Lab 4 Melting Point Analysis

Purpose: 

To purify an impure compound and verify its identity (acetanilid or phenacetin) by melting point analysis

Recrystallization

a purification technique for impure solids that involves dissolving the solid in a minimal amount of hot solvent, then slowly cooling the solution to allow the pure compound to crystallize while impurities remain dissolved

Phenacetin Structure

Acetanilide Structure

Chemicals used

Phenacetin and Acetanilide

Melting point (MP)

The temperature where the solid and liquid phases of a substance are in equilibrium at a pressure of 1 atm

Melting point analysis is used

To check the purity of a compounds or to identify unknown compounds

When pure substances melt:

The solid and liquid phases of that substances are at equilibrium

When a substance is impure melts:

Its melting point broadens and is lowered slightly (freezing point depression)

Naphthalene structure

Biphenyl

Mixed melting point

technique which is used to determine the identity of unknown compounds

Items needed for this experiment:

Melting point apparatus aka Mel-temp, thermometer, and three melting point capillaries

Melt-temp Apparatus components

Thermometer port, eye port, dial control, capillary tube port, and on/off switch

A pure substance has

a single melting point

Good recrystallization solvent

High solubility in hot solvent and low solubility in cold solvents

Results

Unknown A is Phenacetin