How would you make a soluble salt such as copper sulphate?

You can make copper sulphate, a soluble salt, through a reaction between an insoluble copper compound (like copper oxide or copper carbonate) and sulphuric acid. The process involves neutralization, filtration, and crystallization.

Steps to Prepare Copper Sulphate

Here's a detailed method for producing copper sulphate crystals:

1. Reacting the Insoluble Base with Acid:

   • Add powdered copper oxide (CuO) or copper carbonate (CuCO₃) to dilute sulphuric acid (H₂SO₄) in a beaker. Use a spatula and add it gradually while stirring continuously with a glass rod.
   • The reaction will produce copper sulphate solution (CuSO₄) and water (H₂O) or carbon dioxide (CO₂) depending on whether copper oxide or copper carbonate is used.
     • CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)
     • CuCO₃(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l) + CO₂(g)
   • Continue adding the copper oxide or copper carbonate until it is in excess. This means that some solid remains unreacted at the bottom of the beaker. This ensures all the sulphuric acid has reacted.

2. Filtering the Excess Solid:

   • Set up a filtration apparatus using a filter funnel and filter paper.
   • Carefully filter the mixture to remove the unreacted copper oxide or copper carbonate. The filtrate (the liquid that passes through the filter paper) will contain the copper sulphate solution.

3. Evaporating the Solution:

   • Pour the copper sulphate solution into an evaporating dish.
   • Heat the solution using a water bath to gently evaporate the water. Important: Avoid direct heating with a Bunsen burner to prevent the copper sulphate from decomposing. The water bath provides controlled, even heating.
   • Continue heating until the solution is saturated. You can test for saturation by dipping a cold glass rod into the solution; if small crystals form on the rod, the solution is saturated.

4. Crystallization:

   • Turn off the heat and allow the saturated solution to cool slowly.
   • As the solution cools, copper sulphate crystals will form. The slower the cooling process, the larger and purer the crystals will be.
   • Leave the solution undisturbed at room temperature for one or two days to allow maximum crystal growth.

5. Drying the Crystals:

   • Carefully pour off the remaining solution (the mother liquor) without disturbing the crystals.
   • Wash the crystals with a small amount of distilled water to remove any impurities on the surface.
   • Dry the crystals by gently pressing them between sheets of filter paper. You can also leave them to air dry in a warm place.

By following these steps, you can successfully prepare copper sulphate crystals from an insoluble copper compound and sulphuric acid.