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PHYSICAL PHARMACY Lab Notes PHASE DIAGRAM FOR SYSTEMS CONTAINING LIQUID PHASES EXERCISE # 1 PHASE DIAGRAM Used to formulate systems containing more than one component where it may be advantageous to achieve a single liquid-phase product. PHASE DIAGRAM Phase diagr...

PHYSICAL PHARMACY Lab Notes PHASE DIAGRAM FOR SYSTEMS CONTAINING LIQUID PHASES EXERCISE # 1 PHASE DIAGRAM Used to formulate systems containing more than one component where it may be advantageous to achieve a single liquid-phase product. PHASE DIAGRAM Phase diagrams have several important applications in pharmacy, particularly in the formulation and development of pharmaceutical products. Applications of Phase Diagram Formulation Development  Solubility Optimization: Phase diagrams help in identifying the solubility of drugs in various solvents and excipients. This information is crucial for developing formulations, such as solutions, suspensions, and emulsions, where solubility plays a key role in the drug's effectiveness.  Choice of Solvent Systems: In liquid formulations, phase diagrams guide the selection of solvent systems that ensure the drug remains in solution under various storage conditions. Applications of Phase Diagram Polymorphism and Crystallization  Polymorph Identification: Many drugs can exist in different crystalline forms (polymorphs), which may have different solubilities and stabilities. Phase diagrams help in understanding the conditions under which different polymorphs form, enabling the selection of the most stable and therapeutically effective form.  Control of Crystallization: Phase diagrams are used to control crystallization processes during the manufacturing of drugs, ensuring consistent particle size and morphology, which are important for drug bioavailability. Applications of Phase Diagram Stability Studies  Predicting Phase Transitions: Phase diagrams help predict phase transitions, such as solid- liquid or liquid-liquid transitions, that may affect drug stability. Understanding these transitions helps in designing stable dosage forms.  Prevention of Incompatibilities: By studying phase diagrams, pharmacists can predict and prevent potential incompatibilities between drug components, which could lead to degradation or reduced efficacy. Applications of Phase Diagram Solid Dispersions and Amorphous Systems  Improvement of Dissolution Rates: Phase diagrams are used in the development of solid dispersions, where a drug is dispersed in a carrier matrix to improve its dissolution rate. Understanding the phase behavior helps in selecting the right carrier and processing conditions.  Amorphous Drug Formulations: Phase diagrams help in stabilizing amorphous forms of drugs, which can have higher solubility than their crystalline counterparts. They guide the selection of excipients and processing methods to maintain the drug in its amorphous state. Applications of Phase Diagram Emulsion and Suspension Stability  Optimizing Emulsion Stability: Phase diagrams are used to identify the right proportions of oil, water, and emulsifier to create stable emulsions, which are common in topical and oral drug formulations.  Suspension Formulation: For suspensions, phase diagrams help in understanding the conditions under which the suspended particles remain uniformly distributed and do not settle out or agglomerate. Applications of Phase Diagram Controlled Release Systems  Design of Controlled Release Formulations: Phase diagrams assist in designing controlled release formulations by helping to understand the interaction between the drug and polymer matrices. This information is used to control the release rate of the drug from the formulation. Temperature-composition diagram for system consisting of water and phenol Curve gbhci – limits of temperature and concentration within which two liquids exists in equilibrium Region outside the curve contains systems having one liquid phase Temperature-composition diagram for system consisting of water and phenol At point a, adding increments of phenol to a fixed weight of water will result in the formation of a single liquid phase until point be is reached. Once the total concentration of phenol exceeds 63% at 50oC, a single phenol-rich liquid phase is formed. CRITICAL SOLUTION TEMPERATURE Upper consolute Temperature The maximum temperature at which the two- phase region exists. In the case of phenol-water system, all combinations of phenol and water above 66.8oC are completely miscible and yield one-phase liquid systems. CRITICAL SOLUTION TEMPERATURE The Critical Solution Temperature (CST), also known as the consolute temperature, is the temperature above or below which the components of a mixture become completely miscible in all proportions. This concept is often used in the context of partially miscible liquid-liquid systems. There are two types of CST:  Upper Critical Solution Temperature (UCST): This is the highest temperature at which phase separation occurs. Above the UCST, the components of the mixture are completely miscible in all proportions.  Lower Critical Solution Temperature (LCST): This is the lowest temperature at which phase separation occurs. Below the LCST, the components of the mixture are completely miscible. Temperature-composition diagram for system consisting of water and phenol The tie line is always parallel to the base line in two-component system. All systems prepared on a tie line at equilibrium, will separate into phases of constant composition (conjugate phases). Temperature-composition diagram for system consisting of water and phenol Any system represented by a point on the line at 50oC separates to give a pair of conjugate phases. PHASE DIAGRAM In a ternary phase diagram, the three components (water, butanol, and acetone) are represented as the three corners of an equilateral triangle. The composition of the mixture is shown as a point within this triangle.  PHASE EQUILIBRIA IN THREE B COMPONENT SYSTEMS Each of the three corners or apexes of the triangle represents 100% by weight of one component (A,B, or C). As a result, the same apex will represent 0% of A C the other two components.  PHASE EQUILIBRIA IN THREE B COMPONENT SYSTEMS The three lines joining the corner points represent two component mixtures of the three possible combinations of A, B, and C. Thus the lines AB, BC, and CA are used for two component mixtures of A and B, B and C, and C and A, respectively. A C  PHASE EQUILIBRIA IN THREE B COMPONENT SYSTEMS The area within the traingle represents all the possible combinations of A, B, and C to give three component systems. A C  PHASE EQUILIBRIA IN THREE B COMPONENT SYSTEMS If a line is drawn through any apex to a point on the opposite side, then all systems represented by points on such a line have a constant ratio of two components. A C  PHASE EQUILIBRIA IN THREE B COMPONENT SYSTEMS Any line drawn parallel to one side of the triangle represents ternary system in which the proportion of one component is constant. A C  TERNARY SYSTEMS WITH ONE PAIR OF PARTIALLY MISCIBLE LIQUIDS Water and acetone are miscible only to a slight extent, and so a mixture of the two usually produces a two-phase system. The heavier of the two phases consists of water saturated with benzene, while the lighter phase is benzene saturated with water.  TERNARY SYSTEMS WITH ONE PAIR OF PARTIALLY MISCIBLE LIQUIDS Alcohol is completely miscible with both acetone and water. Therefore, the addition of sufficient alcohol to a two-phase system of benzene and water would produce a single liquid phase in which all three components are miscible.  TERNARY SYSTEMS WITH ONE PAIR OF PARTIALLY MISCIBLE LIQUIDS alcohol Binary mixtures of water and acetone Limits of solubility of water and acetone acetone water Miscibility Zones  Water-Butanol-Acetone Mixtures: The phase diagram will typically display regions where different phases (liquid-liquid, single phase) are present. For this specific system:  a. Single Liquid Phase Regions:  Water and Acetone: In the presence of butanol, you can often achieve a single liquid phase. Acetone and butanol are both fully miscible, and butanol and water are partially miscible. The interaction between these components can lead to regions in the phase diagram where a single liquid phase exists.  b. Two-Phase Regions:  Water and Butanol: When the butanol content is high relative to water, especially if acetone is also present, you might encounter a two-phase system where water and butanol separate into distinct phases.  Water and Acetone: When acetone is in excess compared to water, and butanol is also present, two liquid phases can form, one rich in water and butanol, and the other rich in acetone.  TERNARY SYSTEMS WITH ONE PAIR OF PARTIALLY MISCIBLE LIQUIDS alcohol BINODAL CURVE – marks the extent of the two phase region. The remainder of the triangle acetone contains one liquid phase water Boundaries and Curves  Binodal Curves: The boundaries of the single-phase and two-phase regions are represented by curves within the ternary diagram. These curves indicate the compositions at which phase separation occurs.  a. The binodal curve for water-butanol-acetone will generally show a region where you have complete miscibility and a region where phase separation occurs.  Tie Lines: In the two-phase regions, tie lines connect points on the binodal curve that are in equilibrium with each other. These lines represent the compositions of the coexisting phases.  TERNARY SYSTEMS WITH ONE PAIR OF PARTIALLY MISCIBLE LIQUIDS alcohol The system will separate into two phases after reaching equilibrium. acetone water  TERNARY SYSTEMS WITH ONE PAIR OF PARTIALLY MISCIBLE LIQUIDS alcohol The addition of alcohol into the mixture will produce a phase change from a two-liquid system acetone to a one-liquid system. water  TERNARY SYSTEMS WITH ONE PAIR OF PARTIALLY MISCIBLE LIQUIDS alcohol With a 25:75 mixture of water and acetone, the addition of alcohol leads to a change. acetone water  TERNARY SYSTEMS WITH ONE PAIR OF PARTIALLY MISCIBLE LIQUIDS alcohol All mixtures will be one-phase systems. acetone water Critical Points Critical Points: In some ternary phase diagrams, you might observe a critical point where the transition from one phase to two phases happens under specific conditions of temperature and pressure. TERNARY SYSTEMS WITH TWO OR THREE PAIRS OF PARTIALLY MISCIBLE LIQUIDS Phase Behavior Understanding the phase behavior of the water-butanol- acetone system is useful in applications like solvent extraction, formulation of pharmaceuticals, and industrial processes where the separation or mixing of these solvents is important. Summary The phase diagram of the water-butanol-acetone system will typically show:  Regions of complete miscibility (single liquid phase) where all three components mix thoroughly.  Regions of partial miscibility or phase separation (two-liquid phases) where water, butanol, and acetone separate into distinct phases depending on their proportions and interactions.  Binodal curves and tie lines that define the phase boundaries and the compositions of coexisting phases. This ternary phase diagram provides a visual representation of how different compositions of water, butanol, and acetone interact and behave under various conditions. ANSWERS to QUESTIONS 1. What is critical solution temperature (CST)? The Critical Solution Temperature (CST), also known as the consolute temperature, is the temperature above or below which the components of a mixture become completely miscible in all proportions. This concept is often used in the context of partially miscible liquid- liquid systems. ANSWERS to QUESTIONS 2. At what temperature and concentration does phenol-water system exist as one liquid pair? At 66.8°C and a phenol concentration of around 33.3% by weight, the phenol-water system will exist as one liquid phase, meaning the mixture is homogenous and does not separate into two phases. ANSWERS to QUESTIONS 3. What is the effect of (a) n-butanol in water-acetone liquid pair? n-butanol acts as a cosolvent that increases the compatibility of water and acetone, potentially leading to a more uniform and stable mixture. The addition of n-butanol to a water-acetone liquid pair has a significant effect on the solubility and miscibility of the two components:  Increase in Mutual Solubility: n-Butanol is a medium-chain alcohol that is miscible with both water and acetone. When n-butanol is added to a water-acetone mixture, it acts as a cosolvent, increasing the mutual solubility of water and acetone. This is because n-butanol has both hydrophilic (water-attracting) and hydrophobic (water- repelling) properties, allowing it to interact with both polar water molecules and less polar acetone molecules.  Decrease in Phase Separation: Due to the enhanced mutual solubility, the addition of n-butanol can reduce or even eliminate the tendency of water and acetone to separate into two distinct phases, particularly at certain concentrations. This makes the mixture more homogeneous.  Potential Formation of a Single Phase: With an appropriate amount of n-butanol, the water-acetone-n-butanol mixture may exist as a single liquid phase across a wider range of concentrations and temperatures, compared to the water-acetone pair alone. ANSWERS to QUESTIONS 3. What is the effect of (b) water in n-butanol-acetone liquid pair? The addition of water to an n-butanol-acetone liquid pair generally leads to a decrease in miscibility and may induce phase separation, depending on the amount of water added and the specific concentrations of n-butanol and acetone in the mixture. The effect of adding water to an n-butanol-acetone liquid pair can be understood in terms of the changes it induces in the miscibility and phase behavior of the mixture:  Decreased Miscibility: Water is polar, and its miscibility with acetone (a moderately polar solvent) and n-butanol (which has both polar and nonpolar characteristics) depends on the balance of interactions. Adding water to the n-butanol-acetone system typically decreases the miscibility of the components because water tends to preferentially interact with itself due to strong hydrogen bonding. This can lead to phase separation, particularly if the amount of water is significant.  Potential for Phase Separation: At certain concentrations, water can cause the n-butanol- acetone system to separate into two phases. This happens because water and acetone are only partially miscible, and the presence of n-butanol, which can mix with both to some extent, may not be sufficient to maintain a single-phase system as more water is added.  Influence on Solubility Parameters: Water can alter the solubility parameters of the n-butanol- acetone mixture. Since water has a high dielectric constant, its addition can shift the balance of solubility, making the system more likely to exhibit immiscibility or decreased solubility of certain components. ANSWERS to QUESTIONS 4. What is the application of phase diagram in pharmacy? Phase diagrams are essential tools in pharmacy for optimizing drug formulations, ensuring stability, and designing effective and safe pharmaceutical products. SPECIFIC GRAVITY DETERMINATION EXERCISE # 2 SPECIFIC GRAVITY Specific gravity is the ratio of the density of a substance to the density of water. The density of both the substances should be recorded at the same temperature unless specified. It is also called relative density.  HYDROMETER  WESTPHAL BALANCE Specific gravity determination using Hydrometers Be sure the Hydrometer is clean and dry. Place enough sample liquid in a 100mL graduated cylinder. Immerse the Hydrometer slowly in liquid to a point below which it naturally sinks. Do not make reading until the hydrometer and liquid are at rest and free from air bubbles. Read the specific gravity of the sample liquid directly from the calibration of the instrument. ANSWERS to QUESTIONS 1. Liquids are easier to measure than weighing. The specific gravity figure can be utilized to calculate the density (or weight per ml) of liquid substance. The weight can be converted to volume and volume equivalent to weight can be easily measured. ANSWERS to QUESTIONS  2. According to this principle the buoyant force on an object equals the weight of the fluid it displaces. When a body is immersed partially or completely in a liquid, the apparent loss of weight of the body is equal to the weight of the liquid displaced. In other words, any object, wholly or partly immersed in a liquid, is buoyed up by a force equal to the weight of the liquid displaced by the object. This principle can be used to find out the density (or the specific gravity) of a body made of a particular material.  3. At higher temperatures the kinetic energies of the molecules making up a substance will be higher, and thus the molecules will occupy a larger volume SOLUBILITY OF DRUGS EXERCISE # 3 SOLUBILITY OF DRUGS SOLUBILITY - is defined in quantitative terms as the concentration of solute in a saturated solution at a certain temperature - qualitative way, it can be defined as the spontaneous interaction of two or more substances to form a homogeneous molecular dispersion. SOLUBILITY OF DRUGS SOLUBILITY - is an intrinsic material property that can be altered only by chemical modification of the molecule. - dissolution is an extrinsic material property that can be influenced by various chemical, physical, or crystallographic means such as complexation, particle size, surface properties, solid-state modification, or solubilization enhancing formulation strategies. Importance of Solubility to Pharmacy a. Permits the pharmacist to choose the best solvent medium for a drug or combination of drugs. b. Helps in overcoming difficulties which arises in the preparation of pharmaceutical solution c. Serves as standard or test of purity A. Solubility of Solids in Liquids A. Solubility of Solids in Liquids A. Solubility of Solids in Liquids  “Like dissolves Like” Polar solvents dissolve ionic solutes and other polar substances. Non polar compounds can dissolve non polar solutes like oils and fats, carbon tetrachloride, benzene, mineral oil, alkaloidal bases and fatty acids. A. Solubility of Solids in Liquids The boiling point of liquids and the melting point of solids both reflect the strengths of interactions between the molecules in the pure liquid or the solid state. In general, aqueous solubility decreases with increasing boiling point and melting point. A. Solubility of Solids in Liquids The influence of substituents on the solubility of molecules in water can be due to their effect on the properties of the solid or liquid or to the effect of the substituent on its interaction with water molecules. Polar groups such as –OH capable of hydrogen bonding with water molecules impart high solubility. Non-polar groups such as –CH3 and –Cl are hydrophobic and impart low solubility. B. Solubility of Liquids in Water B. Solubility of Liquids in Water Frequently two or more liquids are mixed together in the preparation of pharmaceutical solutions. Examples: Alcohol is added to water to form hydroalcoholic solutions of various concentrations. Volatile oils are mixed with water to form dilute solutions known as aromatic waters, Volatile oils are added to alcohol to yield spirits and elixirs. Ether and alcohol are combined in collodions. MISCIBILITY  It refers to the mutual solubilities of the component in liquid-liquid systems. a. COMPLETE MISCIBILITY – mix in all proportions (ex. Water/Alcohol, Water/Acetone, Benzene/CCl4) b. PARTIAL MISCIBILITY – certain proportions are mixed (ex. Phenol/Water, Diethyl ether/Water, Mineral oil/Water) c. IMMISCIBLE – water and liquid petrolatum B. Solubility of Liquids in Water Water + Phenol = PARTIALLY MISCIBLE  The upper critical solution temperature (UCST) or upper consolute temperature is the critical temperature above which the components of a mixture are miscible in all proportions.  All combinations of phenol and water are completely miscible at 66.8°C C. EFFECT OF TEMPERATURE C. EFFECT OF TEMPERATURE C. EFFECT OF TEMPERATURE C. EFFECT OF TEMPERATURE  POSITIVE HEAT – solubility increases with increasing temperature. For substances that exhibit endothermic reaction. Most of the salts show positive heat.  NEGATIVE HEAT – solubility increases with decreasing temperature. For substance that exhibit exothermic reaction. Salts like calcium sulfate and calcium hydroxide show negative heat.  When heat is neither absorbed nor given off, the solubility is not affected by variation of temperature as is nearly the case with sodium chloride. Exothermic and Endothermic D. EFFECT OF OTHER SUBSTANCE D. EFFECT OF OTHER SUBSTANCE  Hydroxy acids, such as tartaric and citric acids, are quite soluble in water because they are solvated through their hydroxyl groups.  Sodium citrate is used to dissolve water-insoluble acetylsalicylic acid because the soluble acetylsalicylate ion is formed in the reaction.  Acetylsalicylic acid (ASA) + Water --> Insoluble  ASA + Water + Na citrate --> Soluble (acetylsalicylate) D. EFFECT OF OTHER SUBSTANCE Salting Out  It is a phenomenon by which gases are often liberated from solutions in which they are dissolved by the introduction of an electrolyte such as sodium chloride and sometimes by a non-electrolyte such as sucrose.  The resultant escape of gas is due to the attraction of the salt ions or the highly polar non-electrolyte for the water molecules, which reduces the density of the aqueous environment adjacent to the gas molecules. Influence of Foreign Substances The addition of a substance to a binary liquid system produces a ternary system, i.e., one having three components.  1- If the added material is soluble in only one of the two components, the mutual solubility of the liquid pair is decreased.  2- If the original binary mixture has an upper critical solution temp., the temperature is raised by addition of of the third component  3- if it has a lower consolute temp., it is lowered by the addition of the third component. For example, if naphthalene is added to a mixture of phenol and water, it dissolves only in the phenol and raises the consolute temp. If potassium chloride is added to a phenol-water mixture, it dissolves only in water and raises the consolute temp. When the third substance is soluble in both of the liquids to roughly the same extent, the mutual solubility of the liquid pair is increased, an upper critical solution temp. is lowered and a lower critical solution temp. is raised. Ex. The addition of succinic acid or sodium oleate to a phenol-water system. COMMON-ION EFFECT This refers to the effect of adding an ion common to one already in equilibrium in a solubility reaction is to lower the solubility of the salt. It is responsible for the reduction in the solubililty of an ionic precipitate when a soluble compound combining one of the ions of the precipitate is added to the solution in equilibrium with the precipitate.  E. EFFECT OF pH  At low pH, protonation of the anion can dramatically increase the solubility of the salt. E. EFFECT OF pH E. EFFECT OF pH E. EFFECT OF pH  Most important drugs are weak acids or bases. pH is one of the primary influences on the solubility of most drugs that contain ionizable groups.  Acidic drugs, such as the penicillin and NSAIDs are less soluble in acidic solutions than in alkaline solutions because the predominant undissociated (unionized) species cannot interact with water molecules to the same extent as the ionized form which is readily hydrated.  Acidic Drugs + Acid (low pH) --> Precipitates (decreased solubility)  Basic drugs such as diphenhydramine, ranitidine and antacids are more soluble in acidic solutions where the ionized form of the drug is predominant.  Basic Drugs + Acid (low pH) --> Dissolves (increased solubility) E. EFFECT OF pH  Acid + Acid --> Unionized (lipophilic/ water-insoluble)  Acid + Base --> Ionized (hydrophilic/ water-soluble)  Factors Affecting Solubility of Drugs a. Physicochemical properties of the solute and the solvent b. Temperature c. Pressure d. pH of the solution e. Presence of other substance to aid solubility a) Physicochemical properties of the drug  Ionized vs. Unionized forms - lower ionic strengths favors solubility; solubility occurs faster with salts  Particle size - smaller particles increase surface area in contact resulting to solubility  Crystalline state - amorphous form favors solubility  Drug complexes - complexes like cyclodextrins enhance absorption c) Effect of Pressure:  The effect of the pressure on the solubility of a gas is expressed by Henry's Law, which states that at constant temp, the concentration of dissolved gas is proportional to the partial pressure of the gas above the solution at equilibrium.  Importance of Henry's law in pharmacy: Solubility of a gas increases directly as the pressure of the gas in the solution is increased and conversely, that the solubility of the gas decreases so that sometimes the gas escapes with violence when the pressure above the solution is released.  This phenomenon is commonly recognized in effervescent solutions when the stopper of the container is removed. d) pH  Weakly basic drugs dissolve rapidly in a low pH environment. For weak bases: Solubility decreases with increasing pH  Weakly acidic drugs dissolve well in a high pH environment. For weak acids: Solubility increases with increasing pH e) Presence of other substance to aid solubility Frequently a solute is more soluble in a mixture of solvents than in one solvent alone. This phenomenon is known as cosolvency, and the solvents that, in combination, increase the solubility of the solute are called cosolvents. ANSWERS to QUESTIONS 1. Importance of Solubility to Pharmacy a. Permits the pharmacist to choose the best solvent medium for a drug or combination of drugs. b. Helps in overcoming difficulties which arises in the preparation of pharmaceutical solution c. Serves as standard or test of purity ANSWERS to QUESTIONS 2. “Like dissolves Like” Polar solvents dissolve ionic solutes and other polar substances. Non polar compounds can dissolve non polar solutes like oils and fats, carbon tetrachloride, benzene, mineral oil, alkaloidal bases and fatty acids. ANSWERS to QUESTIONS 3. Factors Affecting Solubility of Drugs a. Physicochemical properties of the solute and the solvent b. Temperature c. Pressure d. pH of the solution e. Presence of other substance to aid solubility a) Physicochemical properties of the drug  Ionized vs. Unionized forms - lower ionic strengths favors solubility; solubility occurs faster with salts  Particle size - smaller particles increase surface area in contact resulting to solubility  Crystalline state - amorphous form favors solubility  Drug complexes - complexes like cyclodextrins enhance absorption c) Effect of Pressure  The effect of the pressure on the solubility of a gas is expressed by Henry's Law, which states that at constant temp, the concentration of dissolved gas is proportional to the partial pressure of the gas above the solution at equilibrium.  Importance of Henry's law in pharmacy: Solubility of a gas increases directly as the pressure of the gas in the solution is increased and conversely, that the solubility of the gas decreases so that sometimes the gas escapes with violence when the pressure above the solution is released.  This phenomenon is commonly recognized in effervescent solutions when the stopper of the container is removed. pH  Weakly basic drugs dissolve rapidly in a low pH environment. For weak bases: Solubility decreases with increasing pH  Weakly acidic drugs dissolve well in a high pH environment. For weak acids: Solubility increases with increasing pH Presence of other substance to aid solubility Frequently a solute is more soluble in a mixture of solvents than in one solvent alone. This phenomenon is known as cosolvency, and the solvents that, in combination, increase the solubility of the solute are called cosolvents. 4. Exothermic and Endothermic 5. Ideal and Non-Ideal Solution  IDEAL SOLUTION Obey Raoult's law at every range of concentration; neither heat is evolved nor absorbed during dissolution total volume of solution is equal to sum of volumes of the components Examples: Dilute solutions; benzene + toluene; n-hexane + n-heptane; chlorobenzene + bromobenzene; ethyl bromide + ethyl iodide; n-butyl chloride + n-butyl bromide  NON-IDEAL SOLUTION Do not obey Raoult's law at every range of concentration; Either heat is evolved or absorbed during dissolution Either volume of solution is increased after dissolution or decreased during dissolution Examples: Acetone +ethanol; water + methanol; water + ethanol; acetone + benzene; cyclohexane + ethanol Examples: Acetone + aniline; acetone + chloroform; chloroform + diethyl ether; water + HCl; acetic acid + pyridine; chloroform + benzene 6. COMMON-ION EFFECT The solubility of a sparingly soluble salt is reduced in a solution that contains an ion in common with that salt AgCl + H2O = soluble AgCl + H2O + NaCl → AgCl (ppt) + NaCl (aq. Sol’n) Except: CuCl + H2O → CuCl (ppt) + H2O CuCl + H2O + 2HCl → CuCl2 + H2O