Solutions

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Solutions
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Types of Mixtures

• Heterogeneous mixtures-mixtures that do not blend
  smoothly-not uniform throughout-individual
  substances remain distinct.
• Two Types of Heterogeneous Mixtures are
• Suspensions
• Colloids

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Suspensions

• Suspensions-heterogeneous mixture that settles
  upon standing. Can be separated by filter paper.

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Colloids

• Colloids-heterogeneous mixtures that appear
  cloudy, cannot be separated by filtration, and
  demonstrate the Tyndall effect.

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Tyndall Effect
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Types of Mixtures (continued)

• Homogeneous mixtures-mixtures that do blend
  smoothly-uniform throughout-one set of
  properties.
• Homogeneous mixtures are called solutions.

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Solutions

• Solutions consist of
• Solute-part of the solution that gets dissolved
• Solvent-part of the solutions that does the
  dissolving
• Water is called the universal solvent.

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Types of Solutions
State of Solute State of Solvent Example
Gas Gas Air
Gas Liquid Soft drink
Liquid Liquid Antifreeze, vinegar
Liquid Gas Humidity
Liquid Solid Dental filling
Solid Liquid Ocean water
Solid Solid Bronze. Brass (alloys)

1. Enter answer text...

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Muddy water is an example of a

1. colloid
2. solution
3. suspension

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Fog is an example of a

1. colloid
2. solution
3. suspension

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Italian salad dressing is an example of a

1. colloid
2. solution
3. suspension

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Kool-aid is an example of a

1. colloid
2. solution
3. suspension

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Pure air is an example of a

1. colloid
2. solution
3. suspension

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Salt is dissolved in water. Salt is the

1. solute
2. solvent

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Sugar is dissolved in sweet tea. The tea is the

1. solute
2. solvent

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Oxygen gas dissolved in lake water is an example
of a

1. Liquid dissolved in a gas
2. Gas dissolved in a liquid
3. Gas dissolved in a solid
4. Solid dissolved in a gas

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Carbon dissolved in iron to make steel is an
example of a

1. Solid dissolved in a solid
2. Solid dissolved in a liquid
3. Solid dissolved in a gas
4. Liquid dissolved in a solid
5. Gas dissolved in a solid

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Properties of Solutions

• A substance that dissolves in a solvent is said
  to be soluble.
• Two liquids that are soluble in each other are
  said to be miscible.
• A substance that does not dissolve in a solvent
  is said to be insoluble.
• Two liquids that are not soluble in each other
  are said to be immiscible.

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Insoluble Solids
Immiscible Liquids
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Like Dissolves Like

• Polar substances dissolve other polar substances
  (or ionic compounds).

• Water is polar (due to asymmetrical arrangement
  of the molecule).

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Which of the following will dissolve in water?
This one because it is polar!
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Like Dissolves Like (continued)

• Nonpolar substances dissolve nonpolar substances.
• Polar substances cannot dissolve nonpolar
  substances.

Nonpolar iodine dissolves in nonpolar hexane
Nonpolar iodine does NOT dissolve in polar water
Nonpolar hexane and polar water do not mix.
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Corn oil does not dissolve in water. Corn oil is

1. Polar
2. nonpolar

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Will calcium chloride (CaCl2) dissolve in water?

1. Yes
2. No

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Which of the following is immiscible in water?

1. Food coloring
2. Vinegar
3. Gasoline
4. Lemon-aid

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Factors Affecting the Rate of Dissolving

• Agitation-(stirring)-stirring or shaking
  increases the rate at which solutes dissolve.
• Surface area-breaking up a solid increases the
  surface area and increases the rate at which
  solids dissolve
• Temperature-as temperature increases, the rate of
  dissolving of solid solutes increases.

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Solubility

• Solubility is defined as the amount of solute
  that will dissolve in a given amount of solvent
  at a particular temperature

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Solubility (cont.)

• Solutions that contain the maximum amount of
  dissolved solute at a given temperature are said
  to be saturated.
• Solutions that contain less than the maximum
  amount of solute are said to be unsaturated.
• Solutions that contain more than the expected
  maximum amount of solute are said to be
  supersaturated (can be accomplished only through
  heating and careful cooling of the solvent).

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Temperature and Solubility

• In warmer water, more solid will dissolve.
• This is because a high temperature means water
  molecules are moving faster which keeps more
  solid molecules suspended.
• Conversely a gas will be less soluble at a higher
  temperature.
• This is because when a gas molecules are moving
  faster they are able to escape from the liquid
  surface.

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Solubility Curves

• A solubility curve is a graph of the solubilities
  of various substances as a function of
  temperature.
• When graphing the data for solubility,
  temperature is the manipulated variable, and mass
  of solute dissolved is the responding variable.

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Interpreting Solubility Curves

• 1. What is the maximum amount of NaNO3 that will
  dissolve in 100 g of water at 10oC?
• 2. At what temperature will 70 g of NH4Cl
  dissolve in 100g of water?
• 3. Which substance has the greatest solubility
  at 0oC?
• 4. Which substance is the least soluble at
  100oC?
• 5. 15 g of KClO3 is dissolved in 100 g of water
  at 50oC. Is the solution saturated, unsaturated,
  or supersaturated?

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Concentration of Solutions

• Qualitative descriptions
• Concentrated solutions-large amount of solute and
  small amount of solvent.
• Dilute solutions-large amount of solvent and
  small amount of solute.
• Quantitative descriptions
• Solubility-grams of solute/ml of solution
• Molarity-moles of solute/L of solution
• Molality-moles of solute/kg of solvent
• Percent by Mass-mass of solute/mass of solution
  x100
• Percent by Volume volume of solute/volume of
  solution x 100

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Molarity

• A solution of NaCl has a molarity of 1 (1M).
  What does this mean?
• 1 mole of NaCl is dissolved in enough water to
  make 1 L.
• 1 mole 58 g NaCl
• A 1M solution of NaCl contains 58 g of NaCl
  dissolved in 1 liter of water.
• How much salt is dissolved in a 2M solution?
• 116 g
• How much salt is dissolved in a 6 M solution?
• 348 g
• Which is more concentrated?

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Molality

• A solution of NaCl contains 58 g of NaCl
  dissolved in 1 liter of water. The density of
  water is 1.00g/mL. What is the molality of the
  solution?
• 1 liter 1000 mL 1000 g 1 kg
• 58 g 1 mole
• Molality 1 mole/1 kg 1 m
• How much salt must be dissolved in 100 g of water
  in order to make a 2.0 molal (m) solution?
• 100 g .1 kg
• 2.0 x/.1
• X .2 moles x 58 g 11.6 g
• Will molarity and molality for the same solution
  always be equal? Explain.

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Colligative Properties

• Colligative properties are properties that depend
  on the number (not the type) of solute particles
  present in solution.
• Colligative properties include
• 1) freezing point
• 2) boiling point
• 3) vapor pressure

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Freezing Point Depression

• The freezing point of a solution is lower than
  the freezing point of the pure solvent.
• Example Saltwater freezes at a lower
  temperature than pure water (below zero degrees
  Celsius).
• The greater the number of ions in the solution,
  the lower the freezing point.
• Example
• NaCl consists of two ions Na and Cl-
• CaCl2 consists of three ions Ca2 , Cl- , and
  Cl-
• Which has the lower freezing point?
• CaCl2

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Boiling Point Elevation

• The boiling point of a solution is higher than
  the boiling point of the pure solvent.
• Example Saltwater boils at a higher temperature
  than pure water (at a temperature above 100
  degrees Celsius).
• The greater the number of ions in the solution,
  the higher the boiling point.
• Which boils at a higher temperature a solution
  of NaCl or a solution of CaCl2
• CaCl2

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Vapor Pressure Lowering

• Vapor pressure is the pressure exerted by the
  vapor particles on the surface of a liquid.
• The vapor pressure of a solution is lower than
  the vapor pressure of the pure solvent.
• Due to the presence of solute particles, fewer
  solvent particles are able to escape from the
  surface of the liquid resulting in a lower
  pressure.
• If the vapor pressure is lower, the boiling point
  will be higher.

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Which of the following is NOT a colligative
property?

• Boiling point
• 2. Density
• Freezing point
• Vapor pressure

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The freezing point of a solvent will ____ when a
solute is added.

1. go up
2. go down
3. remain the same

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The boiling point of a solvent will ____ when a
solute is added.

1. go up
2. go down
3. remain the same

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Which of the following solutes will result in a
solution having the highest boiling point?

1. NaCl
2. CaCl2
3. AlCl3
4. C12H22O11

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If cost was not an issue, which of the following
salts would be the most effective road deicer?

1. NaCl
2. CaCl2
3. AlCl3
4. All would be equally effective

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Which solution would have the lowest freezing
point?

1. 1 M AlCl3
2. 2 M NaCl
3. 3 M CaCl2
4. 4 M C6H12O6

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Problems Involving Colligative Properties

• The equation used to determine the Freezing Point
  Depression and Boiling Point Elevation is
• ?T i Kfm where
• ?T represents temperature change
• Kf is the freezing point depression constant
  (this value is specific to each solvent)
• m represents molality
• i represents the number of ions making up the
  solute.
• Note
• molality moles of solute/kg of solvent
• The same equation is used to determine the
  boiling point elevation however, Kb is
  substituted for Kf.

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Practice Problem

• Sodium chloride is often used to prevent icy
  roads and to freeze ice cream. What is the
  freezing point of a 0.029 m aqueous solution of
  sodium chloride?
• Molality 0.029
• Kf for water 1.86
• i 2
• ?T i Kfm
• ?T 2 (1.86) 0.029
• ?T .11
• 0 -.11 -.11oC

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Practice Problem 2

• A lab technician determines that the boiling
  point of an aqueous solution of a calcium
  chloride solution (CaCl2) is 101.12oC. What is
  the solutions molality?
• ?T 101.12 100 1.12
• Kb for water .512
• i 3 for CaCl2
• ?T i Kbm
• 1.12 3 (0.512) x
• X0.729 moles/kg of solvent

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Diluting Molar Solutions

• You can prepare a less concentrated solution from
  a more concentrated solution by diluting the
  solution (increase the solvent particles)
• The following equation can be used
• M1V1 M2V2 where
• M1 and V1 represent the molarity and volume of
  the concentrated solutions
• M2 and V2 represent the molarity and volume of
  the diluted solutions.

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Practice Problem

• How many milliliters of a 5.0 M H2SO4 solution
  would you need to prepare 100 mL of a 0.25 M
  H2SO4 solution?
• M1V1 M2V2
• M1 5.0 M
• V1 x
• M2 0.25 M
• V2100 mL
• M1V1 M2V2
• 5(x) 0.25 (100)
• X 5 mL