Solution:
i. Apparatus required:
- Cold finger
- Hot plat & heat dissipation block
- Suction flask
- Miniature water pump
- Spatula
ii. Procedural flow diagram:
- Place a known quantity, accurately
weighed, of benzoic acid in the suction flask placed in a well with
a window for observation in a heat dissipation block..
- Assemble the cold finger with the
flask. Connect it to a miniature water pump with water hoses.
Note: Ice can be added to the water container to
obtain much cooler water for circulating in the cold finger.
- Turn on the heat.
- Keep the heat stable at 150 -
155oC. Note: The pure benzoic acid
sublimes, crystals form on the cold finger.
- Continue heating until no more
crystals form on the cold finger.
- Turn off the heat.
- Remove the apparatus from the heat,
allow it to cool at room temperature.
- Carefully, dissemble the cold
finger from the suction flask.
- Scarp the crystals onto a tared
piece of weighing paper and reweigh.
- Record the mass of pure benzoic
acid.
- Calculate the percent recovery
using the below formula. % recovery = (Mass recovered / Input mass)
x 100%
- Measure the melting point the pure
benzoic acid to identify its purity.