Phase Rule in three component system

Deepak Gahlot

1. Samrat Prithviraj Chauhan Government College,Ajmer Seminar Project Department of Chemistry Submitted by – Deepak Gahlot Class – M.Sc. Semester I Topic : Application of phase rule to three component system – acetic acid + chloroform + water. 2021-2022

2. Basics. Phase rule. Three component system. Graphical representation of ternary system. Water-acetic acid-chloroform system. Conclusion. Reference. CONTENT

3. Homogeneous solution : A homogeneous solution means a solution which is of uniform (similar) composition. For example – 1 spoon sugar mixed in 1 glass of water. Heterogeneous solution : A heterogeneous solution is one which is of distinct composition (looks different).For example – sand and water solution. Miscible liquid : Miscible liquids are those which will completely dissolve/mix in each other. For example – lemonade. Partially miscible liquids : Partially miscible liquids are those liquids which will not completely dissolve or mix but some amount of them will. For example – 1-Butanol and water. Basic terminology

4. Immiscible liquids : Immiscible liquids are those which will not mix at all and will remain in separate layers. For example - oil and water. Phase : homogeneous, physically distinct, mechanically separable part of a system and is in dynamic equilibrium with each other. For example – oil, water and sugar solution. Component : It means the minimum number of constituents sufficient for determining the composition of all phases of a system. For example – ice,water and water vapour exists in 3 phases but their constituent element is same (H 2 O),hence 1 component system. Degree of freedom : It is the minimum no. of independent variables such as temperature,pressure and concentration that must be ascertained so that a given system in equilibrium is completely defined.For example: water and water vapour is a 2 phase system having DOF 1 since at 100 ° C,pressure is 1 atm.

5. The phase rule was discovered by “Josiah Willard Gibbs” in 1875 and is known as Gibbs phase rule.It states that in a heterogeneous system in equilibrium,the sum of no. of phases and number of degrees of freedom is equal to the number of components plus two.Mathematically,it is expressed as – where P = number of phases F = number of degree of freedom C = number of components 2 = additional variable of temperature and pressure Phase rule P + F = C + 2

6. For three component system,phase rule equation becomes If we consider minimum no. of phases (P=1),then to represent three component system , 4 DOF i.e; 4 variables viz. pressure,temperature,and composition of two components will be required. Graphical representation with 4 variables is not possible,so 2 variables pressure and temperature are kept constant.Hence reduced phase rule for 3 component system is Three component system F = C - P + 2 = 3 - P + 2 = 5 - P F = 3 - P

7. The popular method of representing a ternary system was given by Stokes & Roozeboom and is called as triangular plot. In this method , variation of compositions of three components at constant pressure and temperature are expressed by means of equilateral triangle.Each apex of the triangle is taken as 100 % (weight or mole)of the component with which it is designated. Each side of the triangle is divided into 10 equal parts and then lines parallel to three sides are drawn.Any point on any side of the triangle refers to composition of 2 components in the system. While any point in the triangle represents compositions of all the 3 components. Graphical representation of ternary system

8. Fig. – Graphical representation of a three component system

9. This 3 component liquid system is a type of one pair of partially miscible liquids.Of the three components H 2 O,CHCl 3 & CH 3 COOH the acetic acid is completely miscible with water and chloroform separately but water and chloroform are only partially miscible between themselves. H 2 O & CHCl 3 being partially miscible forms layers each saturated with other component.The mixture will form two conjugate solutions given by the points b and c as shown in the graph. Water + chloroform + acetic acid system

10. When CH 3 COOH is added to this solution,the miscibility of H 2 O & CHCl 3 is enhanced.’A’ will distribute itself between the two layers and the layers become conjugate ternary solutions.The composition of these two solutions are given by the points b’ and c’.The solution is still heterogeneous. As more and more CH 3 COOH is added, then the two layers emerge into a clear solution forming only one layer containing all the three liquids. The points come more closer till it merges to a point K. The composition of two layers at this point is same and this K point is called as the plait point or isothermal critical point.

11. Any solution outside the curve XKY will be homogeneous and inside it will be heterogeneous. This curve is known as binodal curve .The points joined together form parallel lines and are called as tie lines. These tie lines are parallel because the added constituent ( acetic acid ) distributes itself equally in both the layers of water and chloroform. Thus, they are horizontal tie lines in this case. The tie line will not be parallel always but in slope form if the added component dissolves more in one than the other.

12. Fig. – Three liquids with one partially miscible pair.

13. Ternary phase diagram construction is the best approach to study all the types of formulations by mixing of water, oil and and surfactant.It provides the scientific basis for the screening of different formulation components and determination of optimum conditions for existence of equilibrium. It is widely used in research and formulation studies of various pharmaceutical formulations and process. Spectrometric study of Au,Ag and Cu to find the impurity we use this 3 component phase rule application. Conclusion

14. Advanced physical chemistry by D.N.Bajpai (S.Chand), page no. 393… Advanced physical chemistry by Gurtu & Gurtu (Pragati Prakashan),page no. 240… Advanced Physical Chemistry by Puri Sharma Pathania, page number 692… Reference

15. Thank you