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Solubility and Partition Phenomena. Contents  General Principles  Solvent-Solute Interactions  Solubility of Gases in Liquids  Solubility.

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Presentation on theme: "Solubility and Partition Phenomena. Contents  General Principles  Solvent-Solute Interactions  Solubility of Gases in Liquids  Solubility."— Presentation transcript:

1 Solubility and Partition Phenomena

2 Contents  General Principles  Solvent-Solute Interactions  Solubility of Gases in Liquids  Solubility of Liquids in Liquids  Solubility of Solids in Liquids  Partition Phenomena

3 Ⅰ. General Principles  Definitions  Solubility Expressions  Factors Affecting Solubility

4 Definitions  Solution : a liquid in which a solid substance has been dissolved. Solute : a solid substance that is dissolved in a liquid. Solvent : a liquid that can dissolve other substances.  Solubility : the concentration of solute in a saturated solution at equilibrium at a given temperature given as per weight or volume of solvent g (solute) / 100g (solvent) 1g (solute) / volume (ml) of solvent

5  Saturated Solution the solute is in equilibrium with the solid phase  Unsaturated or Subsaturated Solution one containing the dissolved solute in a concentration that necessary for complete saturation at a definite temperature  Supersaturated Solution one that contains more of the dissolved solute than it would normally contain at a definite temperature

6  Miscible the solute when it is a liquid and will form a solution with a solvent over any concentration range  The Phase Rule F = C – P + 2

7 Solubility Expressions USP Chart of Descriptive terms TermParts solvent to 1 part solute Very solubleLess than 1 Freely soluble1-10 (3-10%) Soluble10-30 Sparingly soluble Slightly soluble Very slightly soluble ,000 Practically insoluble, insoluble More than 10,000 용어 썩 잘 녹는다 잘 녹는다 녹는다 조금 녹는다 녹이 어렵다 매우 녹기 어렵다 거의 녹지 않는다 대한약전 제 8 개정

8 Factors Affecting Solubility  Temperature  Pressure C 2 = σp  pH  Chemical Structures - Dipole moment - Dielectric properties - Hydrogen bonding

9 Ⅱ. Solvent – Solute Interactions 1.Polar Solvents 2.Nonpolar Solvents 3.Semipolar Solvents “Like Dissolves Like”

10 Polar Solvents  Influential Factors Dipole moment Hydrogen bonds Acidic and basic character of constituents Structural features  Mechanism High dielectric constant Amphiprotic Dipole interaction force  Water (dissolve ionic solutes and other polar substances)

11 Non-polar Solvents  Influential Factors Induced dipole interactions Weak van der Waals-London type forces  Hydrocarbons (dissolve nonpolar solutes)

12 Semi-polar Solvents  Influential Factors Induce a certain degree of polarity in non-polar solvent molecules  Ketones and alcohols (Intermediate solvents)

13 Ⅲ. Solubility of Gases in Liquids 1.Effect of Pressure 2.Effect of Temperature 3.Salting Out 4.Effect of Chemical Reaction 5.Solubility Calculations

14 Effect of Pressure  Henry’s Law C 2 = σp C 2 = concentration of the dissolve gas (g/l) p = partial pressure (mm of the undissolve gas) σ = inverse of the Henry’s law constant, K in a dilute solution at constant temperature, the concentration of dissolved gas is proportional to the partial pressure of the gas above the solution at equilibrium

15 Effect of Temperature  As the temperature increases, the solubility of most gases decreases, owing to the greater tendency of the gas to expand

16 Salting Out  Gases are often liberated from solutions in which they are dissolved by the introduction of an electrolytes and sometimes by a nonelectrolyte NaCl sucrose gases carbonated solution

17 Effect of Chemical Reaction  Gases (HCl, NH3, CO2) + Solvent → Chemical reaction → Increase solubility

18 Solubility Calculations  Inverse Henry’s law constant,  C 2 =  P  Bunsen absorption coefficient,   : 일정 온도, gas 의 partial pressure 1 기압하에 solvent 1L 에 녹 는 gas 의 volume (L) Satuated condition : 0 ℃, 760mmHg V gas. STP V soln. =  P

19 Ⅳ Solubility of Liquids in Liquids 1.Ideal and Real Solutions 2.Complete Miscibility vs Partial Miscibility 3.Influence of Foreign Substances 4.Influence of Solvents on Solubility

20 Ideal and Real Solutions  Ideal Solutions Raoult’s Law:  Nonideal Solutions a. Negative deviation b. Positive deviation

21 Raoult’s Law  Negative deviation Associated with hydrogen bonding between polar comp AAAB Increased solubility Chloroform & acetone

22  Positive deviation Cannot mingle with each other Partial solubility Decreased solubility BA AA Raoult’s Law

23 Miscibility  Complete Miscibility Solvents are said to be completely miscible when they are mix in all proportions  Partial Miscibility When certain amounts of two liquids are mixed, two liquid layers are formed, each containing some of the other liquid in the dissolved state

24 Miscibility

25 Influence of Foreign Substances  If the added material is soluble in only one of the two components / if the solubilities in the two liquids are markedly different mutual solubility of the liquid pair is decreased  When the third substance is soluble in both of the liquids roughly the same extent the mutual solubility of the liquid pair is increased  Blending : the increase in mutual solubility of two partially miscible solvents by another agent  Micellar Solubilization : solubility in water of a non-polar liquid is increased by a micelle-forming surface-active agent Binary addition Ternary

26 Ⅴ Solubility of Solids in Liquids 1.Ideal Solutions 2.Nonideal Solutions 3.Solvation and Association in Solutions of Polar Compounds 4.Solubility and the Heat of Solution 5.Solubility of Strong Electrolytes 6.Solubility of Slightly Soluble Electrolytes 7.Solubility of Weak Acids and Weak Bases in Water as Influenced by pH 8.The Influence of Solvents on the Solubility of Drugs

27 Ideal Solutions T = absolute temp. of the solution T 0 = melting point of the solid solute X 2 i = ideal solubility of the solute expressed in mole fraction ∆H f = Heat of solutions → Heat of fusion Heat of solution = Heat of fusion Not affected by the nature of the solvent No longer applies when T > T 0 and at temperatures considerably below the melting point Depends on temperature, melting point of the solid, and molar heat of fusion

28 Nonideal Solutions T = absolute temp. of the solution T0 = melting point of the solid solute ∆Hf = Heat of solutions → Heat of fusion γ2 = the mole fraction scale is known as the rational activity coefficient log γ2 : intermolecular forces of attraction in removing a molecule from the solute phase and depositing it in the solvent

29 (a) (c) (b) solute solvent solution Liberation of a molecule from the solute Creation of a hole in the solvent solute molecule W 22 W 11 -2W 12 Total work : (W 22 + W 11 -2W 12 )

30  Solubility Parameter ΔH v = the heat of vaporization V l = the molar volume of the liquid at the desired temperature

31 Solvation and Association in Solutions of Polar Compounds  Solvation - 2w 12 > w 11 + w 22 - = negative - negative deviation from Raoult’s law  Association - interaction occurs between like molecules of one of the components in a solution - = positive - positive deviation from Raoult’s law

32 Solubility and the Heat of Solution  ∆H soln : heat of solution

33 Solubility of Strong Electrolytes  Endothermic process (absorbs heat) a rise in temperature increases the solubility of a solid  Exothermic process (heat is evolved) the solubility decreases with an elevation of the temperature

34 Solubility of Slightly Soluble Electrolytes  Solubility product, : the real solution solubility of poorly soluble strong electrolytes in water is calculated by using the solubility product constant obtained from thermodynamics  Common ion : adding a common ion is to reduce the solubility of a slightly soluble electrolyte

35 Solubility of Weak Acids and Weak Bases in Water as Influenced by pH  Weak Acids  Weak Bases

36 The Influence of Solvents on the Solubility of Drugs  Strong Electrolytes : strong acids and bases and all salts are soluble in water  Weak Electrolytes : weak acids and bases with high molecular weight are not soluble in water  Nonelectrolytes : high-molecular-weight organic drugs that do not dissociate or associate in water are generally soluble in organic solvents and have little or no solubility in water  Cosolvency : a solute is more soluble in a mixture of solvents than in one solvent alone

37 Cosolvency The solubility of phenobarbital in a mixture of water, alcohol, and glycerin at 25 ℃

38 Ⅵ. Partition Phenomena 1.General Partitioning Concepts 2.For Strong Electrolytes as Solutes 3.For Nonelectrolyte Solutes 4.For Weak Electrolytes as Solutes 5.Application of Distribution Concepts 6.Drug Action / Absorption 7.Site of Drug Partitioning Considering pH Effects Alone

39 General Paritioning Concepts  The partition law : a solute will distribute itself between two immiscible solvents so that the ratio of its conc. in each solvent is equal to the ratio of its solubility in each one C o = molar conc. in organic layer C w = molar conc. in aqueous layer K d = partition coefficient or distribution constant

40 For Strong / Nonelectrolytes as Solutes Strong Electrolyte  Strong electrolytes are completely dissociated in aqueous solution → cations & anions in aqueous layer → water soluble  Without ion pairing, do not partition into the organic layer Nonelectrolyte

41 For Weak Electrolytes as Solutes  The partition law : depends on pH  pH different from pK a (pH pK a for weak base)  For a weak organic acid,  For a weak organic base,

42 Application of Distribution Concepts  Preservation of Emulsions The total preservative added = C, where C = C 0 + C w

43 Drug Action / Absorption  Drug Action ; by passive diffusion ; due only to a concentration gradient across the barrier  Drug Absorption ; water solubility of the drug, the lipid/water partition coefficient of the drug molecule, MW, chemical structure ; drugs must be in solution in aqueous intestinal fluids

44 Site of Drug Partitioning Considering pH Effects Alone  Absorption from the stomach (pH 1-3)  Absorption from the intestines (pH 4-6)  Urinary Excretion (pH 5-7)  Excretion of drugs in sweat (pH 5-7)  Excretion of drugs in human milk (pH 6.6)  Rectal administration (pH 7.8)


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