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Chapter 15
Table of Contents
2
15.1 Solubility
15.2 Solution Composition: An Introduction
15.3 Solution Composition: Mass Percent
15.4 Solution Composition: Molarity
15.5 Dilution
Chapter 15
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3
What is a Solution?
• Solution – homogeneous mixture Solvent – substance present in largest
amount Solutes – other substances in the solution Aqueous solution – solution with water as the
solvent
Section 15.1
Solubility
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Copyright © Cengage Learning. All rights reserved 5
• Ionic substances breakup into individual cations and anions.
Solubility of Ionic Substances
Section 15.1
Solubility
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Copyright © Cengage Learning. All rights reserved 6
• Polar water molecules interact with the positive and negative ions of a salt.
Solubility of Ionic Substances
Section 15.1
Solubility
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Copyright © Cengage Learning. All rights reserved 7
• Ethanol is soluble in water because of the polar OH bond.
Solubility of Polar Substances
Section 15.1
Solubility
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8
• Why is solid sugar soluble in water?
Solubility of Polar Substances
• Why is isopropyl alcohol soluble in water?
Oδ-
Hδ+ Hδ+
Section 15.1
Solubility
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9
• Why is blue food coloring soluble in water?
Solubility of Polar Substances
Blue food dye mixes with alcohol and water unless a dissolved salt dominates the water as a solvent.
Section 15.1
Solubility
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Copyright © Cengage Learning. All rights reserved 10
• Nonpolar oil does not interact with polar water.• Water-water hydrogen bonds keep the water
from mixing with the nonpolar molecules.
Substances Insoluble in Water
Section 15.1
Solubility
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11
• A “hole” must be made in the water structure for each solute particle.
• The lost water-water interactions must be replaced by water-solute interactions.
• “like dissolves like”
How Substances Dissolve
Section 15.1
Solubility
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Copyright © Cengage Learning. All rights reserved 12
Concept Check
Which of the following solutes will generally not dissolve in the specified solvent? Choose the best answer. (Assume all of the compounds are in the liquid state.)
a) CCl4 mixed with water (H2O)
b) NH3 mixed with water (H2O)
c) CH3OH mixed with water (H2O)
d) N2 mixed with methane (CH4)
Section 15.1
Solubility
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Copyright © Cengage Learning. All rights reserved 13
Factors that affect Solubility
• Molecular structure-like dissolves like– ionic nature– polarity
• Temperature– Increased temperatures increase solubility of solids
dissolved in liquids.– Increased temperatures decrease solubility of gasses
dissolved in liquids.• Pressure
– Increased pressures increase solubility of gasses dissolved in liquids.
Section 15.2
Solution Composition: An Introduction
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15
• The solubility of a solute is limited. Saturated solution – contains as much
solute as will dissolve at that temperature.
Unsaturated solution – has not reached the limit of solute that will dissolve.
Section 15.2
Solution Composition: An Introduction
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16
• Supersaturated solution – occurs when a solution is saturated at an elevated temperature and then allowed to cool but all of the solid remains dissolved. Contains more dissolved solid than a
saturated solution at that temperature. Unstable – adding a crystal causes
precipitation.
http://axiomsun.com/home/video/supercooled_water.html
http://www.youtube.com/watch?v=HnSg2cl09PI
http://www.youtube.com/watch?v=nvHrXr5Jajg
http://www.youtube.com/watch?v=OjeFliFZQ8A&NR=1
Section 15.2
Solution Composition: An Introduction
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Copyright © Cengage Learning. All rights reserved 17
• Solutions are mixtures. • Amounts of substances can vary in different
solutions. Specify the amounts of solvent and
solutes. Qualitative measures of concentration
concentrated – relatively large amount of solute
dilute – relatively small amount of solute
Section 15.3
Solution Composition: Mass Percent
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Copyright © Cengage Learning. All rights reserved 18
mass of soluteMass percent = 100%
mass of solution
grams of soluteMass percent = 100%
grams of solute + grams of solvent
Section 15.3
Solution Composition: Mass Percent
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Copyright © Cengage Learning. All rights reserved 19
Exercise
What is the percent-by-mass concentration of glucose in a solution made my dissolving 5.5 g of glucose in 78.2 g of water?
6.6% [5.5 g / (5.5 g + 78.2 g)] × 100 = 6.6% glucose
Section 15.4
Solution Composition: Molarity
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Copyright © Cengage Learning. All rights reserved 20
• Molarity (M) = moles of solute per volume of solution in liters:
moles of solute = Molarity = liters of solution
M
6 moles of HCl3 HCl = 2 liters of solution
M
Section 15.4
Solution Composition: Molarity
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21
Exercise
You have 1.00 mol of sugar in 125.0 mL of solution. Calculate the concentration in units of molarity.
8.00 M
1.00 mol / (125.0 / 1000) = 8.00 M
Section 15.4
Solution Composition: Molarity
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Copyright © Cengage Learning. All rights reserved 22
Exercise
A 500.0-g sample of potassium phosphate is dissolved in enough water to make 1.50 L of solution. What is the molarity of the solution?
1.57 M
500.0 g is equivalent to 2.355 mol K3PO4 (500.0 g / 212.27 g/mol). The molarity is therefore 1.57 M (2.355 mol/1.50 L).
Section 15.4
Solution Composition: Molarity
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23
Exercise
You have a 10.0 M sugar solution. What volume of this solution do you need to have 2.00 mol of sugar?
0.200 L 2.00 mol / 10.0 M = 0.200 L
Section 15.4
Solution Composition: Molarity
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24
Exercise
Consider separate solutions of NaOH and KCl made by dissolving 100.0 g of each solute in 250.0 mL of solution. Calculate the concentration of each solution in units of molarity.
10.01 M NaOH[100.0 g NaOH / 39.998 g/mol] / [250.0 / 1000] = 10.01 M NaOH
5.366 M KCl[100.0 g KCl / 74.55 g/mol] / [250.0 / 1000] = 5.366 M KCl
Section 15.4
Solution Composition: Molarity
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Copyright © Cengage Learning. All rights reserved 25
Concept Check
You have two HCl solutions, labeled Solution A and Solution B. Solution A has a greater concentration than Solution B. Which of the following statements are true?
a) If you have equal volumes of both solutions, Solution B must contain more moles of HCl.
b) If you have equal moles of HCl in both solutions, Solution B must have a greater volume.c) To obtain equal concentrations of both solutions, you must add a certain amount of water to
Solution B.d) Adding more moles of HCl to both solutions will make them less concentrated.
Section 15.4
Solution Composition: Molarity
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26
• For a 0.25 M CaCl2 solution:
CaCl2 → Ca2+ + 2Cl–
Ca2+: 1 × 0.25 M = 0.25 M Ca2+
Cl–: 2 × 0.25 M = 0.50 M Cl–.
Concentration of Ions
Section 15.4
Solution Composition: Molarity
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Copyright © Cengage Learning. All rights reserved 27
Concept Check
Which of the following solutions containsthe greatest number of ions?
a) 400.0 mL of 0.10 M NaCl.
b) 300.0 mL of 0.10 M CaCl2.
c) 200.0 mL of 0.10 M FeCl3.
d) 800.0 mL of 0.10 M sucrose.
Section 15.4
Solution Composition: Molarity
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Copyright © Cengage Learning. All rights reserved 28
• Where are we going? To find the solution that contains the greatest
number of moles of ions.
• How do we get there? Draw molecular level pictures showing each
solution. Think about relative numbers of ions. How many moles of each ion are in each
solution?
Let’s Think About It
Section 15.4
Solution Composition: Molarity
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29
• The solution with the greatest number of ions is not necessarily the one in which: the volume of the solution is the
largest. the formula unit has the greatest
number of ions.
Notice
Section 15.4
Solution Composition: Molarity
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30
• A solution whose concentration is accurately known.
Standard Solution
Section 15.4
Solution Composition: Molarity
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Copyright © Cengage Learning. All rights reserved 31
• Weigh out a sample of solute.• Transfer to a volumetric flask.• Add enough solvent to mark on flask.
To Make a Standard Solution
Section 15.5
Dilution
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32
• The process of adding water to a concentrated or stock solution to achieve the molarity desired for a particular solution.
• Dilution with water does not alter the numbers of moles of solute present.
• Moles of solute before dilution = moles of solute after dilution
M1V1 = M2V2
Section 15.5
Dilution
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Copyright © Cengage Learning. All rights reserved 33
• Transfer a measured amount of original solution to a flask containing some water.
• Add water to the flask to the mark (with swirling) and mix by inverting the flask.
Diluting a Solution
Section 15.5
Dilution
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Copyright © Cengage Learning. All rights reserved 34
Concept Check
A 0.50 M solution of sodium chloride in an open beaker sits on a lab bench. Which of the following would decrease the concentration of the salt solution?
a) Add water to the solution.
b) Pour some of the solution down the sink drain.
c) Add more sodium chloride to the solution.
d) Let the solution sit out in the open air for a couple of days.
e) At least two of the above would decrease the concentration of the salt solution.
Section 15.5
Dilution
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35
Exercise
What is the minimum volume of a 2.00 M NaOH solution needed to make 150.0 mL of a 0.800 M NaOH solution?
60.0 mL
M1V1 = M2V2
(2.00 M)(V1) = (0.800 M)(150.0 mL)
Section 15.5
Dilution
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37
15.6 Stoichiometry of Solution Reactions
15.7 Neutralization Reactions
15.8 Solution Composition: Normality
Section 15.6
Stoichiometry of Solution Reactions
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Copyright © Cengage Learning. All rights reserved 38
1. Write the balanced equation for the reaction. For reactions involving ions, it is best to write the net ionic equation.
2. Calculate the moles of reactants.
3. Determine which reactant is limiting.
4. Calculate the moles of other reactants or products, as required.
5. Convert to grams or other units, if required.
Steps for Solving Stoichiometric Problems Involving Solutions
Section 15.6
Stoichiometry of Solution Reactions
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Copyright © Cengage Learning. All rights reserved 39
Concept Check (Part I)
10.0 mL of a 0.30 M sodium phosphate solution reacts with 20.0 mL of a 0.20 M lead(II) nitrate solution (assume no volume change).
What precipitate will form?
lead(II) phosphate, Pb3(PO4)2
What mass of precipitate will form?
0.91 g Pb3(PO4)2 see next 2 slides
Section 15.6
Stoichiometry of Solution Reactions
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Copyright © Cengage Learning. All rights reserved 40
• Where are we going? To find the mass of solid Pb3(PO4)2 formed.
• How do we get there? What are the ions present in the combined solution? What is the balanced net ionic equation for the
reaction? What are the moles of reactants present in the
solution? Which reactant is limiting? What moles of Pb3(PO4)2 will be formed?
What mass of Pb3(PO4)2 will be formed?
Let’s Think About It
Section 15.6
Stoichiometry of Solution Reactions
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Copyright © Cengage Learning. All rights reserved 41
0.0100L P(0.30 moles P/L)(1 mole LP/2mole P) (812g LP/mole) = 1.1g LP
0.0200L Lead(0.20 moles Lead/L)(1 mole LP/3mole L)(812g LP/mole) = 0.91g LP
2PO4-3 + 3Pb2+ Pb3(PO4)2(s)
Section 15.6
Stoichiometry of Solution Reactions
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42
Concept Check (Part II)
10.0 mL of a 0.30 M sodium phosphate solution reacts with 20.0 mL of a 0.20 M lead(II) nitrate solution (assume no volume change).
What is the concentration of nitrate ions left in solution after the reaction is complete?
0.27 M see next two slides
Section 15.6
Stoichiometry of Solution Reactions
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Copyright © Cengage Learning. All rights reserved 43
• Where are we going? To find the concentration of nitrate ions left in
solution after the reaction is complete.
• How do we get there? What are the moles of nitrate ions present in the
combined solution? What is the total volume of the combined
solution?
Let’s Think About It
Section 15.6
Stoichiometry of Solution Reactions
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Copyright © Cengage Learning. All rights reserved 44
0.0200L LN(0.20 moles LN/L)(2 mole N/1mole LN)= 0.0080 moles Nitrate ion
0.0080moles N/(0.0100L + 0.0200L) = 0.27 M Nitrate
2NO3- + Pb2+ Pb(NO3)2(aq)
Section 15.6
Stoichiometry of Solution Reactions
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45
Concept Check (Part III)
10.0 mL of a 0.30 M sodium phosphate solution reacts with 20.0 mL of a 0.20 M lead(II) nitrate solution (assume no volume change).
What is the concentration of phosphate ions left in solution after the reaction is complete?
0.02 M see next two slides
Section 15.6
Stoichiometry of Solution Reactions
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Copyright © Cengage Learning. All rights reserved 46
• Where are we going? To find the concentration of phosphate ions left in
solution after the reaction is complete.
• How do we get there? What are the moles of phosphate ions present in
the solution at the start of the reaction? How many moles of phosphate ions were used
up in the reaction to make the solid Pb3(PO4)2?
How many moles of phosphate ions are left over after the reaction is complete?
What is the total volume of the combined solution?
Let’s Think About It
Section 15.6
Stoichiometry of Solution Reactions
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Copyright © Cengage Learning. All rights reserved 47
(1.1g LP-0.91g LP)(1mole LP/812g)(2mole P/1mole LP)/ (0.0100L+0.0200L) = 0.02 M Phosphate Ion
2PO4-3 + 3Pb2+ Pb3(PO4)2(s)
Section 15.7
Neutralization Reactions
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Copyright © Cengage Learning. All rights reserved 48
• An acid-base reaction is called a neutralization reaction.
• Steps to solve these problems are the same as before.
• For a strong acid and base reaction:
H+(aq) + OH–(aq) H2O(l)
Section 15.7
Neutralization Reactions
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Copyright © Cengage Learning. All rights reserved 49
Concept Check
For the titration of sulfuric acid (H2SO4) with sodium hydroxide (NaOH), how many moles of sodium hydroxide would be required to react with 1.00 L of 0.500 M sulfuric acid?
1.00 mol NaOH see next 2 slides
Section 15.7
Neutralization Reactions
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Copyright © Cengage Learning. All rights reserved 50
• Where are we going? To find the moles of NaOH required for the
reaction.
• How do we get there? What are the ions present in the combined
solution? What is the reaction? What is the balanced net ionic equation for the
reaction? What are the moles of H+ present in the solution? How much OH– is required to react with all of the
H+ present?
Let’s Think About It
Section 15.7
Neutralization Reactions
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Copyright © Cengage Learning. All rights reserved 51
H2SO4 + 2NaOH Na2SO4 + 2H2O
1.00L SA(0.500 moles SA/L)(2 mole SH/1mole SA)= 1.00 mol NaOH
Section 15.7
Neutralization Reactions
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Copyright © Cengage Learning. All rights reserved 52
HA + NaOH Salt + H2O
If I use 8.34 ml of a 0.1562 M solution of NaOH to titrate or neutralize 10.12 ml of a monoprotic acid
(one H), what is the concentration of the acid?
0.00834 L SH (0.1562mol SH/L)(1 mole HA/1 mole SH)
/0.01012L HA = 0.129 M HA
Section 15.8
Solution Composition: Normality
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Copyright © Cengage Learning. All rights reserved 53
• One equivalent of acid – amount of acid that furnishes 1 mol of H+ ions.
• One equivalent of base – amount of base that furnishes 1 mol of OH ions
• Equivalent weight – mass in grams of 1 equivalent of acid or base.
Unit of Concentration
Section 15.8
Solution Composition: Normality
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Copyright © Cengage Learning. All rights reserved 54
Section 15.8
Solution Composition: Normality
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Copyright © Cengage Learning. All rights reserved 55
Section 15.8
Solution Composition: Normality
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Copyright © Cengage Learning. All rights reserved 56
• To find number of equivalents:
number of equivalents equivalents equivNormality = = = =
1 liter of solution liter LN
equiv V = L = equiv
LN
Section 15.8
Solution Composition: Normality
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Copyright © Cengage Learning. All rights reserved 57
Concept Check
If Ba(OH)2 is used as a base, how many equivalents of Ba(OH)2 are there in 4 mol Ba(OH)2?
a) 2b) 4c) 8d) 16
Section 15.8
Solution Composition: Normality
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58
Colligative Properties (not in textbook)
• A property that does not depend on the identity of a solute in solution
• Vary only with the number of solute particles present in a specific quantity of solvent
• 4 colligative properties:– Osmotic pressure– Vapor pressure lowering– Boiling point elevation– Freezing point depression
11-
Section 15.8
Solution Composition: Normality
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59
Osmotic Pressure
• Osmosis– A process in which solvent molecules diffuse through a
barrier that does not allow the passage of solute particles• The barrier is called a semipermeable membrane.
– A membrane that allows the passage of some substances but not others
• Osmotic Pressure– Pressure that can be exerted on the solution to prevent
osmosis
11-
Section 15.8
Solution Composition: Normality
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60
Osmotic Pressure
• Reverse Osmosis- Ultra Filtration– A process in which pressure is applied to reverse the osmosis
flow. – A form of molecular filtration used to remove salt from water.
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Section 15.8
Solution Composition: Normality
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62
Vapor Pressure Lowering
Solutes come in 2 forms:
• Volatile
– Solutes that readily form a gas• Nonvolatile
– Solutes that DO NOT
readily form a gas• Generally, the addition of a
solute lowers the vapor
pressure of a solution when
compared to the
pure solvent.
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Section 15.8
Solution Composition: Normality
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Solutions under sealed container to start with.
Solutions under sealed container at later time.
Vapor Pressure Lowering
Section 15.8
Solution Composition: Normality
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Supercritical Extraction
•Removal of caffeine from coffee using supercritical CO2 or natural effervescence .
•Removal of oils (fats) from potato chips.
•Dry Cleaning Cloths
31.1 °C 72.9 atm
Section 15.8
Solution Composition: Normality
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66
Boiling Point Elevation
• The addition of solute affects the boiling point because it affects the vapor pressure.
• The boiling point is raised with the addition of solute in comparison to the pure solvent.
• An equation that gives the increase in boiling point:
∆Tb = Kbm
Where ∆Tb is the increase in temperature from the pure solvent’s boiling point, Kb is the boiling point constant, which is characteristic of a particular solvent, and m is the molality (moles of solute per kg of solvent)
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Section 15.8
Solution Composition: Normality
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67
Freezing Point Depression
• The freezing point is lowered with the addition of solute in comparison to the pure solvent.
• An equation that gives the decrease in freezing point:
∆Tf = KfmWhere ∆Tf is the decrease in temperature from the pure solvent’s freezing point, Kf is the freezing point constant, which is characteristic of a particular solvent, and m is the molality (moles of solute per kg of solvent)
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Section 15.8
Solution Composition: Normality
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68
Examples of Colligative Properties
Antifreeze lowers the freezing point of your radiator fluid and raises the boiling point.
Salting roads melts the ice.
Section 15.8
Solution Composition: Normality
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69
Example of Freezing Point Depression
Making Ice Cream
You must add salt so as to
lower the freezing point of
the ice water cold enough to freeze the ice
cream.
Section 15.8
Solution Composition: Normality
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70
ΔTf = Kf mol solute/Kg solvent = 1.858 (78)/5.0= 29oC
0.0oC – 29oC = - 29oC freezing point
Calculations of Freezing Point Lowering and Boiling Point Elevation
What will be the coldest temperature of an ice water solution with 5.0 lbs of salt in 3.0 gallon container with about 5.0 Kg of water? What will be the boiling Point?
5.0 lbs NaCl(454g/lb)(1mole NaCl/58 g) = 39 moles NaCl
ΔTb = Kb mol solute/Kg solvent = 0.52 (78)/5.0= 8.1oC
100.00oC + 8.1oC = 108.1oC boiling point
39 moles NaCl x 2 (two particles or ions are formed) = 78
Section 15.8
Solution Composition: Normality
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71
Colligative Properties and Strong Electrolytes
• Strong electrolytes dissociate most of the time into their constituent ions.
• Therefore, the number of particles (in this case ions) increases with the number of ions.
• Colligative properties are proportional to number of particles in solution.
• Example:
MgCl2(s) Mg2+(aq) + 2 Cl-(aq)In this case the number of particles increases to 3 particles. Therefore, we would multiply the colligative property amount by 3.
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Section 15.8
Solution Composition: Normality
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72
Practice – Strong vs. Weak Electrolytes
• Which of the following aqueous solutions is expected to have the lowest freezing point?
– 0.5 m CH3CH2OH
– 0.5 m Ca(NO3)2
– 0.5 m KBr
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Forms 1 particle per molecule or formula unit: 1 x 0.5 m particles = 0.5 m particles
Forms 3 particle per molecule or formula unit: 3 x 0.5 m particles = 1.5 m particles
Forms 2 particle per molecule or formula unit: 2 x 0.5 m particles = 1.0 m particles
Thus Ca(NO3)2 should the greatest freezing point lowering or the lowest freezing point.