Objective
Study various states of matter and transition from one state to other
Materials required:
- Aluminum chloride OR camphor OR naphthalene balls
- Test tubes
- Cotton Plug/ cork
Procedure:
- Take 5g powdered sublimable solid in a test tube and close the test tube with cotton plug
- Heat the test tube slowly
- Cover the outer surface of the test tube with wet cotton to sublime the vapours quickly
Findings:
- A sublimable solid on heating directly get converted into vapours, that sublimes back on cooling directly into solid again on the walls of the funnel.
Conclusions:
- A sublimable solid on heating directly converts into gaseous state. How? Is it because of the high vapour pressure of the liquid state of the solid. The liquid state is practically non-existent
Theory:
- A change in state directly from solid to gas on heating without changing into liquid state, or vice-versa is called sublimation
- This process is an endothermic phase transition that occurs at a temperature and pressure below the triple point of the substance. Desublimation or deposition is the reverse of this process in which a gas is directly converted into solid-state
- Elements and compounds mainly possess three different states at various temperatures. The transition from solid state to gaseous state requires a transition of solid-state to liquid state and liquid state to a gaseous state. If solids possess sufficient vapour pressure at a particular temperature than they can directly sublime into the air. Solids which have high pressure at their triple point show sublimation. The triple point is the point at which the pressure and temperature of the substance are such that it can exist in all three states of matter simultaneously. The triple point is a characteristic point of a substance. There are various examples of sublimation which are experienced by us in our everyday life.
- The best example of sublimation is dry ice which is a frozen form of carbon dioxide. When dry ice gets exposed to air, dry ice directly changes its phase from solid-state to gaseous state which is visible as fog. Frozen carbon dioxide in its gaseous state is more stable than in its solid-state.
- Another well-known example of sublimation is naphthalene which is an organic compound. Naphthalene is usually found in pesticides such as mothball. This organic compound sublimes due to the presence of non-polar molecules that are held by Van Der Waals intermolecular forces. At a temperature of 176F naphthalene sublimes to form vapours. It desublimates at cool surfaces to form needle-like crystals.
