SolutionsWater

1
Solutions/Water

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• Mr. Chan
• Northwestern University

2
Day 9/15

• 45 Discuss HW/Quiz/Labs/Review
• 45 Quiz
• 60 Solutions
• 60 Lunch
• 90 Labs
• 75 Review/Intervention/Conferences

3
Solution Formation

• What is a solution?
• Common examples?
• How do you make one?
• What affects a solution?
• Affecting Rate vs. Affecting Amount

4
Determining Solubility

• Saturated solution
• Maximum amount of solute for a given amount of
  solvent at constant temperature
• Unsaturated solution
• Solution that contains less solute than a
  saturated solution
• Supersaturated solution
• Solution that contains more solute than it can
  hold at a given temperature
• Solubility
• Amount that dissolves in a given quantity of a
  solvent at a given temp
• Show Table of Solubilities
• Miscible vs. Immiscible
• 2 liquids miscible if dissolve in each other
• Immiscible insoluble in one another

5
Factors that Determine Rate of Dissolving

• How can you make something dissolve faster or
  slower?
• Nature of solvent and solute
• Stirring
• Temperature
• Surface Area

6
Affecting Solubility of Solutions and of Gas in
Liquid

• Temperature effects
• Increase temperature, increase solubility
• Gas/Liquid increase temp, decrease solubility
• Pressure effects
• Only for gases increase pressure, increase
  solubility
• Henrys law
• Solubility of gas proportional to pressure of gas
  above liquid
• Mentos/Diet Coke

7
Calculating Molarity of Solution

• Concentration
• Measure of amount of solute dissolved in solvent
• Dilute (small amount solute) vs. Concentrated
  (large amount of solute)
• Molarity
• Number of moles of solute dissolved per liter of
  solution
• Molarity moles/volume
• Moles M x V
• Examples
• A) 0.70 mol NaCl, volume 250 mL what is
  molarity?
• B) 36.0 grams glucose (180 g) in 2.0 L what is
  molarity?
• C) How many moles solute in 250 mL of 2.0M CaCl2?
  Grams?

8
Calculating Dilutions

• Moles of solute before dilution moles of solute
  after dilution
• Number of moles of solute does not change when
  solution is diluted
• M1 x V1 M2 x V2
• Examples
• A) need 250 mL of 0.20M NaCl, but you only have
  1.0M NaCl
• B) 5 mL of 1.0M KOH with 1L 0.5M KOH explain

9
Determining percent by volume and percent by mass

• Percent by volume ((v/v)) volume of
  solute/solution volume x 100
• Percent (mass/volume) mass of solute/solution
  volume x 100
• Think juice packets, fruit punch, etc.
• Examples
• A) percent by volume of ethanol when 75 mL of
  ethanol diluted to volume of 250 mL with water
• b) 2.7 grams of CuSO4 in 75 mL of solution. Calc
  percent (m/v) of solution.

10
Calculating Molality and Mole Fraction

• Molality number of moles of solute dissolved
  per kilogram of solvent
• Used in Colligative properties problems
• Examples
• What is molality of solution prepared by
  dissolving 10.0 grams of NaCl in 600.0 g of water
• Mole Fraction
• Ratio of moles of solute to total number of moles
  of solvent and solute
• Examples
• What is mole fraction of each component in a
  solution made by mixing 300.0 grams of ethanol
  and 500.0 grams of water?

11
Colligative Properties

• Depend only on number of particles dissolved in
  given mass of solvent
• Volatile vs. Nonvolatile solvents
• Solution with nonvolatile solute lower VP than
  pure solvent
• Proportional to number of particles the solute
  makes in solution (NaCl vs. glucose)
• Boiling Point Elevation
• Increase in BP due to solute
• Freezing Point Depression
• Decrease in FP due to solute

12
BP Elevation and FP Depression

• Change in temp Kb x molality
• Kb molal boiling point elevation constant
• Kb H2O 0.512 C/m
• Example
• What is the boiling point of a 2.00m NaCl
  solution?
• FP Depression
• Change in temp Kf x molality
• Kf molal freezing point depression constant
• Kf H2O 1.86 C/m
• Example
• What is the freezing point of a 2.00m NaCl
  solution?

13
Calculating Molar Mass

• Working backwards from FP/BP formulas
• Example
• 9.20 g compound in 35.0 g of water boils at 102
  degrees Celsius. What is the molar mass of the
  solute? Assume that the solute exists as
  molecules, not ions.

14
Colloids and Suspensions

• Suspensions mixtures where some of the
  particles will settle slowly upon standing
• Particles are much larger than those in a
  solution
• Colloids mixtures containing particles that are
  intermediate in size between suspensions and
  solutions
• Examples gelatin, smoke, milk, glue
• Tyndall effect
• Scattering of visible light in all directions

15
Hydrates

• Water in a crystal
• Compare hydrates to anhydrous solids
• Forces holding water molecules not very strong
• Effloresce
• To lose water of hydration
• Hygroscopic
• Compounds that remove moisture from the air
• Dessicants
• Drying agents, silica gel, packets in electronics
• Deliquescent
• Remove water from air to dissolve completely to
  form solutions

16
Lab Supersaturation (A/W 31)

• Objectives Experimental experience with
  supersaturation
• Techniques Start this experiment first.
• Air cool instead of ice water bath 20 minutes
• Work on other experiment while you wait
• Lab report, conferences about feedback, grades,
  etc.
• Questions No Going Further

17
Lab Factors Affecting Solution Formation (A/W
30)

• Objectives Experimental data on Factors that
  youre familiar with
• Questions No Design Experiment