PHT 224 Pharmaceutics I Dr. Saleh Al-Suwayeh Phone: Office hours: Every day 12:30-1:00 pm

Text Books: Remington, 21st edition and Physical Pharmacy By Alfred Martin

Pharmaceutics I Learning Objectives: -To define scientifically Solubility and understand the physicochemical aspects of solution formation process; -To describe different solubility expressions; -To identify different solvents, additives and techniques used to enhance solubility; -To understand colligative properties of solution and isotonic solutions; -To understand solution stability and reaction rates and reaction orders; -To understand effect of storage on stability of solutions.

Materials (solutes&solvents) may be mixed to form True solution Homogenous mixture e.g. NaCl-water solution Colloidal solution Homogenous mixture Heterogeneous mixture Coarse dispersion Heterogeneous mixture According to particle size, liquid dosage forms are classified into

Solubility Definitions Solute: is a substance to be dissolved in a solvent to give a solution e.g., NaCl Solvent: refers to a substance that dissolves a solute to give a solution e.g., Water. Dissolution: The process of dissolving a solute in a solvent to form a homogeneous solution Heterogeneous systems : These are systems also encountered in pharmacy and called course dispersions e.g., emulsions and suspensions. Solubility: Quantitative: The maximum concentration to which a solution can be prepared at a given temperature.

Qualitative: the sponteneous interaction between two or more components to form a homogeneous solution. Solution: is a mixture of two or more substances that form a homogenous molecular dispersion system (one phase). Binary solution: refers to a solution composed of two substances. The component present in the greater amount in a binary system is designated as the solvent and the component in the lesser amount as the solute. When water is one of the constituents of a liquid mixture, it is usually considered the solvent. It is less meaningful to classify the components as solute and solvent when dealing with mixture of liquid that are miscible in all proportions, such as alcohol and water. States of matter: There are three states of the matter: Solid, liquid and gas and all these can act as either solute or solvent in a solution

Solute Examples of solutions SolidLiquidGas Air freshners eg p=dichlorobenzene in air Water vapor in air (Respirator) Oxygen and other gases in nitrogen (air), Aneasthetic gas (N2O) Gas Solvent Sucrose (table sugar) in water; sodium chloride (table salt) in water; Ethanol (common alcohol) in water Carbon dioxide in water (carbonated water) Liquid Thymol (50 0 C) and salol (40 0 C)mixture used as mild antiseptic Liquid paraffin in paraffin wax used as ointment base. Hydrogen dissolves rather well in metals eg., palladium and platinum. Solid

States of matter and intermolecular forces: Gas: Molecules in a gas attract each other, but the attractive forces are weak compared with the thermal motion of the molecules so the molecules spread out evenly to fill the container enclosing them, however if a gas is cooled, the thermal motion will decrease and the gas will first liquify and then it will solidify. Liquids: Liquids have sufficient attractive forces to stay in an open container but they can still flow. Properties such as viscosity and its inverse fluidity are measures of the attractive forces in liquids. E.g., glycols are very viscous, while hexane flows very easily. Solids: Solids have enough attractive forces called crystal lattice energy that they do not even flow, e.g., magnesium stearate is a lubricant needed to ease movement of drug powder in tableting machine.

Types of solutions based on concentration Saturated solution: is a solution in which the dissolved solute and the solid phase (un- dissolved solute) is in equilibrium. Super-saturated solution: is a solution contains more of the dissolved solute than it would normally contain at a definite temperature, were the un-dissolved solute present. e.g. salts such as sodium thiosulfate and sodium acetate can be dissolved in large amounts at an elevated temperature and upon cooling, fail to crystallise from the solution. Un-saturated (sub-saturated) solution: is a solution in which the dissolved solute in a concentration below that necessary for complete saturation at a definite temperature. Concentrated solution: is a solution that contains a large amount of solute relative to the amount that could dissolve. Diluted solution: is a solution that contains a relatively low concentration of solute. Stock solution In chemistry, a stock solution is a large volume of a common reagent, such as hydrochloric acid or sodium hydroxide, at a standardized concentration.