass). The molar mass of ferrous ammonium sulphate hexahydrate is approximately 392.14 g/mol. For example, to make approximately 200 mL of a solution using the values found in the prompt, weigh out approximately 7g of FeSO4 (which should instead be Ferrous Ammonium Sulphate) and 3.5g of Ammonium Sulphate. Note: Ammonium Sulphate addition isn't usually required and the prompt most likely refers to Ferrous Ammonium Sulphate only. -
Weigh the Ferrous Ammonium Sulphate: Accurately weigh out the calculated amount of ferrous ammonium sulphate crystals.
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Prepare the Dilute Sulfuric Acid (Important): In a separate container, carefully dilute concentrated sulfuric acid with distilled water. Always add acid to water, not water to acid, to avoid splattering. A concentration of 1M sulfuric acid is suitable. According to the prompt approximately 2.3 mL of dilute sulfuric acid should be used, depending on the final volume.
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Dissolve the Ferrous Ammonium Sulphate:
- Add approximately 150 mL of distilled water to the beaker.
- Add the weighed ferrous ammonium sulphate crystals to the beaker.
- Add the calculated amount of dilute sulfuric acid (e.g., 2.3 mL if following the prompts amounts)
- Stir the solution gently with a stirring rod until the crystals are completely dissolved. Heating the water slightly (e.g., to 40-50°C) can help the dissolving process.
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Adjust the Volume (If Necessary): Once the crystals are dissolved, add distilled water to the beaker until the solution reaches the desired final volume (e.g., 200 mL).
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Mix Thoroughly: Stir the solution well to ensure it is homogeneous.
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Storage: Store the ferrous ammonium sulphate solution in a clean, airtight container, preferably in a cool, dark place. This helps to minimize oxidation of the ferrous ions (Fe²⁺) to ferric ions (Fe³⁺).
Why Sulfuric Acid is Added:
The addition of dilute sulfuric acid is crucial to prevent hydrolysis of the ferrous ions (Fe²⁺) and the formation of insoluble iron hydroxides, which would make the solution cloudy and affect its concentration. The acid maintains a low pH, which favors the ferrous ions remaining in solution.
Example:
Let's say you want to prepare 200 mL of a 0.1 M ferrous ammonium sulphate solution.
- Calculate Mass: Mass = 0.1 mol/L 0.2 L 392.14 g/mol = 7.84 g (approximately).
- Weigh out 7.84 g of ferrous ammonium sulphate.
- Follow the remaining steps above using this weighed amount and 2.3mL of dilute sulfuric acid.
