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Properties of Solutions: Ways of Expressing Concentrations Weight percentage = mass of component in solution total mass of solution Parts per million (ppm)

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Presentation on theme: "Properties of Solutions: Ways of Expressing Concentrations Weight percentage = mass of component in solution total mass of solution Parts per million (ppm)"— Presentation transcript:

1 Properties of Solutions: Ways of Expressing Concentrations Weight percentage = mass of component in solution total mass of solution Parts per million (ppm) = mass of component in solution total mass of solution A solution is made containing 6.9 g NaHCO 3 per 100 g water. What is the weight percentage of solute in the solution? A 2.5 g sample of ground water was found to contain 5.4 micrograms of Zn 2+. What is the concentration of Zn 2+ in ppm 6.9g g x 100 = 6.5% x 100 x x g x 10 6 ppm = Wt % of component = = 2.2ppm

2 Mole fraction, Molarity, and Molality Mole fraction of a component = Moles component Total moles of all components Calculate the mole fraction of HCl in a solution of HCl containing 36% HCl by weight. 36 g HCl 1 mole HCl 36.5 g HCl = 0.99 mol HCl 64 g H 2 O 1 mole H 2 O 18 g H 2 O = 3.6 mol H 2 O X HCl = Mole HCl Moles HCl + H 2 O = 0.99 mol 4.6 mol = 0.22

3 Mole fraction, Molarity, and Molality Molarity = Moles of solute Liters of solution What is the molarity of an ascorbic acid solution (C 6 H 8 O 6 ) prepared by dissolving 1.80 grams in enough water to make 125 mL of solution. How many milliliters of this solution contain mol ascorbic acid g C 6 H 8 O 6 1 mol C 6 H 8 O g C 6 H 8 O 6 = mol C 6 H 8 O 6 Molarity = mol C 6 H 8 O L soln = M

4 Mole fraction, Molarity, and Molality Molality = moles of solute Kg of solvent What is the molality of a solution made by dissolving 5.0 g of toluene (C 7 H 8 ) in 25 g of benzene (C 6 H 6 )? 5.0 g C 7 H 8 1 mol C 7 H 8 92 g C 7 H 8 = mol C 7 H 8 Molality = mol C 7 H kg C 6 H 6 = 2.2 m

5 Properties of Solutions: The Solution Process Na + Cl Na + Solvation or hydration Na + Cl - Na + Cl -

6 Properties of Solutions: The Solution Process Energy Changes and Solution Formation H soln = H 1 + H 2 + H 3 Solute-solute interactions Solvent-solvent interactions Solute-solvent interactions

7 Properties of Solutions: The Solution Process Energy Changes and Solution Formation The overall change in enthalpy can be exo- or endothermic NaOH: H soln = NH 4 OH: H soln = 26.4 This explains why like dissolves like

8 Properties of Solutions: Solution Formation, Spontaneity and Disorder…WHY DOES THIS STUFF DISSOLVE? bp = 77 bp = 69 London dispersion forces Little energy is exchanged

9 Properties of Solutions: Solution Formation, Spontaneity and Disorder…WHY DOES THIS STUFF DISSOLVE? Processes in which the energy content of the system decreases tend to occur spontaneously. Processes in which the disorder of the system increases tend to occur spontaneously When molecules of different types are brought together, an increase in disorder occurs spontaneously unless the molecules are restrained sufficiently by strong intermolecular forces. Salt does not dissolve in gasoline because strong forces are holding the Na + and Cl - ions together and the intermolecular forces associated with nonpolar substances is not sufficient to dislodge them.

10 Properties of Solutions: Saturated Solutions and Solubilityc As solid solute begins to dissolve in a solvent, the concentrations of solute particles in solution increases, so the chances of their colliding with the surface of the solid increases. This may lead to crystallization. Solute + Solvent Solution dissolve crystallize Saturated: a solution with undissolved solute Supersaturated: a solution which contains a greater amount of solute than needed to form a saturated solution

11 Properties of Solutions: Factors Affecting Solubility As a rule, solubility increases with increasing molecular mass Polar liquids tend to dissolve in polar solvents. If the dissolve they are miscible. If they do not dissolve they are immiscible

12 Properties of Solutions: Factors Affecting Solubility Hydrogen-boning interactions between solute and solvent may lead to high solubility Ethanol and ethanol Ethanol and water Because of H-bonding, solute-solute, solvent-solvent, and solute-solvent interactions are not appreciably different. There is no significant change in the environment

13 However, the numbers carbon atoms in an alcohol does effect it solubility in water. Properties of Solutions: Factors Affecting Solubility As the length of the chain increases, the OH groups decrease leading to a decrease in solubility

14 Glocuse has 5-OH groups on a six carbon framework which makes the molecule fairly soluble in water Properties of Solutions: Factors Affecting Solubility Substances with similar intermolecular attractive forces tend to be soluble in one another….LIKE DISSOLVES LIKE

15 Properties of Solutions: Factors Affecting Solubility Substances with similar intermolecular attractive forces tend to be soluble in one another….LIKE DISSOLVES LIKE Predict whether each of the following substances is more likely to dissolve in carbon tetrachloride or water: C 7 H 16. NaHCO 3, HCl

16 Pressure Effects Pressure Effects The solubility of a gas in any solvent is increased as the pressure of the gas over the solvent increases By contrast the solubility of solids and liquids are not appreciable affected by pressure.

17 The relationship between pressure and solubility is expressed by Henrys Law: C g = kP g where C g is the solubility of the gas in the solution phase, P g is the partial pressure of the gas over the solution, and k is a Henrys law constant which differs from one solute-solvent pair to another. For example the solubility of N 2 gas in water at 25 ° C and 0.78 atm. is 5.3 x M k = 5.3 x M/0.78 = 6.8 x mol/l-atm. Assume that the partial pressure of the N 2 is doubled, Henrys law, C g = kP g predicts that the solubility will also double. C g = kP g C g = (6.8 x mol/l-atm)(1.56 atm) C g =

18 Temperature Effects In general, the solubility of gases decreases as temperature increases

19 Temperature Effects In general, the solubility of of ionic compounds, solids, normally increases as the temperature increases.

20 Colligative Properties The increase or decrease of of the concentrations and not the kinds of particles in solutions can effect certain physical properties of solutions Freezing point depression of a solution Boiling point elevation of a solution vapor pressure; Raoults Law Osmotic pressure Colligative means depending upon the collection; colligative properties depend upon the collective effect of the number of solute particles

21 Colligative Properties Lowering the Vapor Pressure: TRY EXPLAINING THIS ONE!!

22 Lowering the Vapor Pressure: Explaining How it is Done!! A non-volatile solute added to a solvent reduces the capacity of the solvent molecules in the liquid phase to move into the gas phase The extent to which a nonvolatile solute lowers the vapor pressure is proportional to the concentration

23 Raoults Law: Calculating the vapor pressure of a solution based upon the amount of solute being added to the solution. solvent P A = X A P A ° Where P A is the vapor pressure of the solution, X A is the mole fraction of solvent, and P° A is the vapor pressure of the pure solvent

24 4 Colligative Properties are the first evidence that salts break up into ions. 4 X a = Mole of solvent i Moles of solvent + moles of solute x i If 10g of MgCl 2 is added to 100ml of H 2 O at 23ºC, what would be the vapor pressure. The vapor pressure for water at this temperature is torr.

25 What is the vapor pressure of a solution made with 1 mol of Benzene and 2 mol of toluene at 20ºC and the mole fraction of the vapor? Benzene = 75 torr and Toluene = 22 torr P A = X A P° A + P B = X B P° B

26 Properties of Solutions:Boiling Point Elevation and Freezing Point Depression

27 Because nonvolatile solutes lower the vapor pressure of a solution, a higher temperature is required to cause the solution to boil. Because the vapor pressure of the solution is lower than that of the solvent at all temps, in accordance to Raoults Law, the higher temperature is required to attain a vapor pressure of 1 atm. T b = K b m, where T b is directly proportional to the number of solute particles per moles of solvent molecules, and K b is called the molal boiling-point-elevation constant For example, the K b of water is 0.52 °C/m; therefore a 1m solution of sucrose or any other aqueous solution that is 1m in nonvolatile solute particles will boil at a temperature of 0.52°C higher than pure water. Boiling Point Elevation and Freezing Point Depression

28 The freezing point corresponds to the temperature at which the vapor pressures of the solid and liquid phases are the same. The freezing point of a solution is lowered because the solute is not normally soluble in the solid phase of the solvent If the solute is nonvolatile, the vapor pressure of the solution is reduced in proportion to the mole fraction of solute. T f = K f m, where T f is directly proportional to the number of solute particles per moles of solvent molecules, and K f is called the molal-freezing-point-depression constant For example, the K f of water is 1.86 °C/m; therefore a 0.5 m solution of NaCl or any other aqueous solution that is 1m in nonvolatile solute particles will freeze at a temperature of 1.86 °C lower than pure water.

29 Calculate the freezing point and the boiling point of a solution of 100 g of ethylene glycol (C 2 H 6 O 2 ), antifreeze in 900 g of H 2 O. m = Moles C 2 H 6 O 2 Kilograms H 2 O 100 g C 2 H 6 O kg H 2 O 1 mol C 2 H 6 O g C 2 H 6 O 2 = 1.79 m T f = K f m = 1.86 °C m (1.79 m ) = 3.33 °C Therefore freezing point = °C = T b = K b m =.52 °C m (1.79 m ) = °C

30 Adrenaline is the hormone that triggers the release of extra glucose molecules in times of stress or emergency. A solution of 0.64 g of adrenaline in 36.0 g of CCl 4 elevates the boiling pt. by 0.49ºC. What is the molar mass? 4 ΔT b = K b m K B for adrenaline is = 3.63 (.64gmole ) xg.036kg

31 Properties of Solutions:Osmosis The net movement of solvent is always toward the more concentrated solution The pressure required to prevent osmosis is called the osmotic pressure,, of the solution, where = MRT

32 Hypertonic Solution Hypotonic Solution Properties of Solutions:Osmosis

33 Sample problem: The average osmotic pressure of blood is 7.7 atm. At 25°C. What concentration of glucose (C 6 H 12 O 6 ) would be isotonic with blood?

34 Lysozyme is an enzyme that breaks bacterial cell walls. a solution containing g of this enzyme in 210 mL of solution has an osmotic pressure of torr at 25ºC. What is the molar mass of Lysozyme? π = MRT.953 =.150g mole xg.21L

35 Properties of Solutions:Colloids Suspensions that are the dividing Line Between Solutions and Heterogeneous Mixtures Tyndell effect: a scattering of light by colloidal particles

36 Properties of Solutions:Colloids Hydrophilic and Hydrophobic Colloids The most important colloids are those in which the dispersing medium is water Hydrophilic colloids are kept in suspension by interaction with surrounding water molecules

37 Properties of Solutions:Colloids Hydrophilic and Hydrophobic Colloids The most important colloids are those in which the dispersing medium is water Hydrophobic colloids can be stabilized in water by the adsorption of ions onto their surface

38 Properties of Solutions:Colloids Hydrophilic and Hydrophobic Colloids The most important colloids are those in which the dispersing medium is water

39 P a = X a P a º X a = moles of solvent moles of solvent + moles of solute x i ΔT b = K b m i ΔT f = K f m i π = MRTi


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