Crystallization of impure sample of any one of the following: Alum, Copper Sulphate, Benzoic Acid

Let us learn to know the process of Purification of Compounds by Crystallisation of Impure Sample. Purification of compounds is done using various methods like evaporation, decantation, filtration, distillation, and crystallization. Crystallization is one of the purification techniques which follows the process of purification substances by removing unwanted by-products.

Aim:

Purification of the impure samples like Copper Sulphate, Alum, Benzoic Acid and Iron Sulphate by the process of crystallization.

Materials Required:

50 mL capacity Beaker, filtration unit, watch glass, kerosene burner and CuSO4 .5H20

Experimental setup:

Crystallization of impure sample Experimental setup

The procedure of crystallization of copper sulphate:

  1. Prepare a clear solution of copper sulphate.
  2. Dissolve 0.8g of CuSO4.5H20 in about 8 mL of water and add 1-2 drops about 6 mL H2SO4 to it.
  3. Heat the solution for a while and filter it using a filtration unit.
  4. Transfer the solution from filtration unit to another beaker and Allow it to cool to room temperature.
  5. The crystals will appear.
  6. Filter, wash these crystals and let it dry
  7. Weigh the crystals and report the yield.

The procedure of crystallization of Alum:

  1. First, prepare a clear solution of alum by dissolving 1g of Alum sample in about 5 mL of water.
  2. To this solution add 2 drops of H2SO4.
  3. Heat the solution for a while and filter it using a filtration unit.
  4. Transfer the solution from filtration unit to another beaker and allow it to cool down to room temperature.
  5. Formation of the crystals is witnessed.
  6. Filter and wash these crystals and allow it to dry
  7. Weigh the crystals and report the yield.

The procedure of crystallization of Benzoic Acid:

  1. Make a clear solution of benzoic acid by dissolving 0.5g of the benzoic acid sample in about 8 mL of water.
  2. Heat the solution for a while and filter it using a filtration unit.
  3. Transfer the solution from filtration unit to another beaker and allow it to cool down to room temperature.
  4. Formation of benzoic acid crystals is seen.
  5. Filter and wash benzoic acid crystals and allow it to dry
  6. Weigh the crystals and report the yield.

The procedure of crystallization of Iron Sulphate:

  1. A clear solution of Iron Sulphate is prepared by dissolving 0.5g of Iron Sulphate sample in about 3 mL of water.
  2. To this solution add 3 drops of H2SO4.
  3. Heat the solution for a while and filter it using a general filtration method.
  4. Transfer the filtered solution to another beaker and allow it to cool down to room temperature.
  5. Formation of the Iron Sulphate crystals is clearly seen.
  6. Filter these crystals and wash it well without any residue. Allow it to dry completely.
  7. Weigh the crystals and report the yield.

Precautions to be taken during the experiment:

  • Ensure that the crystals are washed well.
  • Avoid overheating of the solution
  • The filtrate should be evaporated slowly by gentle heating of the solution.
  • The solution should be cooled slowly and do not use any rapid cooling procedures.

Observation

Weight of copper sulphate obtained

Weight of alum obtained

Weight of benzoic acid obtained

Weight of iron sulphate obtained

Viva Voice:

  1. List various methods of purification of a substance
    • Evaporation
    • Crystallization
    • Decantation
    • Filtration
    • Distillation
  2. Why is sulphuric acid added for dilute copper sulphate solution?

    Sulphuric acid is added to avoid the hydrolysis of copper sulphate.

  3. Does the process of crystallization is affected by increasing the temperature

    Yes

  4. What is the shape of copper sulphate crystals formed?

    triclinic shape

  5. What is the color of benzoic acid crystals formed?

    Color of benzoic acid crystals formed is opaque white color