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Ch.16 sections 1 and 2 notes with notations
1
April 12, 2018
Mar 2611:47 AM
CHAPTER 16 Solutions
Mar 2611:47 AM
16.1 Solution Formation• Solutions can be either solids, liquids, or gases
• Solutions are homogeneous mixtures that are grouped according to physical state. (mixtures = no bonding)
• The nature of solvent and solute affects whether a substance will dissolve.
Mar 2611:45 AM
• Solvation is a surface phenomenon!• Water dissolving NaCl.• Water can only dissolve ions they touch
Solvation = Dissolving
O
H H
Na+
Cl
Mar 2611:47 AM
Solute is dissolved
Na+Na+
Na+
Na+Na+
ClCl
ClCl
Cl
Mar 2611:47 AM
What determines how fast solutes dissolve?
1. amount of surface area 2. force of collisions with solvent3. frequency of collisions with solvent
Mar 2611:47 AM
3 factors increase the rate of solvation:
• Agitation• Temperature• Particle Size
These increase the collisions between solvent and solute
Ch.16 sections 1 and 2 notes with notations
2
April 12, 2018
Mar 2611:48 AM
Agitation
• solvent is brought into contact with the solute more frequently with greater force.
• Shaking and stirring
Mar 2611:49 AM
Temperature
• increases the force and frequency of solvent and solute
• Heat makes particles move faster
Mar 2611:49 AM
Particle Size• Powder has less surface, but very little volume
• Crystals have more surface, but a larege volume
• Powder has a greater surface area:volume ratio
Mar 2611:50 AM
Solubility• A saturated solution contains the maximum amount of
solute for a given amount of solvent at a constant temperature.
• How much solute can a given amount of solvent hold...
Apr 1011:58 AM Mar 2611:51 AM
• The solubility of a substance is the amount of substance that dissolves in a given quantity of a solvent at a given temperature to produce a saturated solution.
• Solubility changes if temperature changes.
Ch.16 sections 1 and 2 notes with notations
3
April 12, 2018
Mar 267:54 AM
SolubilityMaximum amount of solute dissolved in 100mL of solvent at a given temperature.
20°C
34.2g
KCl
30°C
37.2g
KCl
40°C
40.1g
KCl
Mar 2611:51 AM
36.2 g NaCl
100g H2Oat 25 °C
Solubility Example
• 36.2 grams of NaCl in 100 grams of water @ 25 °C.
Mar 2611:52 AM
Important!!!!!
• Solubility is generally expressed in grams of solute per 100 g of solvent.
• A solution that contains less solute than a saturated solution is unsaturated
100g = 100mL
grams of solute
100g H2Oat 20 °C
Mar 2611:53 AM
Dynamic Equilibrium in a saturated solution.
• Rate of Solvation = Rate of Desolvation• Dissolving = Crystallization• Particles move from solid to solvated state and back to
solid again.
Mar 2611:53 AM
Factors Affecting Solubility• The solubility of liquids and solids increases with temperature
• The solubility of gases decreases with temperature
Apr 97:37 AM
Supersaturated Solutions20°C
Saturated
20°C
Supersaturated
30°C
Saturated
125g
NaCl125g
NaCl
100g
NaCl
Ch.16 sections 1 and 2 notes with notations
4
April 12, 2018
Mar 262:43 PM
Supersaturated Solution
• Crystallization in a supersaturated solution can be initiated if a very small crystal, called a seed crystal, of the solute is added
Removing solute from a supersaturated solution
Apr 1112:06 PM
http://www.teachertube.com/viewVideo.php?video_id=86887
http://www.metacafe.com/watch/404010/rapid_crystallization_supersaturated_solution_demo/
Seed Crystal Video
Mar 262:44 PM
• Two liquids are said to be miscible if they dissolve in each other. (Polar & Polar or Nonpolar & Nonpolar)
• Liquids that are insoluble in one another are immiscible (NonPolar & Polar)
Liquids and Liquids
Mar 262:44 PM
• The solubilities of gases are greater in cold water than in hot water
• Hotter water has higher vapor pressure, which allows gas to escape
• The components of air become less soluble as the temperature of the water rises.
Mar 262:44 PM
Thermal Pollution• Industrial plants remove cold water and dump hot water back into the lake.
• This increases the temperature of the water, decreasing the dissolved O2.
• Warm vs. Cold Soda can
Mar 262:59 PM
Henry’s Law• at a given temperature the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid
• In other words, as the pressure of the gas above the liquid increases, the solubility of the gas increases
S1 S2
P1 P2
Ch.16 sections 1 and 2 notes with notations
5
April 12, 2018
Mar 263:04 PM
Example
A gas has a solubility in water of 10.5 g/L at 15 °C and 455 kPa of pressure. What is the solubility of the gas in water at 15 °C and 615 kPa of pressure?
10.5 g/L
455kPa 615kPa
Mar 263:04 PM
16.2 Concentrations of Solutions• The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent.
• The unit for concentration is Molarity
Mar 262:47 PM
Concentration= amount of solute dissolved in a solvent.
Dilute solutions have a small amount of solute.
Concentrated solutions have a large amount of solute.
Mar 262:46 PM
Molarity (M)Moles of soluteLiters of solution
n
v M
n = moles
v = volume
M = molarity
Mar 262:46 PM
Key Concept!Is it possible to have 1mL of 5.0M solution?
If you poured 5.0M HCl into 3 different size containers, would the molarity in each container change?
Apr 1112:48 PM
200mL
2.0 M HCl
300mL
2.0 M HCl
Are the substances different because they have different amounts in them?
Does each flask have 2 moles of HCl dissolved?
Ch.16 sections 1 and 2 notes with notations
6
April 12, 2018
Apr 1112:48 PM
2.0moles
1.0L 0.2L
2.0moles
1.0L 0.3L
200mL
2.0 M HCl
300mL
2.0 M HCl
Which flask has more moles of HCl dissolved?
Mar 2810:55 AM
4 moles
0.5L
Example #1
What is the molarity of NaCl in sea water if it contains 4 moles of NaCl per 500mL?
Mar 2810:54 AM
Example #2
What is the molarity of NaCl in sea water if it contains 20.5 g of NaCl per 750mL?
.350 moles
0.75L
20.5g NaCl 1 mole
58.5g
Mar 2810:54 AM
Example #3How many moles of NaCl are dissolved in 100.0 mL of a 5.0M solution?
5.0moles
1.0Ln = M x V = x 0.1L =
Mar 2810:53 AM
Example #4How many grams of NaCl are contained in 450.0 mL of a 2.0M solution?
0.9 moles 58.5g
1 mole
2.0moles
1.0Ln = M x V = x 0.45L =
Mar 2810:52 AM
Example #5What volume (in mL) of 12.0M HCl is needed to have 5.00 moles of HCl?
5.0 molesV = =n
M 12.0moles
1.0L
Ch.16 sections 1 and 2 notes with notations
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April 12, 2018
Mar 262:59 PM
Making Dilutions
• The number of moles of solute does not change when a solution is diluted
• Adding water to an existing solution.
• Increasing the volume to lower Molarity
Apr 1112:48 PM
0.5L
8.0 M HCl
________
2.0 M HCl
How much water must be added to make 2.0 M HCl?
Mar 262:49 PM
M1 x V1 = M2 x V2• Volume can be in mL or L as long as they are the same on both sides.
• The number of moles are the same on both sides.
• Stock solution is M1 or the solution of greater concentration.
Dilution Formula
Mar 2810:51 AM
M1: 18.0 MV1:M2: 1.0 MV2: 4.50 L
Example #6
Concentrated H2SO4 is 18.0M, what volume is needed to make 4.50 L of 1.00M solution? How much water must be added to it?
The number of moles in each solution are the same!!!The difference between the 2 solutions is the amount of water you add.
Mar 262:48 PM
Mixing SolutionsCalculate the final concentration if 5.0L of 2.0M NaCl and 3.0L of 4.0M NaCl are mixed?
Step 1: Find total volume (Same units)
Step 2: Find total moles
Step 3: Calculate molarity
Mar 262:48 PM
Example #7
Calculate the final concentration if 4.00 L of 5.0M NaCl and 6.00 L of 2.0M NaCl are mixed?
Ch.16 sections 1 and 2 notes with notations
8
April 12, 2018
Mar 262:49 PM
Example #8
Calculate the final concentration if you added 5.0L of water to the mixture in example #7.
Mar 262:50 PM
Percent Solutions• Determining the percentage of solute in any given
solution.
• Not the same as molarity because every solute has a different molar mass
• Important when comparing different solutions!!
comparing 1.0M HCI vs. 1.0M H2SO4
Apr 157:47 AM
How do I compare 1.0-M HCl with 2.0-M HCl?
How do I compare 1.0-M HCl with 1.0-M H2SO4?
Mar 262:46 PM
g = mass
v = volume
% = % solution
Percent Solution mass of solutemL of solution
g
% V
(mL)
Mar 262:51 PM
Percent Solutions
% m/v of 2.0M NaCl
Molar Mass NaCl = 58.5
% m/v of 2.0M MgCl2
Molar Mass MgCl2 = 95
100g of NaCl is dissolved in 2.00L of
solution.
% m/v is always expressed in g/mL.
If you are given molarity, then you can always determine the mass per 1.0L.
Mar 263:04 PM
When there is a Liquid and a Solid.
• %(mass/vol.) = mass of solute (g) volume of solution (ml)
• Must be in g/mL!
Ch.16 sections 1 and 2 notes with notations
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April 12, 2018
Mar 263:04 PM
When both solvent and solute are Liquids!
% by vol. = vol. Solute X 100% vol. Solution Answer in: %(volume/volume)
Mar 263:04 PM
Example #9
What is the %(v/v) of ethanol when 75mL is diluted to a volume of 250 mL with water?
Mar 263:04 PM
Example #10
What is the percent (mass/volume) of NaCl in a 200.0 mL solution containing 14 grams of NaCl?
Mar 263:04 PM
Example #11
How many grams of glucose would you need to prepare 2.0 L of 2% (m/v) glucose solution?
Mar 263:04 PM
Example #12What is the %(v/v) of ethanol when 50 mL is diluted with 150 mL of water?
Mar 263:04 PM
16.3 Colligative Properties of Solutions
• Colligative properties depend on the number of particles dissolved in a given mass of solvent
1. Freezing Point
2. Vapor Pressure
3. Boiling Point
Ch.16 sections 1 and 2 notes with notations
10
April 12, 2018
Mar 263:04 PM
3 Colligative Properties
• Factors that change when Particles dissolve
• For the same substance, we compare Molarity!
• For different substances, we compare the number particles dissolved for 1 mole of a substance.
Mar 263:04 PM
Dissolved Particles
The more dissolved particles, the greater change in the colligative properties.
• Glucose: 1 molecule (1 particle)• NaCl: 2 ions (2 particles)• CaCl2: 3 ions (3 particles)
Mar 2810:29 AM
C6H12O6 NaCl CaCl2
1 mole6.02 x 1023 molecules
1 mole6.02 x 1023 form units
1 mole6.02 x 1023 form units
x 1 dissolved particle x 2 dissolved particles x 3 dissolved particles
Apr 168:16 AM
3.0M NaCl 1.8M AlCl3Which will have the most dissolved particles in 1L of solution?
3.0 moles x (6.02 x 1023) 1.8 moles x (6.02 x 1023)
x 2 particles (Na+ & Cl) x 4 particles (Al3+, Cl, Cl, Cl)
Mar 263:04 PM
3 Colligative Properties
1. vapor pressure lowering2. boiling point elevation3. freezing point depression
Mar 262:56 PM
30º CelsiusWater Salt Water
Vapor Pressure 4.24kPa
Boiling Point = 100ºC
Vapor pressure of the water must be 101.3kPa
to boil.
Vapor Pressure 3.69kPa
Boiling Point = 102 ºC
Vapor pressure of the water must be 101.3kPa to boil.
Ch.16 sections 1 and 2 notes with notations
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April 12, 2018
Mar 263:05 PM
Vapor Pressure
• Substances with high vapor pressure evaporate quickly.
• Substances with low vapor pressure evaporate slowly.
Mar 263:05 PM
Vapor Pressure
• Mercury 23°C = 0.000219kPa• Water 20°C = 2.3kPa• Water 90°C = 69.9kPa• Acetone 22.7°C = 26.7kPa
* Notice that hot water has a higher vapor pressure than cold water.
Mar 2810:27 AM
Freezing Point
• The more dissolved particles, the colder it needs to be for a solvent to freeze.• Antifreeze in cars.• Why is CaCl2 better to melt ice than NaCl?
Mar 262:54 PM
Boiling Point
• Vapor pressure of liquid equals vapor pressure of the air.
• The higher percentage of solute, the higher the boiling point.
• As water evaporates, the concentration of solute rises.
Mar 262:54 PM
Boiling Point
• Salt water has lower vapor pressure than fresh water.• Salt water will boil at 102 °C at a location with an atmospheric pressure of 1 atm.• Pasta will cook faster at 102 °C than 100 °C.
Mar 262:53 PM
High Altitude Directions
• At high altitudes, the atmospheric pressure is less than 101.3 kPa. (Denver = 84.0 kPa)
• In Denver, water boils at 94 °C so water reaches a boil faster but food cooks slower than at sea level.
Ch.16 sections 1 and 2 notes with notations
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April 12, 2018
Apr 1712:52 PM
36.2 g NaCl
100g H2Oat 25 °C
This is the solubility of salt in water at 25 °C.
• What happens to the solubility if temperature increases or decreases?
• How many grams of NaCl can be dissolved in 300 grams of water?
Apr 129:07 PM
Solubility CurvesA visual representation of how much of a substance can be dissolved in 100 grams of water, based on temperature
In general, the solubility of a substance will increase with temperature
Apr 19:32 PM
A gas has a solubility in water of 15.0 g/L at 400 kPa of pressure. Assuming constant temperature, what is the solubility of the gas at a pressure of 550 kPa?
Henry's Law
Apr 19:34 PM
What is the molarity of a 1.5 L solution containing 85.0 grams NaCl?
Apr 19:35 PM
Concentrated HCl is 16.0 M. What volume is needed to make 6.0 L of 4.0 M solution? How much water must be added?
M1:
V1:
M2:
V2:
Apr 19:38 PM
What is the final concentration if 6.5 L of 3.0 M NaCl and 4.5 L of 6.0 M NaCl are mixed, and an additional 3.0 L of water is added?