AMOUNT OF SUBSTANCE

• The student rinses the burette with deionised water before filling with sodium hydroxide solution.

  State and explain the effect, if any, that this rinsing will have on the value and titre.

  Titre would increase

  NaOH would be more dilute
• The student noticed that some of the liquid injected into the gas syringe did not vaporise.

  Explain the effect that this has on the Mr calculated by the student.

  Increase the Mr

  Lower volume recorded
• PERCENTAGE YIELD?

  actual yield / theoretical yield x 100
• ATOM ECONOMY?

  mass of desired product / total mass of reactants
• State the importance of percentage yield and percentage atom economy when choosing the method used to make a compound.

  IMPORTANCE OF PERCENTAGE YIELD

  efficient conversion of reactants to products

  IMPORTANCE OF ATOM ECONOMY

  maximising mass of atoms that end up in desired products
• Define the term relative molecular mass (Mr).

  average mass of one molecule / 1/12 mass of 12C atom
• Some of the liquid injected did not evaporate because it dripped into the gas syringe nozzle outside the oven.

  Explain how this would affect the value of Mr of Y calculated from the experimental results.

  Increase Mr

  Lower volume recorded
• The student used a wash bottle containing deionised water when approaching the end-point to rinse the inside of the conical flask.

  Solution may be on the outside of flask too
• Suggest a reason, other than appartus inaccuracy, why the Mr value determined from experimental results differs from actual Mr.

  Explain your answer.

  Volume of gas in syringe is greater than true value (some leaked in)

  Therefore Mr is too small