Physical Pharmacy Solutions Khalid T Maaroof MSc. Pharmaceutical sciences School of pharmacy Pharmaceutics department 10/31/2015 Online access: bit.ly/physicalpharmacy 1
Mixtures a combination of two or more substances that do not combine chemically, and can be separated by physical means Two types: 2 Heterogeneous Homogeneous
Heterogeneous Mixture Hetero means different consists of visibly different substances or phases (solid, liquid, gas) a suspension is a special type of heterogeneous mixture of larger particles that eventually settle Example: 3
Homogeneous Mixture Homo means the same has the same uniform appearance and composition throughout; maintain one phase (solid, liquid, gas) Commonly referred to as solutions Example: Salt Water 4 Notice the uniform appearance
Solution a mixture of two or more substances that is identical throughout Salt water is can be physically separated considered a solution. How composed of solutes and solvents can it be physically separated? the substance in the smallest amount and the one that dissolves in the solvent Iced Tea Mix (solute) the substance in the larger amount that dissolves the solute Iced Tea (solution) Water (solvent )
Solutions 6
Types of solutes Electrolytes (Conductive): Dissociation in to ions in solution Eg: NaCl Nonelectrolytes (no conductivity): no dissociation Eg: suger Na + Cl -
Concentration the amount of solute dissolved in a solvent at a given temperature described as dilute if it has a low concentration of solute described as saturated if it has a high concentration of solute described as supersaturated if contains more dissolved solute than normally possible
Concentration expressions for solutions Molarity? Normality? Molality? Mole fraction? Mole percent? Percent 9 Percent by weight % w/w Percent by volume %v/v Percent weight in volume % w/v
Concentration expressed as percentage Percent weight-in-weight (w/w) is the grams of solute in 100 grams of the solution. Percent weight-in-volume (w/v) is the grams of solute in 100ml of the solution. Percent volume-in-volume (v/v) is the milliliters of solute in 100ml of the solution. A 20 % w/w solution contains 20g solute how many grams the solvent is? 10
Molarity, Normality, and Molality Molarity and normality both depend on the volume of the solvent, so their values are affected by change of volume caused by factors such as change in temperature. Molality doesn t has this disadvantage. 11
Mole fraction In a solution containing 0.01 mole of solute and 0.04 mole of solvent, the mole fraction of the solute is 0.2 and for solvent it is 0.8 Mole percent = mole fraction X 100 12
An aqueous solution of ferrous sulfate was prepared by adding 41.50 g of FeSO4 to enough water to make 1000 ml of solution. The density of the solution is 1.0375 and the molecular weight of FeSO4 is 151.9. Calculate (a) molarity (b) molality (c) mole fraction of FeSO4, mole fraction of water, and the mole percent of the two constituents (d) % w/w of FeSO4. 13
Solutes Change Solvents The amount of solute in a solution determines how much the physical properties of the solvent are changed Examples: Lowering the Freezing Point The freezing point of a liquid solvent decreases when a solute is dissolved in it. Ex. Pure water freezes at (0 0C), but when salt is dissolved in it, the freezing point is lowered. This is why people use salt to melt ice. Raising the Boiling Point The boiling point of a solution is higher than the boiling point of the solvent. Therefore, a solution can remain a liquid at a higher temperature than its pure solvent. Ex. The boiling point of pure water is (100 0 C), but when salt is dissolved in it, the boiling point is higher. This is why it takes salt water longer to boil than fresh water. Those physical properties of solution that are changed by the amount of solute are called colligative properties
15 Colligative properties
Colligative properties Colligative properties of solutions are those that affected (changed) by the presence of solute and depend solely on the number (amount of solute in the solutions) rather than nature of constituents. Examples of colligative properties are: Vapor pressure Boiling point Freezing point Osmotic pressure 16
Colligative vs Non-colligative Compare 1.0 M aqueous sugar solution to a 0.5 M solution of salt (NaCl) in water. both solutions have the same number of dissolved particles any difference in the properties of those two solutions is due to a non-colligative property. Both have the same freezing point, boiling point, vapor pressure, and osmotic pressure 17
Non-Colligative Properties Sugar solution is sweet and salt solution is salty. Therefore, the taste of the solution is not a colligative property. Another non-colligative property is the color of a solution. Other non-colligative properties include viscosity, surface tension, and solubility. 18
vapor pressure Vapor pressure: Pure solvent > solutions
Vapor pressure of solvent in solution containing non-volatile solute is always lower than vapor pressure of pure solvent at same T At equilibrium rate of vaporization = rate of condensation Solute particles occupy volume reducing rate of evaporation. (They limit the number of solvent molecules at the surface) The rate of evaporation decreases and so the vapor pressure above the solution must decrease to recover the equilibrium
Boiling point Boiling point elevation is a colligative property related to vapor pressure lowering. The boiling point is defined as the temperature at which the vapor pressure of a liquid equals the atmospheric pressure. Due to vapor pressure lowering, a solution will require a higher temperature to reach its boiling point than the pure solvent. 21
Freezing Point Every liquid has a freezing point - the temperature at which a liquid undergoes a phase change from liquid to solid. When solutes are added to a liquid, forming a solution, the solute molecules disrupt the formation of crystals of the solvent. That disruption in the freezing process results in a depression of the freezing point for the solution relative to the pure solvent. 22
H ow this is d one?
1. salting roads in winter water water + a little salt water + more salt FP 0 o C (NFP) BP 100 o C (NBP) 11 o C 103 o C 18 o C 105 o C 2. antifreeze (AF) / coolant water FP 0 o C (NFP) BP 100 o C (NBP) water + a little AF 10 o C 110 o C 50% water + 50% AF 35 o C 130 o C
What happens to the triple point? 25
Which is more effective for lowering the freezing point of water? NaCl or CaCl 2 or Glucose Ionic solutes produce two or more ion particles in solution. They affect the colligative properties proportionately more than molecular solutes (that do not ionize). The effect is proportional to the number of particles of the solute in the solution. 26
Osmotic Pressure When a solution is separated from a volume of pure solvent by a semi-permeable membrane that allows only the passage of solvent molecules, the height of the solution begins to rise. The value of the height difference between the two compartments reflects a property called the osmotic pressure of a solution. 27
Osmotic Pressure and Cells In the figure, red blood cells are placed into saline solutions. 1. In which case (hypertonic, isotonic, or hypotonic) does the concentration of the saline solution match that of the blood cells? 2. In which case is the saline solution more concentrated than the blood cells? Crenation Hemolysis
Questions! 29 10/31/2015