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Chapter 11 Properties of Solutions. Solution Composition Molarity (M) = moles solute / Liters solution Mass Percent – no units –(mass solute / mass solution)

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Presentation on theme: "Chapter 11 Properties of Solutions. Solution Composition Molarity (M) = moles solute / Liters solution Mass Percent – no units –(mass solute / mass solution)"— Presentation transcript:

1 Chapter 11 Properties of Solutions

2 Solution Composition Molarity (M) = moles solute / Liters solution Mass Percent – no units –(mass solute / mass solution) x 100 Mole Fraction – no units – decimal number χ a = (mol a / mol total ) Molality (m) = moles solute / kg solvent –Does not change with temp

3 Example - #25 p. 548 A solution is made by dissolving 25g of NaCl in enough water to make 1.00L of solution. Calculate the mass percent, molarity, molality, and mole fraction of the sodium chloride. Assume the density of the solution is 1.00g/mL

4 Solubility Likes dissolve likes –Polar dissolves polar –Nonpolar dissolves nonpolar For solids –Increased Temp usually increases solubility Gases –Increased Temp decreases solubility –Increased Pressure increases solubility Henrys Law

5 The amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the solution P=kC P is the pressure above the gas above the solution k is constant for a solution C is the concentration of the dissolved gas

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9 Implications of Gas Solubility From: _Dissolved_Oxygen.pdf

10 Vapor Pressure of Solutions A nonvolatile solute added to a solvent ALWAYS lowers the vapor pressure of the solution Fewer molecules to enter the gas phase Follows Raoults Law Called Ideal solutions

11 Raoults Law P solution = χ solvent * P solvent Where –P soluiton = Vapor Pressure of Solution –χ solvent = mole fraction of solvent –P solvent = Vapor Pressure of the solvent Since the mole fraction is always less than one the pressure of the solution is lowered

12 Example - #45 p. 549 A solution is prepared by mixing 50.0 grams of glucose C 6 H 12 O 6 with g of water. What is the vapor pressure of the solution at 25ºC? The vapor pressure of water at 25ºC is 23.8 torr.

13 More on Raoults Law Nonelectrolyes (covalent compounds) have the expected change you calculate Electrolytes (Ionic compounds) will see a bigger change in vapor pressure Ex. Ethanol lowers vapor pressure of water as expected –NaCl doubles the lowering of the vapor pressure. MgCl 2 triples

14 Deviations From Ideal When the solute and the solvent have similar polarity the vapor pressure of the solution is lower –Attraction b/t particles –Negative deviation When the solute and the solvent have dissimilar polarity the vapor pressure of the solution is higher –Positive deviation

15 Effect of Solute on Solution What effect will the lowering of the vapor pressure have on the solution? Boiling point will go up Freezing point will go down

16 Colligative Properties Properties that depend on the number of particles in solution Vapor Pressure Depression Boiling Point Elevation Freezing Point Depression Osmotic Pressure

17 Boiling Point Elevation ΔT b = Change in the boiling point Kb = Boiling point elevation constant Units of (ºC*kg/mol) –Constant for a given substance Data found in table 11.5 on page 532 –If ΔT b for salt water is 2.2ºC then the new B.P. is 102.2

18 The vant Hoff Factor i = The vant Hoff factor –Tells you how many moles of particles a solute would form if 1 mole dissolves –All covalent compounds have an i of 1 They do not ionize –i for ionic compounds equals the # of ions NaCl = 2 MgCl 2 = 3 AlCl 3 = 4

19 Freezing Point Depression ΔT f = Change in the freezing point K f = Freezing point depression constant Units of (ºC*kg/mol) –If ΔT f for salt water is 2.2ºC then the new F.P. is -2.2ºC

20 Supercooling From:

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22 Example What is the freezing point of water if 0.25 mol. of glucose is dissolved in 500mL of water? K f =1.86 ºC*kg/mol?

23 Example What is the new boiling point of water when 100. grams of NaCl is dissolved in 2.0L of water? K b =0.51 ºC*kg/mol

24 Example Ethylene Glycol (C 2 H 6 O g/mol) is placed in radiators to prevent the water from boiling. How many moles of EG must be added to 10.0L of water to make the water boil at ºC? K b =0.51 ºC*kg/mol

25 Osmosis The flow of solvent molecules into a solution through a semipermeable membrane High concentration of solvent to low concentration of solvent

26 Osmotic Pressure The Pressure required to stop osmosis Pressure required to cause reverse osmosis Π=iMRT Π = osmotic pressure (atm) i = vant Hoff factor M = Molarity R = L*atm/mol*K T = Temp in K

27 Homework P.548 #s 26,28abd,38,46,57,63,70,72


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