Reacting volumes of gases sim
Take a hydrocarbon and oxygen into two gas syringes, spark, cool, read, then take out the carbon dioxide with sodium hydroxide and read again. The volumes give the formula, because equal volumes of gases hold equal numbers of moles.
The mole: molar gas volume and reacting volumes of gases; the formula of a hydrocarbon from gas volumes · covers the GCSE (chemistry only, Higher), IGCSE (Supplement), O-Level topic
What the sim shows
Equal volumes of gases, at the same temperature and pressure, hold equal numbers of moles (24 dm³ per mole at room temperature and pressure). So the volumes of gases that react are in the same ratio as the numbers in the balanced equation. Take a measured volume of a hydrocarbon into syringe A and more oxygen than it needs into syringe B, and spark it. When it has cooled to room temperature, the water made is a liquid, so the volume falls. Push all the gas into one syringe and read it. Then pass it over aqueous sodium hydroxide, which takes out the carbon dioxide, and read again. The fall is the carbon dioxide made; the oxygen taken in minus what is left is the oxygen used. For CₓHᵧ + (x + y/4) O₂ → x CO₂ + (y/2) H₂O, the carbon dioxide made per volume of fuel is x, and the oxygen used per volume of fuel is x + y/4. Simpler modes: hydrogen with oxygen (2 : 1, all liquid water), carbon monoxide with oxygen (2 : 1, making carbon dioxide), and nitrogen with hydrogen making ammonia (1 : 3 : 2). All volumes are read at room temperature and pressure. Model limits: every reaction goes all the way; the ammonia mode is a calculation only, since this apparatus cannot make ammonia (in industry it is made over hot iron, and only part of it reacts: an equilibrium); readings are to the nearest 1 cm³; the water's own tiny volume is ignored; the hot expansion after the spark is illustrative.
- Plungers: drag out to take in gas, in to push it across
- Sparking tube: the spark sets the gases off
- Sodium hydroxide takes out carbon dioxide
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