M

Practical Work

Soluble salt formation

Steps to prepare copper(II) sulfate crystals:

  1. Add excess copper(II) oxide to dilute sulfuric acid and dissolve (heating in a water bath if needed).

  2. Filter the solution to remove unreacted solid, leaving a blue copper(II) sulfate solution.

  3. Evaporate half the water by heating, then allow the remaining solution to cool and evaporate slowly over several days to form blue crystals.

  4. Slow evaporation = larger crystals; fast evaporation produces white anhydrous copper(II) sulfate.

Reaction equation:
H2SO4+CuO→CuSO4+H2O

Insoluble salt formation

  • Insoluble salts are made by precipitation reactions, where an insoluble solid forms when two solutions mix.

  • Example: Silver nitrate + halide solution forms a precipitate.

  • Lead nitrate + potassium iodide forms bright yellow lead(II) iodide, used to test for lead ions:

    • Reaction:
      Pb(NO3)2(aq)+2KI(aq)→PbI2(s)+2KNO3(aq)

  • The precipitate is separated by filtration and dried in an oven or on a windowsill.

Gravimetric Analysis

This practical involves using gravimetric analysis to determine the molar mass and concentration of an unknown chloride. The key steps include:

  1. Weighing around 0.3 g of the unknown chloride, and transfer it to a 250cm3 beaker.

  2. Dissolving it in deionised water and adding nitric acid.

  3. Adding silver nitrate (AgNO₃) to precipitate silver chloride (AgCl).

  4. Heating and then cooling the solution.

  5. Filtering, washing, and drying the precipitate.

  6. Weighing the dried AgCl to determine its mass.

The calculations involve:

  • Determining moles of AgCl using mass / molar mass.

  • Since Ag⁺ and Cl⁻ react in a 1:1 ratio, the moles of AgCl equal the moles of chloride.

  • Calculating chloride concentration using moles / volume of solution.

Qualitative Analysis