CP1 - Measuring the Molar Volume of a Gas

• Why is a weak acid used


  so that the reaction is slower so there's less gas lost between adding the marble chips and attaching the bung
• why can't you use too much calcium carbonate?


  so you don't produce more gas than the syringe Can hold
• how can you minimise gas loss

  wait until no effervescence is observed before weighing flask
• what's the equation for the reaction?

  CaCO3 + 2CH3 COOH →Ca(CH3COO)2 + CO2+ H20
• what chemicals are used?

  ethanoic acid

  calcium carbonate
• errors relating to the syringe


  plunger may not be free moving

  to reduce this use a lubricant
• errors to do with gas produced

  some gas escapes between addition of marble chips and sealing test tube - reduce this asing a test tube containing acid inside the vessel containing the marble chips & tip to mix reagent

  CO2 is slightly soluble in water so exactly volume isn't measured

  bung may not be airtight so some gas may escape
• errors regarding the solid


  some solid may be lost during transfers
• risk assessment


  ethanoic acid is irritant so can cause reddening of skin

  broken glass can cause cuts
• risk assessment - precautions


  ethanoic acid: wear goggles and lab coat, wash hands immediately if it comes into contact with skin

  broken glass: don't put glassware near the edge of the desk, don't touch broken glass
• what were the results like?


  the greater the mass of marble chips the higher the volume of carbon dioxide produced
• what does the graph of results look like?


  a straight line going through the origin