Melting Point Determination | Organic Chemistry Lab

Learn that melting point is a physical property used to identify unknown solids and assess purity. Pure solids have sharp melting points while impure solids melt over a wider temperature range and at lower temperatures than literature values.

Identify melting point tubes as capillary tubes sealed on one end. Understand that the solid sample must be packed tightly at the closed end at a height of 1 to 3 millimeters for proper analysis.

Grind a representative portion of the solid sample into a fine powder. Scoop small amounts of powder into the open end of the melting point tube and tap it on the counter to move the sample down to the sealed end until achieving 1-3 mm of tightly packed material.

Review the components of the apparatus: heating block, sample slot, thermometer, power switch with integrated light, magnifying glass window, and temperature control dial. Understand that slow heating is essential to avoid heat lag and allow accurate temperature recording.

Have pen and notebook ready to record data live during the experiment. Understand that you will be observing two key temperatures: the first sign of melting and the complete disappearance of all crystals.

Watch the crystals through the magnifying window as the sample heats slowly. Record the temperature when crystals first appear wet (first melting), then continue watching until the last crystal disappears and only liquid remains (final melting temperature).

Report the melting point as a range with two temperatures (even if identical). A sharp 1-2 degree range indicates high purity, while a wider range and lower temperature than literature values indicate the presence of organic impurities.