The most effective way to separate copper sulphate from its concentrated solution is through crystallization, specifically by controlled evaporation.
Here's a breakdown of the process:
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Preparation: Start with the concentrated copper sulphate solution. If there are any undissolved impurities, filter the solution to remove them.
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Evaporation: Gently heat the solution to evaporate the water. This can be done using a water bath or a hot plate set to a low temperature. Avoid boiling the solution vigorously, as this can lead to small, poorly formed crystals. The goal is to evaporate the water slowly.
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Saturation Point: As water evaporates, the concentration of copper sulphate increases. Continue evaporating until the solution reaches its saturation point at the current temperature. You'll know it's approaching saturation when small crystals start to form on the surface or the sides of the container.
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Cooling and Crystallization: Stop heating and allow the solution to cool slowly. Cooling slowly encourages the formation of larger, purer crystals. Avoid disturbing the solution during cooling, as this can also lead to the formation of small crystals. The slower the cooling, the larger and more defined the crystals will be.
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Filtration: Once the solution is cooled and significant crystals have formed, carefully filter the mixture. Use filter paper and a funnel to separate the copper sulphate crystals from the remaining solution (called the mother liquor).
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Washing: Gently wash the collected crystals with a small amount of cold distilled water to remove any remaining mother liquor that may be adhering to their surface.
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Drying: Spread the crystals on a filter paper or absorbent paper and allow them to air dry. This will remove any remaining moisture.
Why this method works:
- Solubility and Temperature: Copper sulphate's solubility in water changes with temperature. As the solution cools, the solubility decreases. The copper sulphate becomes less soluble, causing it to precipitate out of the solution and form crystals.
- Evaporation Concentrates the Solute: Evaporation removes the solvent (water), increasing the concentration of copper sulphate until it exceeds the solubility limit at the current temperature, thus initiating crystallization.
Summary:
Controlled evaporation followed by slow cooling allows copper sulphate to crystallize out of its concentrated solution. This method utilizes the principle that the solubility of copper sulphate decreases with temperature. The resulting crystals can then be separated by filtration, washed, and dried.
