ZIMSEC O Level Combined Science Notes: An  experiment To show changes in shape and volume of iodine crystals when they are heated

Materials: evaporation dish/tin lid, glass filter funnel, burner, burner stand, one iodine crystal


  1. Place the iodine crystal into an evaporation dish
  2. Put the filter funnel upside down over the crystal
  3. Warm the crystals gently until the filter funnel is filled with iodine vapour
  4. NB Iodine vapour is dangerous so take precautions during the process
  5. Remove the burner and allow the iodine vapour to cool

Observations and results

  • The iodine crystal is gray in colour
  • When it is heated it sublimes (turns into a gas immediately) into a purple vapour
  • the vapour covers the entire filter funnel
  • when it is cooled it crystallizes on the surface of the filter funnel and on the evaporation dish


  • When the iodine is heated it sublimes into a gas
  • The gas fills the whole volume of the shape (inverted funnel)
  • This means gases occupy more volume than solids and liquids
  • When the iodine is heated it loses its shape and becomes a gas
  • Gases have no fixed shape they take up the entire shape of the container

To access more topics go to the Combined Science Notes page.