Question

During a melting point determination, it is normal to first take a rapid rough measurement followed by a slower more accurate measurement. why is it important to allow the mel-temp to cool 15 °c before placing the second capillary tube in, and to set the voltage generate 1–2 °c temperature increase per minute?

Answer 1

The right answer is A rapid temperature increase will give a melting point range that is too high.

The melting point is determined in a capillary tube. it means the temperature at which the substance is completely melted, indicated by the disappearance of the solid, will not differ by ± 4 ° C from the given value, unless otherwise indicated.

The following technique can be applied to determine the melting point:

Grind some amount of substance in a small mortar. Place in a vacuum desiccator containing silica gel or phosphorus pentoxide and allow to dry for 24 hours at room temperature (unless another method of drying is indicated in the test protocol) . Introduce the substance into a dry capillary tube 1 mm inside diameter to form a column about 3 mm high. Heat the melting device to a temperature 5 to 10 ° C below the expected melting temperature and adjust the heating so that the temperature of the enclosure rises by approximately 1 ° C per minute. Introduce the capillary tube containing the substance into the heated chamber and note the temperature at which the agglomerated substance becomes completely transparent; this temperature constitutes the melting point.