1. Systems containing two liquid components.
SECOND LECTURE
Systems containing two liquid components.

2. Two Component Systems Containing Liquid Phases:
miscible
partially miscible
immiscible
ethyl alcohol and water
phenol and water
water and mercury
Phenol and water system:
Two factors affecting misciblity
1- Concentration of
phenol in water.
2- Temperature.
miscible
Partially miscible

3. Two component systems:
Phenol
Phenol / water
water

4. The curve g b h c i shows limits of temperature and concentration within which two liquid phases exist in equilibrium.
2 phases
1 phase
11 % phenol
Point A
100% water
10 % phenol
24% phenol
water rich phase
contains water+ phenol(11%)
> 63 % phenol
1 phase
Phenol rich phase
contains Phenol (63%)+ water

5. water rich phase& phenol rich phase
The curve g b h c i shows limits of temperature & concentration within which two liquid phases exist in equilibrium.
Point A
100% water (pure water)
Phenol
Point B (11 % phenol)
2 phases
water rich phase& phenol rich phase
More Phenol
Point C ( >63% phenol)
1 phase
Completely miscible

6. The Tie Line
It is always parallel to the base line in two component systems.
All systems prepared on a tie line,
at equilibrium, will separate into phases of constant composition. known as conjugate phases.
Any system represented by a point on the line bc , at 50oC. separates to give a pair of conjugate phases whose composition is 11% phenol
in water rich phase (A) & 63 % phenol in phenol rich phase.

7. Importance of Tie line:
Calculation of the composition of each phase.
Determination of the weight of each phases. (calculation of the distribution of phenol (or water) throughout the system as a whole.

8. F = 2 F= 1

9. The use of Tie line in calculations:
As an example, let us suppose that we mixed 24 g of phenol with 76 g of water, warmed the mixture to 50oC, and allowed it to reach equilibrium at this temperature.
Weight phase A/weight of phase B = dc/bd =63-24/24 -11=39/13 =3/1
Weight of A= ¾ x 100= 75, wt. of B = ¼ x 100= 25
Phase A=75 gm , phase B =25 gm.
Amount of phenol in A=75 x 11/100= gm
Amount of phenol in B= 25 x 63/100= gm gm

10. Application of Tie line:
To formulate systems containing more than one component where it may be advantageous to achieve a single-phase product.
Handling of solid phenol, a necrotic agent (caustic agent), is facilitated in the pharmacy if a solution of phenol and water is used. The most convenient formulation of a single liquid phase solution was 80% w /v, equivalent to about 76% w / w. This mixture has a freezing point of about 3.5oC

11. The Critical Solution Temperature: CST
Is the maximum temperature at which the 2-phase region exists (or upper consolute temperature). In the case of the phenol-water system, this is 66.8oC (point h)
All combinations of phenol and water > CST are completely miscible and yield 1-phase liquid systems.

12. Systems Showing a Decrease in Miscibility with Rise in Temperature:
A few mixtures, exhibit a lower critical solution temperature (low CST), e.g. triethylamine plus water. The miscibility with in temperature.
In the preparation of paraldehyde enemas, (consist of a solution of paraldehyde in normal saline).
Cooling the mixture during preparation allows more rapid solution, and storage of enema in a cool place is recommended.

13. Systems Showing Upper and Lower CSTs
The miscibility with temp. in systems having a lower CST is not indefinite.
> a certain temperature miscibility starts to again with further in temperature.
Closed-phase diagram, i.e. nicotine-water system.

14. Blending :
The in miscibility of two liquids due to the addition of a third substance.
Example : the formulation of solution of cresol with soap BP 1968, which contains 50% cresol.
Cresol is only partially miscible with water, but the soap in this preparation decreases the upper CST and produces complete miscibility at ordinary temperature.

15. Solubility of additive in each component
The Effects of Added Substances on CST:
Effect on miscibility
Effect on CST
Solubility of additive in each component
Type of CST
Increased
Lowered
Approx. equally soluble in both components
Upper
Decreased
Raised
Readily soluble in one component but not in the other
Lower

16. Addition of substance
That equally miscible
In 2 phases.