2.39 describe tests for the gasses

i Hydrogen (H+)

  1. Place lit splint in has, burning with a ‘squeaky pop’
  2. 2H (g) + O2 (g) –> H2O (l)

ii Oxygen (O2)

  1. Insert glowing splint and it should relight in the presence of oxygen

iii Carbon Dioxide (CO2)

  1. Bubbles through limewater and it should turn cloudy / milky / white in the presence of oxygen
  2. Ca(OH)2 (aq) + CO2 (g) –> CaCO3 (s) +H2O  (CaCO3 is the white precipitate of milky lime water)

iv Ammonia (NH4+)

  1. Damp red litmus turns blue
  2. NH3 (g) + H2O (l) ↔ NH4 + (aq) + OH- (aq)
  3. The hydroxide (water) ions are needed to dissolve the ammonia gas to make ammonium liquid. The damp universal indicator turns blue-meaning it’s an alkali substance

v Chlorine (Cl-)

  1. Damp litmus/universal indicator paper bleaches white
  2. Damp or moist starch-iodide paper turns blue (Cl2 (g) + 2I- (aq) –> 2Cl – (aq) + I2 (aq) – the iodine formed turns starch blue)
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