How is a solid sample prepared for melting point measurement using a capillary tube?

A) The sample is melted first and then poured into the capillary tube to solidify.

B) The sample is placed in the capillary tube without grinding or packing.

C) The sample is ground into a fine powder, placed into the capillary tube, and packed by tapping it against a surface.

D) The sample is dissolved in a solvent before being introduced into the capillary tube.

Grind the Sample: The solid sample should first be ground into a fine powder. This ensures uniformity and increases the surface area, which allows for an accurate melting point measurement.
Fill the Capillary Tube: The ground sample is then introduced into a melting point capillary tube. This tube is a thin glass tube sealed at one end.
Pack the Sample: Once the powdered sample is inside the tube, it needs to be packed tightly. This is usually done by repeatedly tapping the sealed end of the capillary tube gently on a hard surface. This helps the sample settle at the bottom of the tube, ensuring there are no air gaps that could affect the measurement.

These steps prepare the sample effectively for an accurate melting point determination. Therefore, the correct answer is C) The sample is ground into a fine powder, placed into the capillary tube, and packed by tapping it against a surface.

Melting point determination is a critical process in chemistry used to characterize the purity and identity of a solid compound. Impurities typically lower the melting point and broaden the melting range.