Practical techniques and safety

Sample questions

Original practice questions written in the style of the exam.

1. Question 13 marks

   A student heats a mixture of butan-1-ol, sodium bromide and sulfuric acid under reflux.

   (a) Why are anti-bumping granules added to the flask?

   (b) Why must the top of the condenser not be stoppered?

   (c) Why does the cooling water enter the condenser at the bottom?

   Mark scheme

   • (a) To give smooth boiling / prevent large bubbles forming violently (1)
   • (b) Pressure would build up in the apparatus, which could explode (1)
   • (c) So that the condenser fills completely with water, giving more efficient cooling (1)
2. Question 24 marks

   A technician needs to make $250.0\,\text{cm}^3$ of a standard solution of sodium carbonate from the anhydrous solid.

   Describe how this should be done so that the concentration is known accurately.

   Mark scheme

   • Weigh the solid in a weighing bottle and record the mass transferred by difference (reweigh the bottle after emptying) (1)
   • Dissolve the solid in a small volume of distilled water in a beaker (1)
   • Transfer the solution to a $250\,\text{cm}^3$ volumetric flask, including all washings from the beaker and glass rod (1)
   • Make up to the mark with distilled water so the bottom of the meniscus is on the line at eye level, then stopper and invert several times to mix (1)