CHEM 40.1 EXER 3 SIMPLE

SIMPLE DISTILLATION

Sample appears to be HOMOGENOUS and can be a:

1.    Solution of a nonvolatile solute in a volatile solvent

2.    Solution of two miscible liquids with one being more volatile than the other

HOMOGENOUS MIXTURES:

-       Has uniform composition through out the mixture and the components cannot be separated by physical means

For example: the one we used in the exercise is a mixture of water and ethanol, they are homogenous upon looking at the mixture we cannot distinguish which one is ethanol or water

MAIN PRINCIPLES:

-       Involves evaporation of the samples and allows separation based on the differences in the boiling points of the components

-       Employs the raoult’s law which states that the vapor pressure of a compound is lowered when it becomes part of a solution. The resulting vapor pressure of the compound is a function of its molar composition in the solution. This is shown in the equation below:

Where:

PA – vapor pressure of the compound A when in solution

 – vapor pressure of the compound A when present in pure form

 – mole fraction of A in the mixture

TEMPERATURE AT WHICH THE MIXTURE BOILS:

Mixture starts boiling upon reaching the boiling point of the desired substance

Example: A water-ethanol mixture will boil when the boiling point of the more volatile component – methanol is reached thus the mixture will boil at around 78-79 degrees celcius.

CONTENTS OF DISTILLATE:

The distillate obtained from the simple distillation SHOULD CONTAIN THE DESIRED SUBSTANCE needed to be separated from the rest of the mixture

Example: in water-ethanol mixture the distillate should only contain ethanol. Ethanol is the substance of interest and which is the more volatile component and which has the lower boiling point.

APPLICATION:

Separating substances with wide differences in boiling points.

LIMITATIONS:

1.    Cannot be used to separate mixtures with components that have close boiling points

2.    Cannot be used for compounds that decompose at their boiling point

SETUP:

1.    We used a thermometer and is used to monitor the temperature of the distillation.

a.    When the mixture begins to boil, the first temperature reached is the boiling point of the more volatile component.

b.    The temperature reading at boiling can be provide means to identify the distillate since this temperature reading is the point that may provide the identity of the unknown distillate

2.    Glassware used to receive the distillate is usually a beaker, Erlenmeyer flask or when the volume is required to be accurately measured, a graduated cylinder