Determination of an Unknown Liquid and an Unknown Solid by the Measurements of Physical Properties

Determination of an Unknown Liquid and an Unknown Solid by the Measurements of Physical Properties

Nicole Schmitt

Chem 261.005

02-06-2013

Introduction

All substances possess a unique set of physical and chemical properties that allow for the differentiation of one from another. Physical properties are those that a substance exhibits without any change in its composition; whereas chemical properties are displayed when a chemical change has occurred and the composition has been altered (it is therefore no longer the same substance). It is, therefore, the physical properties of a substance that enable us to discern one substance from another when the identity is unknown. Extensive physical properties, such as mass and volume, are dependent upon the amount of substance present and are therefore not useful when determining the identity of an unknown substance.

To begin the experiment, two conceptual analyses were completed: the first to demonstrate the relationship of mass and volume to density, and the second to illustrate the relationship between temperature and the intensive physical properties of density and solubility. In the last two steps, the intensive physical properties displayed by an unknown solid and an unknown liquid were analyzed in order to determine the identities of each. The melting point and solubility in both distilled water and cyclohexane were observed in the unknown solid “#9”; the density, boiling point, and solubility in both distilled water and cyclohexane were obtained for the unknown liquid “H”.

The density of a substance is a ratio of its mass to its volume, and is displayed as

Density = mass/volume

Density is typically unique to each substance, and is therefore a useful tool in the determination of the identity of an unknown substance. Although both mass and volume are extensive properties, the density of a particular substance remains the same regardless of the amount present at any given time. For most...