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Preparing Gases

Chemical Concept Demonstrated

  • Chemical gas production


One of the following apparati should be built:  a 500-mL Erlenmeyer flask with a two-hole stopper to which a dropping funnel and a glass delivery tube have been attached, or a 500-mL filter flask fitted with a one-hole stopper and a dropping funnel.

Collection should take place via the downward displacement of water (if the gas doesn't react with water) or the downward or upward displacement of air (depending on the relative density of the gas).  Gas should be collected in a balloon to be easily accessible in a lecture demonstration (see 4.1 video and 4.2 demonstration sheet and video).

The following gases can be produced by the methods provided:

  • Acetylene (C2H2): Place 20 g CaCin the apparatus and add water at the rate of two to three drops per minute
  • Ammonia (NH3): Small amount: water to magnesium nitride (Mg2N2) / Large amount: Warm concentrated aqueous ammonia (drying tube required) or add concentrated aqueous ammonia to solid NaOH
  • Carbon Dioxide (CO2): Either add 6 M HCl to 20 g chalk, marble, limestone, or dolomite or evaporate dry ice.
  • Chlorine: Add ~1 g KMnOto concentrated HCl
  • Hydrogen (H2): React ~45 g mossy zinc or aluminum turnings with 6 M HCl
  • Nitrogen Oxide (NO): Add 6 M nitric acid to 20-30 g of copper turnings (note: this produces NO2 when the reaction first begins)
  • Nitrogen Dioxide (NO2): Add air to NO (tip: collect the product of the NO-producing reaction listed above by the upward displacement of air to produce NO2)
  • Oxygen: Add 3 g MnO2 or KMnOto 30 mL of 3% H2Oin the presence of a small quantity of sulfuric acid