CHAPTER 15
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Transcript of CHAPTER 15
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CHAPTER 15CHAPTER 15
SolutionsSolutions
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SoluteSoluteA solute is the dissolved substance in a solution.
A solvent is the dissolving medium in a solution.
SolvenSolventt
Salt in salt water Sugar in soda drinks
Carbon dioxide in soda drinks
Water in salt water Water in soda
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Concentrated vs. DiluteConcentrated vs. Dilute
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Saturation of SolutionsSaturation of Solutions
A solution that contains the maximum A solution that contains the maximum amount of solute that may be dissolved amount of solute that may be dissolved under existing conditions is under existing conditions is saturatedsaturated. .
A solution that contains less solute than a A solution that contains less solute than a saturated solution under existing saturated solution under existing conditions is conditions is unsaturatedunsaturated. .
A solution that contains more dissolved A solution that contains more dissolved solute than a saturated solution under the solute than a saturated solution under the same conditions is same conditions is supersaturatedsupersaturated..
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Saturation and EquilibriumSaturation and Equilibrium
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Solubility Rules
Reference Tables
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Solubility Values
• Solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature
• The rate at which a substance dissolves does not alter the substances solubility
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Factors that Affect Solubility
• Temperature
– Solubility of solids increases with temperature
– Solubility of gases decreases with temperature
• Pressure
– has no real effect on the solubility of liquids and solids in liquid solvents
– Increasing pressure increases the solubility of gases in liquids
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Solubility Curves
• Each line represents a solute
• Higher curves mean that the solute is more soluble, lower curves are less soluble
• ABOVE the curve is SUPERsaturated, on the curve is saturated, and UNDER the curve is UNsaturated
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Solubility ChartSolubility Chart
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Solubility TrendsSolubility Trends The solubility of MOST solids increases The solubility of MOST solids increases
with temperature. with temperature.
The rate at which solids dissolve increases The rate at which solids dissolve increases with increasing surface area of the solid. with increasing surface area of the solid.
The solubility of gases decreases with The solubility of gases decreases with increases in temperature. increases in temperature.
The solubility of gases increases with the The solubility of gases increases with the pressure above the solution.pressure above the solution.
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Therefore…Therefore…Solids tend to dissolve best when:
o Heated o Stirred o Ground into small particles
Gases tend to dissolve best when:o The solution is cold
o Pressure is high
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Review Questions
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Problem 18
A physical change occurs when
– A a peach spoils
– B a bracelet turns your wrist green
– C a copper bowl tarnishes
– D a glue gun melts a glue stick
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Problem 19
What substance has a melting point of -94°C and a boiling point of 65°C?
– a. Ethanol
– b. Chlorine
– c. Hexane
– d. Methanol
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Problem 20
22.4 liters of a gas has a mass of 36.5 grams. What is the identity of the gas?
– a. Chlorine
– b. Hydrogen chloride
– c. Nitrogen
– d. Hydrogen
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Day 2
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Molarity and Dilutions
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Heat of SolutionHeat of SolutionThe Heat of Solution is the amount of heat energy absorbed (endothermic) or released (exothermic) when a specific amount of solute dissolves in a solvent.
•Endothermic: absorbs heat so it feels cool
•Exothermic: releases heat so it feels hot
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MolarityMolarity
The concentration of a solution measured in moles of solute per liter of solution.
mol of solute = M L of solution
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Example
What is the molarity of 2.5 mol KCl in 1.0L solution?
M= mol L
M= 2.5mol 1L
M= 2.5M
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Example 2
What is the molarity of 0.96g MgCl2 in 500mL of solution?
M= mol L
0.96g MgCl2 1mol MgCl2 = .01 mol MgCl295g MgCl2
M= .01 mol MgCl2.500L
M= .02M
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ExampleHow many moles of solute are contained in
15.25mL of a 2.1M solution of CaCl2?
M = mol L
# of mol = molarity x L of solution
# of mol = 2.1M (.01525L)
# of mol = .032 mol CaCl2
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Practice Problems
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Practice 1
What is the molarity of 1.35 mol H2SO4 in 245mL solution?
M= 5.51M
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Practice 2
What is the molarity 9.33g Na2S in 450 mL solution?
M= 0.27M
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Practice 3
How many moles of solute are contained in 125mL of a 0.050M
solution of Ba(OH)2?
.00625mol
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Practice 4
How many grams of solute are contained in 64.3mL of a 0.0238M
solution of KOH?
.0859g
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Practice 5
How many grams of solute are contained in 142mL of a 1.4M solution
of K2SO4?
34.6g
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Dilutions
• Because the # of moles of solute does not change during a dilution
Moles of solute in the stock solution = moles of solute after dilution
M1V1=M2V2
M1V1 is the molarity and volume of the stock solution and M2V2 is the molarity and volume of the diluted
solution
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Example
• How many milliliters of 2.55M NaOH is needed to make 125ml 0.75M NaOH?
M1V1 = M2V2
V1= M2V2
M1
V1=(.75)(125) 2.55
V1= 36.76L
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Practice Problems
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Practice 1
How would you prepare 500mL of 3 M HCl using 6 M HCl from the
stockroom?
250mL
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Practice 2
How much 12 M HCl must be used to prepare 500 ml of a 1 M HCl
solution?
41.67mL
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Homework
Molarity and Dilution Problems
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Review Questions
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Problem 21
• Which of the following substances best illustrates polar covalent bonding?
– a. HCl
– b. NaBr
– c. CsF
– d. Cl2
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Problem 22
• The methane, CH4, gas molecule exhibits what type of geometric shape?
– a. trigonal planar
– b. tetrahedral
– c. bent or V-shaped
– d. trigonal pyramidal
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Problem 23
• Which substance would have London dispersion forces as the main type of intermolecular forces of attraction?
– a. H2O
– b. F2
– c. HCl
– d. NaCl
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Problem 24
• Which of the following compounds is an exception to the octet rule?
– a.BH3
– b.CH4
– c.NH3
– d.H2O