Three – Component System

JANUEL ZOE M. PAÑARES

Department of Chemical Engineering, College of Engineering and Architecture

Cebu Institute of Technology – University

N. Bacalso Ave. Cebu City, 6000 Philippines

The purpose of this experiment is to determine the solubility limits in a system made

up of water and two other liquids, one or both of which are only partially miscible with water

and to plot the solubility curve of the given three-component system. Eight 20-gram solutions

containing 10 %, 25 %, 40 %, and 60 % by weight of acetic acid in water and acetic acid in

benzene were prepared at a constant temperature of 25 °C, The solutions were titrated to

cloudiness with benzene and with water, respectively. The percent composition of each

component was computed and plotted on a ternary diagram.

1. Introduction

A phase diagram shows the phases existing in equilibrium at any given condition.

According to the phase rule, a maximum of four intensive variables (intensive properties)

must be specified to completely define the state of a three-component system. The intensive

variables that are usually chosen are pressure, temperature, and concentration.

For a three-component system at constant pressure and temperature, the solubility

relations of the system can be represented using an equilateral triangle. The percentage of

each component is represented by the perpendicular distance from the side opposite one apex

to any point on the diagram, and each pure component is represented by each vertex of the

triangle.

2. Materials and Methods

2.1 Materials and Apparatus

The materials used in this experiment are component A (water), 75 ml of

component B (Acetic acid), and 100 ml of component C (benzene). The apparatus

used are the thermometer, 2 burettes, 8 glass-stoppered bottles (50 ml). 1 5-ml pipette.

2.2 Methods

Solutions of known concentrations were prepared containing 10%, 25%, 40%,

and 60% by weight of acetic acid in water. Twenty grams of each solution was

prepared and placed in a 50-mL glass-stoppered bottle. A constant temperature of 25

°C was set and the solution was titrated with the third component, benzene. The

solution was shaken vigorously after each addition of the titrant. The end point of the

titration was taken to be the first appearance of perceptible cloudiness. Solutions

containing 10%, 25%, 40%, and 60% by weight of acetic acid in benzene were

prepared. The solutions were titrated to cloudiness with water at a constant

temperature of 25 °C.

The percent by weight of each component present at the appearance of the

second phase was calculated and plotted on a ternary diagram. A smooth curve was

drawn through the points.

On the diagram, a point designated as M lying in the heterogeneous region about

midway between the center of the region and one side of the bounding curve was

selected. A 50-mL sample, with a composition corresponding to the selected point on

the diagram, was prepared and shaken vigorously for several minutes. The sample

was then allowed to stand until two separate layers were formed. With the aid of a

separatory funnel, each layer was run into a weighted flask. The weight of each

solution was determined to the nearest twentieth of a gram. One ml of water was

added to each sample to determine the water-rich phase. The water-rich solution was

to remain homogeneous after the addition of water and the other is to become

heterogeneous after the addition of water.

3. Results