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The solubility of K₂SO₄ in various mixed solvent systems

The following five systems are considered on this page:

1. Methanol-K₂SO₄-H₂O at 60°C
2. Ethanol-K₂SO₄-H₂O at 25°C
3. 1-Propanol-K₂SO₄-H₂O at 45°C
4. i-Propanol-K₂SO₄-H₂O at 50°C
5. NH₃-K₂SO₄-H₂O at 60°C

The figures 1 to 5 show solubility isotherms for these five systems. The solubility isotherms describe compositions of each system in equilibrium with solid potassium sulfate.  In all these systems, K₂SO₄ is being salted out by the addition of an extra solvent. 'Salted out' means that the solubility decreases and an excess of salt precipitates. 

In the triangular diagrams shown below, lines of constant mass % potassium sulfate are lines parallel to the right hand side of the triangle. This side is opposite to the corner representing pure K₂SO₄ and represents potassium sulfate free solutions. A decreasing solubility of K₂SO₄ is characterized by solubility lines getting closer to the right side of the diagram. 

Of the five solvents added one by one in each of the five diagrams, ammonia has a stronger salting out effect on K₂SO₄ than the four alcohols. In all the depicted diagrams, the red circles represent experimental data while the solubility equilibrium lines were calculated with the Extended UNIQUAC model.

1. The Methanol-K₂SO₄-H₂O system at 60°C:

Figure 1: The Methanol-K₂SO₄-H₂O system at 60°C

2. Ethanol-K₂SO₄-H₂O at 25°C

Figure 2: The ethanol-K₂SO₄-H₂O system at 25°C

3. 1-Propanol-K₂SO₄-H₂O at 45°C

Figure 3: The 1-Propanol-K₂SO₄-H₂O system at 45°C

4. i-Propanol-K₂SO₄-H₂O at 50°C

Figure 4: The i-Propanol-K₂SO₄-H₂O system at 50°C

5. The NH₃-K₂SO₄-H₂O system at 60°C

Figure 5: The NH₃-K₂SO₄-H₂O system at 60°C