SECOND LECTURESECOND LECTURE

Systems containing two liquid Systems containing two liquid components.components.

Two Component Systems Containing Liquid Phases:

miscible partially miscible immiscible

ethyl alcohol and water water and mercuryphenol and water

Phenol and water system:

miscible Partially miscible

Two factors affecting misciblity

1 -Concentration of phenol in water. 2- Temperature.

Two component systemsTwo component systems::

Phenol

Phenol / water

water

The curve g b h c i shows limits of temperature and concentration within which two liquid phases exist in

equilibrium.

1 phase

10 % phenol 11 % phenol 24% phenol

> 63 % phenol 1 phase

Point A100% water

2 phases

water rich phasecontains water+ phenol(11%)

Phenol rich phasecontains Phenol (63%)+ water

PhenolPhenol

Point A100% water (pure water)

Point B (11 % phenol)2 phases

water rich phase& phenol rich phase

More PhenolMore Phenol

Point C ( >63% phenol) 1 phase

Completely miscible

The curve g b h c i shows limits of temperature & concentration within which two liquid phases exist in equilibrium.

The Tie LineThe Tie Line

It is always parallel to the base line It is always parallel to the base line in two component systemsin two component systems . .

All systems prepared on a tie lineAll systems prepared on a tie line,, at equilibrium, will separate into at equilibrium, will separate into

phases of constant phases of constant composition. known as composition. known as conjugate phasesconjugate phases . .

Any system represented by a point Any system represented by a point on the line bc , at 50on the line bc , at 50ooC. C. separates to give a pair of separates to give a pair of conjugate phases whose conjugate phases whose composition is composition is 11% phenol11% phenol

in water rich phase (A) & in water rich phase (A) & 63 % 63 % phenolphenol in phenol rich phase in phenol rich phase..

Importance of Tie lineImportance of Tie line::

Calculation of the composition of Calculation of the composition of each phase. each phase.

Determination of the weight of each Determination of the weight of each phases. (calculation of the phases. (calculation of the distribution of phenol (or water) distribution of phenol (or water) throughout the system as a whole. throughout the system as a whole.

F= 2 - 2 +1F= 2 - 2 +1

22

F = 2 - 1 +1F = 2 - 1 +1

11

The use of Tie line in calculationsThe use of Tie line in calculations::

As an example, let us suppose that we mixed 24 g As an example, let us suppose that we mixed 24 g of phenol with 76 g of water, warmed the mixture of phenol with 76 g of water, warmed the mixture to 50to 50ooC, and allowed it to reach equilibrium at this C, and allowed it to reach equilibrium at this temperature.temperature.

Weight phase A/weight of phase B = dc/bd =63-Weight phase A/weight of phase B = dc/bd =63-24/24 -11=39/13 =3/124/24 -11=39/13 =3/1

Weight of A= Weight of A= ¾¾ x 100= 75, wt. of B = x 100= 75, wt. of B = ¼¼ x 100= x 100= 2525

Phase A=75 gm , phase B =25 gm.Phase A=75 gm , phase B =25 gm. Amount of phenol in A=75 x 11/100= 8.25 gmAmount of phenol in A=75 x 11/100= 8.25 gm Amount of phenol in B= 25 x 63/100= 15.75 gmAmount of phenol in B= 25 x 63/100= 15.75 gm

24 gm24 gm

Application of Tie lineApplication of Tie line::

To formulate systems containing more To formulate systems containing more than one component where it may be than one component where it may be advantageous to achieve a single-phase advantageous to achieve a single-phase product. product.

Handling of solid phenol, a necrotic agent Handling of solid phenol, a necrotic agent (caustic agent), is facilitated in the (caustic agent), is facilitated in the pharmacy if a solution of phenol and water pharmacy if a solution of phenol and water is used. The most convenient formulation is used. The most convenient formulation of a single liquid phase solution was 80% of a single liquid phase solution was 80% w /v, equivalent to about 76% w / w. This w /v, equivalent to about 76% w / w. This mixture has a freezing point of about 3.5mixture has a freezing point of about 3.5ooC C

The Critical Solution Temperature: The Critical Solution Temperature: CSTCST Is the maximum temperature at which the Is the maximum temperature at which the

2-phase region exists (or upper consolute 2-phase region exists (or upper consolute temperature). In the case of the phenol-temperature). In the case of the phenol-water system, this is 66.8water system, this is 66.8ooC (point h)C (point h)

All combinations of phenol and water > All combinations of phenol and water > CST are completely miscible and yield 1-CST are completely miscible and yield 1-phase liquid systems.phase liquid systems.

Systems Showing a Decrease in Systems Showing a Decrease in Miscibility with Rise in Miscibility with Rise in TemperatureTemperature::

A few mixtures, exhibit a lower A few mixtures, exhibit a lower critical solution temperature critical solution temperature (low CST), e.g. triethylamine (low CST), e.g. triethylamine plus water. The miscibility plus water. The miscibility with in temperature. with in temperature.

In the preparation of paraldehyde In the preparation of paraldehyde enemas, (consist of a solution of enemas, (consist of a solution of paraldehyde in normal saline). paraldehyde in normal saline).

Cooling the mixture during Cooling the mixture during preparation allows more rapid preparation allows more rapid solution, and storage of enema in solution, and storage of enema in a cool place is recommended. a cool place is recommended.

Systems Showing Upper and Systems Showing Upper and Lower CSTsLower CSTsThe 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.

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.

Type of CST

Solubility of additive in each

component

Effect on

CST

Effect on miscibil

ity

UpperApprox. equally

soluble in both components

Lowered

Increased

UpperReadily soluble in one

component but not in the other

RaisedDecreased

LowerApprox. equally

soluble in both components

RaisedIncreased

LowerReadily soluble in one

component but not in the other

Lowered

Decreased

The Effects of Added Substances on CST:

Addition of substanceAddition of substance That equally miscibleThat equally miscible

In 2 phasesIn 2 phases..