Experimental Techniques

Collection of Gases

Downward Delivery

• Used to collect gases denser than air
• E.g.:
  • Sulfur dioxide
  • Chlorine

Upward Delivery

• Used to collect gases less dense than air
• E.g.:
  • Hydrogen
  • Ammonia

Displacement of water

• Used to collect gas that is insoluble/slightly soluble in or unreactive with water
• E.g.:
  • Hydrogen
  • Carbon Dioxide
  • Oxygen

Drying Agent

• gas to be collected is often contaminated with water vapour and can be dried by passing it through a drying agent such as:
  • Concentrated sulfuric acid (Not suitable for alkaline gases)
  • Calcium oxide (Not suitable for acidic gases)
  • Anhydrous calcium chloride
  • Anhydrous copper(II) sulfate
• Anhydrous copper(II) sulfate may be used as an indicator for water vapour. It turns from white to blue in the presence of water.

Identification of Gases