Solutions

1
Chapter 15

• Solutions

2
Characteristics of Solutions

• They are homogeneous mixtures
• Solute substance that dissolves
• Solvent dissolving medium (thing that does the
  dissolving)
• Example salt water is a solution, salt is the
  solute, water is the solvent
• May be a gas, liquid, or solid, depending on the
  solvents phase
• Aqueous solutions are dissolved in water as a
  solvent

3
More Characteristics

• Soluble (solid-liquid) when a substance is able
  to dissolve in a solvent
• Sugar is soluble in water
• Insoluble (solid-liquid) when a substance is
  not able to dissolve in a solvent
• Sand is insoluble in water
• Miscible (liquid-liquid) when two liquids are
  soluble in each other
• Ethylene glycol is miscible in water
• Immiscible (liquid-liquid) when two liquids are
  not soluble in each other
• Oil is immiscible with water

4
Solvation

• Solvation process of surrounding solute
  particles with solvent particles to form a
  solution
• Hydration solvation where water is the solvent

5
Aqueous Solutions of Ionic Compounds

• See figure 15-10 p. 512 if necessary

6
Aqueous solutions of Molecular Compounds

• As long as the molecule is polar, then it is most
  likely soluble in water.
• If the molecule is nonpolar, it is definitely not
  soluble in water.
• See figure 15-11 p. 513 for diagram

7
Factors Affecting Rate of Solvation

• Goal is to increase the number of collisions
  between solute and solvent particles
• Agitation
• Shaking or swirling koolaid packet in water
• Increasing the surface area of the solute
• Grinding sugar into crystals rather than
  remaining in a cube
• Increasing temperature of the solvent
• Sugar dissolves faster in hot tea vs iced tea

8
Why do these factors affect the rate of solvation?

• Increase Surface Area
• Agitation
• Increased Temperature

9
Types of solutions

• Saturated Solution solution that contains the
  maximum amount of dissolved solute for a given
  amount of solvent at a specific temperature and
  pressure. (No more solute can be dissolved)
• Unsaturated Solution solution that contains
  less dissolved solute for a given temperature and
  pressure than a saturated solution. (Lots of
  solute can still be dissolved in the solute)
• Supersaturated Solution solution that contains
  more dissolved solute than a saturated solution
  at the same temperature. (Placing a seed crystal
  will cause the dissolved solute particles to
  crystallize)

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Solubility

• Solubility amount of solute that will dissolve
  in a given amount of solvent under given
  conditions
• (max. amount of solid that can dissolve in the
  liquid for specific pressures and temperatures)
• What kind of solution are we making?
• Usually expressed in g solute/100 g solvent

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Factors Affecting Solubility Nature of Solute
and Solvent

• When two substance are similar, they can dissolve
  in each other.
• Polar solutes dissolve in polar solvents.
• Nonpolar solutes dissolve in nonpolar solvents.
• Example?
• Summarized as like dissolves like

12
Factors Affecting Solubility Temperature on
Gases

• Temperature generally, most substances are more
  soluble at higher temperaturesthere are always
  exceptions
• Do you think gases are
  more or less soluble at
  high
  temperatures?
• Why?

13
Factors Affecting Solubility Temp on Solids

• Temperature generally, most substances are more
  soluble at higher temperatures, but there are
  always exceptions
• Using the solubility curve on the next slide,
  determine
• Which substances are more soluble as we
  increase temperature?
  
• Which substances are more soluble as we decrease
  temperature?

14
Solubility Curve
15
Using a solubility curve

• We can use a solubility curve to determine
• Whether a solution is unsaturated, saturated, or
  supersaturated.
• Which temperature is necessary to make a
  saturated solution.

16
Factors Affecting Solubility Pressure on Gases

• Pressure gases are more soluble in liquids if
  the external pressure exerted on them is
  increased
• Carbonation carbon dioxide is dissolved into
  the liquid at a higher pressure than 1 atm

17
Solution Concentration

• Concentration measure of how much solute is
  dissolved in a specific amount of solvent or
  solution
• Qualitatively we say something is either
  concentrated or dilute

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MOLARITY (extremely important)

• Molarity (M) number of moles of solute
  dissolved per liter of solution
• Molarity moles of solute liters of
  solution
• Example Calculate the molarity of 1.60 L of
  a solution containing 1.55 g of dissolved KBr.

19
Preparing Molar Solutions

• This is a solid into a liquid calculation
• Example How many grams of CaCl2 should be
  dissolved in 500.0 mL of water to make a 0.20 M
  solution of CaCl2?

20
Preparing Molar Solutions part deux

• This is a liquid into a liquid calculation
• DILUTION
• The number of moles of solute does not changethe
  volume of the solvent changes!
• M1V1M2V2 where 1stock solution and
  2diluted solution
• Example What volume of a 3.00 M KI stock
  solution would you use to make 0.300 L of a 1.25
  M KI solution?

21
Colligative Properties

• Colligative properties physical properties of
  solutions that are affected by the number of
  particles, but not the identity of dissolved
  solute particles
• Colligative means depending on the collection

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How are colligative properties affected?
Colligative Property Increase the number of particles and it
Vapor Pressure decreases
Boiling Point increases
Freezing Point Decreases
23
Boiling Point Elevation

• Recall boiling point is the temp at which vapor
  pressure external pressure
• Addition of solute causes vapor pressure to
  decrease, so we need a higher temp to make the
  vapor pressure increase high enough to cause
  boiling.
• Example Placing NaCl in a pot of boiling
  spaghetti to prevent boiling over.

24
Freezing point Depression

• Freezing point is the temp at which vapor
  pressures of both the solid and the liquid are
  the same.
• Vapor pressure reduces, so the temp at which the
  solid and the solution have the same vapor
  pressure is reduced.
• Example Rock salt is used to make ice cream.