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Physical Pharmacy Solutions Khalid T Maaroof

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1 Physical Pharmacy Solutions Khalid T Maaroof
MSc. Pharmaceutical sciences School of pharmacy – Pharmaceutics department Online access: bit.ly/physicalpharmacy 10/31/2015

2 Two types: Heterogeneous Homogeneous Mixtures
a combination of two or more substances that do not combine chemically, and can be separated by physical means Two types: Heterogeneous Homogeneous

3 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:

4 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: Notice the uniform appearance Salt Water

5 Solution a mixture of two or more substances that is identical throughout can be physically separated composed of solutes and solvents Salt water is considered a solution. How can it be physically separated? the substance in the smallest amount and the one that dissolves in the solvent the substance in the larger amount that dissolves the solute Iced Tea Mix (solute) Water (solvent) Iced Tea (solution)

6 Solutions

7 Types of solutes Dissociation in to ions in solution Eg: NaCl
Electrolytes (Conductive): Dissociation in to ions in solution Eg: NaCl Nonelectrolytes (no conductivity): no dissociation Eg: suger Na+ Cl-

8 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 described as supersaturated if contains more dissolved solute than normally possible

9 Concentration expressions for solutions
Molarity? Normality? Molality? Mole fraction? Mole percent? Percent Percent by weight % w/w Percent by volume %v/v Percent weight in volume % w/v

10 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?

11 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.

12 Mole fraction In a solution containing 0.01 mole of solute and 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

13 An aqueous solution of ferrous sulfate was prepared by adding 41
An aqueous solution of ferrous sulfate was prepared by adding g of FeSO4 to enough water to make mL of solution. The density of the solution is and the molecular weight of FeSO4 is 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.

14 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 Raising the Boiling Point The freezing point of a liquid solvent decreases when a solute is dissolved in it. Ex. Pure water freezes at (00C), but when salt is dissolved in it, the freezing point is lowered. This is why people use salt to melt ice. 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 (1000C), 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

16 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

17 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 Compare 1.0 M aqueous sugar solution to a 0.5 M solution of table salt (NaCl) in water. Despite the concentrations, both solutions have precisely the same number of dissolved particles because each sodium chloride unit creates two particles upon dissolution - a sodium ion, Na+, and a chloride ion, Cl-. Therefore, any difference in the properties of those two solutions is due to a non-colligative property. Both solutions have the same freezing point, boiling point, vapor pressure, and osmotic pressure because those colligative properties of a solution only depend on the number of dissolved particles.

18 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.

19 Pure solvent > solutions
vapor pressure Vapor pressure: Pure solvent > solutions

20 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

21 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.

22 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.

23 How this is done?

24 1. salting roads in winter FP BP water 0oC (NFP) 100oC (NBP)
water + a little salt –11oC 103oC water + more salt –18oC 105oC 2. antifreeze (AF) /coolant FP BP water 0oC (NFP) 100oC (NBP) water + a little AF –10oC 110oC 50% water + 50% AF –35oC 130oC Why do you think some towns use calcium chloride on roads in the winter versus sodium chloride? CaCl2 yields three ions while NaCl yields only two ions. Calcium chloride will work in colder weather. Calcium chloride will work better than sodium chloride. Secondly, calcium chloride doesn’t kill grass like sodium chloride.

25 What happens to the triple point?

26 Which is more effective for lowering the freezing point of water?
NaCl or CaCl 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.

27 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. If you add more solvent to a solution, the two mix together to form a more dilute solution. The same forces allowing that mixing serve to force solvent molecules from the pure solvent compartment across the membrane into the solution compartment causing the change in volume. The amount of osmotic pressure is directly related to the concentration of the solute. That is because more concentrated solutions have greater potentials for dilution.

28 Osmotic Pressure and Cells
In the figure, red blood cells are placed into saline solutions. In which case (hypertonic, isotonic, or hypotonic) does the concentration of the saline solution match that of the blood cells? In which case is the saline solution more concentrated than the blood cells? Crenation Hemolysis

29 Ideal solutions Two types of molecules are randomly distributed
Typically, molecules are similar in size and shape Intermolecular forces in pure liquids & mixture are similar Examples: benzene & toluene, hexane and heptane Ideality in solutions means complete uniformity of attractive forces

30 Ideal Solutions pA = pA◦ XA pB = pB◦ XB P solution = pA + pB
Raoult's Law States that, in an ideal solution, the partial vapor pressure of each volatile constituent is equal to the vapor pressure of the pure constituent multiplied by its mole fraction in the solution. Thus, for two constituents A and B, pA = pA◦ XA pB = pB◦ XB P solution = pA + pB

31 Real Solutions Cohesion and Attraction ?? Ideality in solutions presupposes complete uniformity of attractive forces. Many examples of solution pairs are known, however, in which the “cohesive” attraction of A for A exceeds the “adhesive” attraction existing between A and B. Similarly, the attractive forces between A and B may be greater than those between A and A or B and B. Such mixtures are real or nonideal; that is, they do not adhere to Raoult’s law Two types of deviation from Raoult’s law are recognized, negative deviation and positive deviation.

32 Negative deviation Positive deviation
When the “adhesive” attractions between molecules of different species exceed the “cohesive” attractions between like molecules, the vapor pressure of the solution is less than that expected from Raoult’s ideal solution law, and negative deviation occurs. Adhesion > Cohesion Positive deviation When the “adhesive” attractions between molecules of different species are weaker than “cohesive” attractions between like molecules, the vapor pressure of the solution is more than that expected from Raoult’s ideal solution law, and positive deviation occurs. Adhesion < Cohesion

33 Questions ! 10/31/2015


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