Experiment: Melting Point Analysis
OBJECTIVES
1. Determine melting point of a pure solid
2. Examine and account for the effect of molecular weight on melting point of organic compounds of
various carbon chain lengths
3. Identify an unknown solid using mixed melting point technique
4. Examine how the structural differences in fatty acids affect their physical properties and impact human
health
5. Perform experiment, collect, and analyze data. Record and report experimental work completely.
MATERIALS: Melting point apparatus, Melting point capillary tubes, Watch
glass
CHEMICALS: Lauric acid, Myristic acid, Palmitic acid, Stearic acid, Biphenyl,
Acetanilide, Fluorene
SAFETY
1. Students must wear personal protective equipment and comply with all safety and lab instructions
discussed in class.
2. Students must dispose all waste in a designated waste container.
Lab Overview
In this lab, you will determine melting point range of a pure solid and examine how to account for the effect of
molecular weight on melting point of organic compounds of various carbon chain lengths. Melting point is
defined as the temperature at which solid state of matter is in equilibrium with its liquid state. When a solid is
heated, the increase in temperature provides enough kinetic energy to solid-state particles to break existing
intermolecular forces and move more freely to convert to a liquid state. In a pure state, most organic
compounds exhibit narrow melting range (start and end melting between 1-2⁰C).
However, when a sample is impure, the impurity disrupts the crystalline structure of the solid, which lowers
and broadens the melting point range of the sample. This melting point depression can be used as a tool to
know the identity of an unknown pure solid. When a given unknown (pure solid) is mixed with guessed known
compound(s) the melting point of resulting mixture may or may not exhibit a melting point depression and
broadening. The observed melting point of the mixture can then be used to identify the unknown pure solid.
In this lab you will learn ‘mixed melting point’ technique to identify an unknown solid. Additionally, you will
learn how to make connections of studied concepts to real world examples by examining how the structural
differences in fatty acids affect their physical properties and impact human health.
1
, EXPERIMENTAL PROCEDURE
Read through the full procedure and answer pre-lab questions before coming to the lab.
Procedure A
Melting point of a pure known solid:
1. Packing of capillary tube: Examine the texture of given sample. If it is coarse, crush it to a fine powder
using mortar pestle. Obtain a capillary tube and press the open end of tube in a small heap of finely
powdered sample. Gently tap the capillary tube on the bench to pack the sample towards the closed end
of tube (2-3mm).
Figure 1: Packing of capillary tube
2. Place capillary tube in the melting point apparatus sample slot. Start heating the apparatus at a rate of
10⁰C per minute (fast run). Carefully watch the changing of sample appearance form solid to liquid phase
Record the temperature range when the sample starts to melt and finishes melting. Do not reuse the
capillary tube, discard it in a designated waste container.
Figure 2: Melting point apparatus
2
OBJECTIVES
1. Determine melting point of a pure solid
2. Examine and account for the effect of molecular weight on melting point of organic compounds of
various carbon chain lengths
3. Identify an unknown solid using mixed melting point technique
4. Examine how the structural differences in fatty acids affect their physical properties and impact human
health
5. Perform experiment, collect, and analyze data. Record and report experimental work completely.
MATERIALS: Melting point apparatus, Melting point capillary tubes, Watch
glass
CHEMICALS: Lauric acid, Myristic acid, Palmitic acid, Stearic acid, Biphenyl,
Acetanilide, Fluorene
SAFETY
1. Students must wear personal protective equipment and comply with all safety and lab instructions
discussed in class.
2. Students must dispose all waste in a designated waste container.
Lab Overview
In this lab, you will determine melting point range of a pure solid and examine how to account for the effect of
molecular weight on melting point of organic compounds of various carbon chain lengths. Melting point is
defined as the temperature at which solid state of matter is in equilibrium with its liquid state. When a solid is
heated, the increase in temperature provides enough kinetic energy to solid-state particles to break existing
intermolecular forces and move more freely to convert to a liquid state. In a pure state, most organic
compounds exhibit narrow melting range (start and end melting between 1-2⁰C).
However, when a sample is impure, the impurity disrupts the crystalline structure of the solid, which lowers
and broadens the melting point range of the sample. This melting point depression can be used as a tool to
know the identity of an unknown pure solid. When a given unknown (pure solid) is mixed with guessed known
compound(s) the melting point of resulting mixture may or may not exhibit a melting point depression and
broadening. The observed melting point of the mixture can then be used to identify the unknown pure solid.
In this lab you will learn ‘mixed melting point’ technique to identify an unknown solid. Additionally, you will
learn how to make connections of studied concepts to real world examples by examining how the structural
differences in fatty acids affect their physical properties and impact human health.
1
, EXPERIMENTAL PROCEDURE
Read through the full procedure and answer pre-lab questions before coming to the lab.
Procedure A
Melting point of a pure known solid:
1. Packing of capillary tube: Examine the texture of given sample. If it is coarse, crush it to a fine powder
using mortar pestle. Obtain a capillary tube and press the open end of tube in a small heap of finely
powdered sample. Gently tap the capillary tube on the bench to pack the sample towards the closed end
of tube (2-3mm).
Figure 1: Packing of capillary tube
2. Place capillary tube in the melting point apparatus sample slot. Start heating the apparatus at a rate of
10⁰C per minute (fast run). Carefully watch the changing of sample appearance form solid to liquid phase
Record the temperature range when the sample starts to melt and finishes melting. Do not reuse the
capillary tube, discard it in a designated waste container.
Figure 2: Melting point apparatus
2
