Aluminium sulfate Stock Solution

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Stock Solution Preparation Guide – Aluminium Sulfate (Al₂(SO₄)₃) Solution

Aluminium sulfate is commonly available in hydrated forms such as hexadecahydrate (Al₂(SO₄)₃·16H₂O) and octadecahydrate (Al₂(SO₄)₃·18H₂O) or as the anhydrous salt. In laboratory settings, the octadecahydrate form is often used to prepare defined‑concentration stock solutions because of its stable crystalline state.

Objective

Preparation of a defined concentration stock solution of aluminium sulfate (e.g., 1 M).

Composition

• Aluminium sulfate (Al₂(SO₄)₃) aqueous solution at the desired molarity

Required Materials

• Aluminium sulfate octadecahydrate (Al₂(SO₄)₃·18H₂O)
• Deionized or distilled water
• Analytical balance
• Beaker or flask
• Volumetric flask or graduated cylinder
• Magnetic stirrer or glass stirring rod
• Personal protective equipment (gloves, goggles, lab coat)

Procedure

• Step 1
  Decide the target concentration (e.g., 1 M). For a 1 M solution of aluminium sulfate octadecahydrate: calculate and weigh the required mass (for 1 L, ~666.44 g Al₂(SO₄)₃·18H₂O).
• Step 2
  Add the weighed aluminium sulfate to ~700 mL of deionized water in a beaker. Place on a magnetic stirrer and stir until completely dissolved. Gentle warming (not exceeding 40 °C) may help dissolution.
• Step 3
  Transfer the dissolved solution to a volumetric flask. Rinse the beaker with small amounts of deionized water and add the rinses to the volumetric flask. Add water to bring the solution to the final volume (e.g., 1 L). Mix thoroughly.
• Step 4 (Optional)
  For sterile applications, filter the solution through a 0.22 µm membrane filter into a sterile container or autoclave if appropriate for your use case.

Note: Hydrated salts are preferable for accurate weighing. Anhydrous aluminium sulfate is hygroscopic and unsuitable for precise solution preparation without accounting for water uptake. Store the finished stock in a sealed container with a clear label indicating concentration and date.

Available Reagents