A saturated solution of sodium sulphate refers to a solution where the maximum amount of sodium sulphate has been dissolved in a given amount of solvent (typically water) at a specific temperature. Once a solution becomes saturated, no more solute can dissolve, and any additional solute added will typically remain as a solid at the bottom or precipitate out of the solution.
Understanding Saturated Solutions
A saturated solution represents the equilibrium state between a dissolved solute and undissolved solute. In simpler terms, it's a solution holding the maximum possible amount of a substance that can be dissolved under specific conditions, particularly temperature and pressure.
When discussing sodium sulphate (Na₂SO₄) solutions, saturation is determined by how many grams of the salt can dissolve in a specific quantity of water.
Sodium Sulphate Saturation at 20°C
Based on the provided reference, we know the specific saturation point for anhydrous sodium sulphate at a common laboratory temperature:
- For sodium sulfate at 20°C, a saturated solution occurs at 19.06 g anhydrous salt per 100 g H₂O.
This means that at 20°C, you can dissolve up to 19.06 grams of anhydrous sodium sulphate in every 100 grams of water.
Practical Implications
Understanding the saturation point is crucial in various applications:
- Preparing Solutions: If you need a saturated sodium sulphate solution at 20°C, you would add slightly more than 19.06 g of anhydrous Na₂SO₄ to 100 g of water and stir until no more solid dissolves.
- Crystallization: When a saturated solution cools (and solubility decreases) or solvent evaporates, the excess dissolved solute comes out of the solution as solid crystals. For sodium sulphate, solubility varies significantly with temperature, making crystallization a common process.
- Chemical Reactions: The concentration of a saturated solution defines the upper limit of how much sodium sulphate is available to participate in a reaction at that temperature.
Consider this:
- If you add only 10 grams of anhydrous Na₂SO₄ to 100 grams of water at 20°C, the solution is unsaturated. You could dissolve more salt.
- If you add 25 grams of anhydrous Na₂SO₄ to 100 grams of water at 20°C, 19.06 grams will dissolve, and approximately 5.94 grams will remain as undissolved solid, resulting in a saturated solution in contact with excess solid.
The solubility value (19.06 g/100 g H₂O at 20°C) is a key characteristic defining the saturated solution of sodium sulphate under these specific conditions.
