(40) GCSE Chemistry Revision "Required Practical 1: Making Soluble Salts"

Making Soluble Salts Using an Acid

Definition of Salts

  • A salt is formed by the reaction of an acid with a base, metal, or carbonate.

  • Example of a salt: Copper sulfate (CuSO₄).

Components of Salts

  • Positive Ion: Comes from the metal (e.g., copper ion Cu²⁺).

    • Sources of Positive Ions:

      • Metal itself: Copper (not reactive enough with dilute sulfuric acid).

      • Metal oxide: Copper oxide.

      • Metal hydroxide: Copper hydroxide.

      • Metal carbonate: Copper carbonate.

  • Negative Ion: Comes from the acid (e.g., sulfate ion SO₄²⁻).

    • Required Acid: Sulfuric acid.

Objective of the Practical

  • To make pure crystals of a soluble salt (e.g., copper sulfate).

  • Follow AQA specification for using either a metal oxide or a metal carbonate.

Materials Needed

  • Reactants:

    • Dilute sulfuric acid (limiting reactant).

    • Copper oxide (black powder).

  • Equipment:

    • Beaker, glass rod, spatula, filter funnel, filter paper, evaporating basin.

Steps to Make Soluble Salt Using Metal Oxide

  1. Prepare the Acid:

    • Start with a fixed amount of dilute sulfuric acid (important for ensuring no acid remains).

  2. Heating the Acid:

    • Gently heat the acid until it’s almost boiling (avoid boiling to prevent bubbling over).

  3. Add Copper Oxide:

    • Gradually add small amounts of copper oxide while stirring with a glass rod.

    • The copper oxide reacts, forming a blue copper sulfate solution.

  4. Check Reaction Completion:

    • Continue adding copper oxide until the solution remains clear blue and some powder remains after stirring (indicating complete reaction and neutral solution).

Remove Unreacted Material

  • Filtration:

    • Use a filter funnel and filter paper to filter out the unreacted copper oxide (insoluble).

Crystallization Process

  1. Evaporation:

    • Pour the copper sulfate solution into an evaporating basin.

    • Heat gently over a beaker of boiling water until about half the solution remains.

  2. Crystallization:

    • Leave the solution in a cool place for 24 hours to allow copper sulfate crystals to form.

  3. Harvest Crystals:

    • After crystals form, scrape them onto a paper towel and gently pat dry to obtain pure dry copper sulfate crystals.

Conclusion

  • Understand each step of making a soluble salt with acid (a practical question likely in exams).