Experiment 2 - Physical Properties

Objectives

1. to determine the density of water, ethanol and hexane
2. to determine the melting point of an unknown compound and then use this melting point as an aid in its identification. The unknown compound will be one of the following:
   • Acetanilide (m.p. = 113 -115^oC)
   • Benzoic acid (m.p. = 122^oC)
   • Cinnamic acid (m.p. = 133^oC)
   • Adipic acid (m.p. = 152^oC)
   • Salicylic acid (m.p. = 159^oC)
3. to compare the solubility of various solid substances in water and in hexane. Various liquids will also be mixed to determine which combinations are miscible and immiscible.

Introduction

Density is a physical property which can be used to identify substances. Density is defined as the mass per unit of volume

Density = mass/volume

Mass is a measure of the quantity of matter contained in an object. Volume is a measure of the space occupied by an object.

The melting point and boiling point of a substance are also characteristic physical properties, which can be used to identify a substance. The melting point is defined as the temperature at which the liquid and solid phase of a substance co-exist at equilibrium. Pure compounds melt at a sharp temperature. Impure compounds melt at a lower temperature and over a wider temperature range. The boiling point of a substance depends on the air pressure. The greater the air pressure the higher the boiling point.

A solution has two components, a solute and solvent. When sugar dissolves in water the sugar is the solute and the water is the solvent. Whether a solute dissolves in a solvent to form a solution depends on the nature of the solute and solvent. Substances which dissolve in water (e.g. sugar) are described as being soluble while other substances (e.g. sand), which do not dissolve in water are described as insoluble.

If two liquids are soluble in each other (e.g. alcohol and water) they are described as being miscible. Two liquids, which are insoluble in each other (e.g. oil and water) are said to be immiscible.