collecting gas

• Measuring the rate of a chemical reaction

  1. Using a measuring cylinder

  2. Using a gas syringe
• 2 mol per decimeter cubed


  For every litre of water, 2 moles of hydrochloric acid are dissolved
• 1 mol per decimeter cubed


  For every litre of water, 1 mole of hydrochloric acid is dissolved
• Measuring the volume of gas produced

  1. Pouring hydrochloric acid into a conical flask

  2. Adding magnesium

  3. Measuring the gas displaced in a measuring cylinder

  4. Measuring the gas collected in a gas syringe
• Using 2 mol per decimeter cubed hydrochloric acid


  Reaction has a faster rate
• Using 1 mol per decimeter cubed hydrochloric acid


  Reaction has a slower rate
• The results reach the same point because an excess of hydrochloric acid was used, so the magnesium was the limiting reactant
• Sources of error


  • Difficulty in starting the timer, adding the magnesium, and putting the bung in at the same time
  • Hydrogen may be lost at the start of the reaction
  • Measuring cylinder is imprecise, reading only to the nearest 1 cm3
• Using an inverted burette would provide greater precision, reading to 0.1 cm3