Place 2 g benzophenone into a 20 mL vial and add about 10 mL 2-propanol. Dissolve the solid with gentle warming in a warm water bath. After the solid is dissolved, add 1 drop glacial (100%) acetic acid, then fill the vial with 2-propanol until it is a little more than half way into the screw neck of the vial. Tightly fasten the cap and invert the vial several times to mix the liquid. When the vial is inverted, if more than a small bubble of air is present, reopen the vial and add a little more 2-propanol.
Wrap the cap with a small strip of Parafilm to avoid any leakage, taking care not to wrap Parafilm around the main body of the vial. Put a strip of lab tape on the top of the vial with your name, the date, and the name of this laboratory. Place the vial in the windowsill in such as way that it will be exposed to as much light as possible.
Next week, harvest the product crystals which form by pouring off the liquid (organic waste container) and scraping the crystals from the vial with a spatula. After the crystals dry on an open watch glass, determine their mass and melting point.