Chapter 14, Problem 1Q

Interpretation Introduction

Interpretation:

The reason for the broader melting point range observed for second sample should be determined.

Concept introduction:

For a crystalline substance, the temperature at which the substance changes from solid phase to liquid phase is referred to as melting point. Melting point is directly associated with the presence of intermolecular forces like hydrogen bonding, dipole-dipole interactions. High molecular symmetry, large surface area, polarity is related to high melting temperature.

A pure compound melt at a narrow range and compounds with impurities have broad melting temperature. Melting points are obtained by filling the organic compound into the capillary tube with one end sealed.

Explanation of Solution

To determine the melting point of a sample the capillary tube is filled with a sample with one end sealed. After that, the sample is heated to a temperature where the solid sample begins to convert into a liquid phase which signifies its melting point.

If too much sample is added to the capillary, the range of melting point becomes broad as more time it takes to melt the whole sample while the temperature of the sample increases with time.

Therefore the sample height of $\text{4-5}\text{mm}$ has a broader melting temperature range $\left(\text{141}\text{°C-145}°\text{C}\right)$ than for the sample height of $\text{1-2}\text{mm}$ with melting range of $\left(\text{141}\text{°C-142}°\text{C}\right)$ .