Aluminum potassium sulfate Stock Solution

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Stock Solution Preparation Guide – Potassium Alum (Aluminum Potassium Sulfate, KAl(SO₄)₂·12H₂O)

Potassium alum (aluminum potassium sulfate dodecahydrate) is a crystalline inorganic salt that dissolves readily in water to form acidic solutions. It is commonly used in analytical chemistry, water treatment, and as a reagent in laboratory protocols. The hydrated form with 12 molecules of water (KAl(SO₄)₂·12H₂O, MW = 474.39 g/mol) is preferred for solution preparation because it is stable and easy to weigh.

Objective

Preparation of a defined‑concentration stock solution of potassium alum (e.g., 1 M solution).

Composition

• Potassium alum (KAl(SO₄)₂·12H₂O) aqueous solution of desired molarity

Required Materials

• Potassium alum (KAl(SO₄)₂·12H₂O)
• Deionized or distilled water
• Analytical balance
• Beaker or flask
• Volumetric flask or graduated cylinder
• Stirring rod or magnetic stirrer
• Personal protective equipment (gloves, goggles, lab coat)

Procedure

• Step 1
  Determine the target concentration. For a 1 M solution: weigh **474.39 g** of potassium alum (KAl(SO₄)₂·12H₂O) for a final volume of **1 L**. Scale the mass appropriately for other volumes (e.g., **47.439 g** for 100 mL).
• Step 2
  Place the weighed potassium alum into a beaker containing approximately **80% of the final volume** of deionized water. Stir with a glass rod or magnetic stirrer until completely dissolved.
• Step 3
  Transfer the dissolved solution into a volumetric flask. Rinse the beaker with small amounts of deionized water, adding the rinses to the volumetric flask. Bring the total volume up to the desired final volume (e.g., 1 L). Mix thoroughly.
• Step 4 (Optional)
  If a sterile solution is required, filter through a **0.22 µm** membrane into a sterile container or sterilize by autoclaving where appropriate.

Note: Solutions of potassium alum are acidic in nature (pH typically around 3.0–3.5 at moderate concentrations). Label the stock solution container with concentration and preparation date, and store it in a sealed, appropriately‑labeled vessel.

Available Reagents