Question

5. What is the difference between the capillary melting point and true melting point?

Answer 1

What is Melting Point:-

Melting point of a compound is one way to test if the substance is pure. A pure substance generally has a melting range of one or two degrees. Impurities tend to depress and broaden the melting range so the purified sample should have a higher and smaller melting range than the original, impure sample.

Difference between capillary mealting point and true mealting point.

Capillary Melting Point:

Capillary Melting Point gives information about the melting range but it is different to assign an accurate melting point.

Thin-walled capillary melting point tubes are used to hold melting point samples. This tube needs to be sealed at one end

A packed capillary attached to a normal mercury thermometer

At the melting point it is necessary that the thermometer bulb and the sample in the capillary tube be at thermal equilibrium.

True Melting Point

True Melting point is exceedingly expensive and elaborate melting point apparatus is used, it is improper and incorrect to report a single temperature for a melting point.

Melting range data from previously melted samples is occasionally discouraged on grounds of possible sample decomposition or other physical or chemical change.

Samples often supercool as much as 30 oC below their melting points and our heating procedure usually begins at 40°C below the approximately known value of the melting point.

Clear point temperature data that we obtained from a sample of the phenacetin melting point reference standard Plots of these data versus the square root of the ramp rate. These relationships indicated a true melting point.