Water

1
Water Aqueous solutions

• Unit 13

2

• Why Water?

3
Water

• Most common solvent
• A polar molecule
• O? -
• a hydrogen bond
• H?
• H?

4
Soluble and Insoluble Salts

• A soluble salt is an ionic compound that
  dissolves in water.
• An insoluble salt is an ionic compound that does
  not dissolve in water

5
Learning Check Use State Sheets

• Indicate if each salt is (1)soluble or (2)not
  soluble
• A. ______ Na2SO4
• B. ______ MgCO3
• C. ______ PbCl2
• D. ______ MgCl2

6
Solution S3

• Indicate if each salt is (1) soluble or
• (2) not soluble
• A. _1_ Na2SO4
• B. _2_ MgCO3
• C. _2_ PbCl2
• D. _1_ MgCl2

7
Solute and Solvent

• Solutions are homogeneous mixtures of two or
  more substances
• Solute
• The substance in the lesser amount
• Solvent
• The substance in the greater amount

8
Learning Check SF2

• Identify the solute and the solvent.
• A. brass 20 g zinc 50 g copper
• solute 1) zinc 2) copper
• solvent 1) zinc 2) copper
• B. 100 g H2O 5 g KCl
• solute 1) KCl 2) H2O
• solvent 1) KCl 2) H2O

9
Solution SF2

• A. brass 20 g zinc 50 g copper
• solute 1) zinc solvent 2)
  copper
• B. 100 g H2O 5 g KCl
• solute 1) KCl
• solvent 2) H2O

10
Nature of Solutes in Solutions

• Spread evenly throughout the solution
• Cannot be separated by filtration
• Can be separated by evaporation
• Not visible, solution appears transparent
• May give a color to the solution

11
Types of Solutions

• air O2 gas and N2 gas gas/gas
• soda CO2 gas in water gas/liquid
• seawater NaCl in water solid/liquid
• brass copper and zinc solid/solid

12
Formation of a Solution

H2O
Hydration
Na
Cl-
Na
Dissolved solute
Cl-
H2O
Na
Cl-
solute
13
Solutions

• Electrolytes
• Nonelectrolytes

14
Electrolytes

• Are substances that form positive() and negative
  (-) ions in water
• Conduct an electric current

15
Writing An Equation for a Solution

• When NaCl(s) dissolves in water, the reaction
  can be written as
• H2O
• NaCl(s) Na (aq) Cl- (aq)
• solid separation of ions in
  water

16
Electrolytes in the Body

• Carry messages send to and from the brain as
  electrical signals
• Maintain cellular function with the correct
  concentrations electrolytes

17
Strong Electrolytes are 100 ionized

• salts H2O 100ions
• NaCl(s) Na(aq) Cl-(aq) H2O
• CaBr2(s) Ca2(aq) 2Br- (aq)
• acids
• HCl(g) H2O H3O(aq) Cl-(aq)

18
Nonelectrolytes

• Dissolve as molecules only
• No ions are produced in water
• Do not conduct an electric current
• H2O
• C6H12O6 (s) ?? C6H12O6 (aq)
• glucose

19
Learning Check E1

• Select the products for each of the following in
  water
• H2O
• A. CaCl2 (s) 1) CaCl2 2) Ca2 Cl2-
  
• 3) Ca2 2Cl-
• H2O
• B. K3PO4 (s) 1) 3K PO43- 2) K3PO4
  
• 3) K3 P3- O4-

20
Learning Check E1 Solution

• Select the products for each of the following in
  water
• H2O
• A. CaCl2 (s) 3) Ca2 2Cl-
• H2O
• B. K3PO4 (s) 1) 3K PO43-

21
What affects solubility?

• Like Dissolves Like
• Temperature
• Pressure

22
Like dissolves like

• A ____________ solvent such as water is needed
  to dissolve polar solutes such as sugar and ionic
  solutes such as NaCl.
• A ___________solvent such as hexane (C6H14) is
  needed to dissolve nonpolar solutes such as oil
  or grease.

23
Liquids

• Miscible means the that to liquids can dissolve
  in each other.
• Immiscible means they cant

24
What affects solubility?

• For solids in liquids as the temperature goes up
  the solubility goes up.
• For gases in a liquid as the temperature goes up
  the solubility goes down.
• For gases in a liquid- as the pressure goes up
  the solubility goes up.

25
Learning Check SF4

• Which of the following solutes will dissolve in
  water? Why?
• 1) Na2SO4
• 2) gasoline
• 3) I2
• 4) HCl

26
Solution SF4

• Which of the following solutes will dissolve in
  water? Why?
• 1) Na2SO4 Yes, polar (ionic)
• 2) gasoline No, nonnpolar
• 3) I2 No, nonpolar
• 4) HCl Yes, Polar

27
Temperature and Solutions

• Higher temperature makes the molecules of the
  solvent move around faster and contact the solute
  harder and more often.
• Speeds up dissolving.
• Usually increases the amount that will dissolve.

28
Temperature and Solubility of Solids

• Temperature Solubility (g/100 g H2O)
• KCl(s) NaNO3(s)
• 0 27.6 74
• 20C 34.0 88
• 50C 42.6 114
• 100C 57.6 182
• The solubility of most solids (decreases or
  increases ) with an increase in the temperature.

29
Temperature and Solubility of Solids

• Temperature Solubility (g/100 g H2O)
• KCl(s) NaNO3(s)
• 0 27.6 74
• 20C 34.0 88
• 50C 42.6 114
• 100C 57.6 182
• The solubility of most solids increases with an
  increase in the temperature.

30
Temperature and Solubility of Gases

• Temperature Solubility (g/100 g H2O)
• CO2(g) O2(g)
• 0C 0.34 0.0070
• 20C 0.17 0.0043
• 50C 0.076 0.0026
• The solubility of gases (decreases or increases)
  with an increase in temperature.

31
Temperature and Solubility of Gases

• Temperature Solubility (g/100 g H2O)
• CO2(g) O2(g)
• 0C 0.34 0.0070
• 20C 0.17 0.0043
• 50C 0.076 0.0026
• The solubility of gases decreases with an
  increase in temperature.

32
Saturated and Unsaturated

• A saturated solution contains the maximum amount
  of solute that can dissolve.
• Undissolved solute remains.
• An unsaturated solution does not contain all the
  solute that could dissolve

33
How Much?

• Solubility- The maximum amount of substance that
  will dissolve at that temperature (usually g/L).
• Saturated solution- Contains the maximum amount
  of solid dissolved.
• Unsaturated solution- Can dissolve more solvent.
• Supersaturated- A solution that is temporarily
  holding more than it can, a seed crystal will
  make it come out

34
Making solutions

• What the solute and the solvent are
• Whether a substance will dissolve.
• How much will dissolve.
• A substance dissolves faster if-
• It is stirred or shaken.
• The particles are made smaller.
• The temperature is increased.
• Why?

35
Making solutions

• In order to dissolve the solvent molecules must
  come in contact with the solute.
• Stirring moves fresh solvent next to the solute.
• The solvent touches the surface of the solute.
• Smaller pieces increase the amount of surface of
  the solute.

36
Solubility

• The maximum amount of solute that can dissolve
  in a specific amount of solvent usually 100 g.
• g of solute
• 100 g water

37
Learning Check S1

• At 40?C, the solubility of KBr is 80 g/100 g
  H2O. Indicate if the following solutions are
• (1) saturated or (2) unsaturated
• A. ___60 g KBr in 100 g of water at 40?C
• B. ___200 g KBr in 200 g of water at 40?C
• C. ___25 KBr in 50 g of water at 40?C

38
Solution S1

• At 40?C, the solubility of KBr is 80 g/100 g
  H2O. Indicate if the following solutions are
• (1) saturated or (2) unsaturated
• A. 2 Less than 80 g/100 g H2O
• B. 1 Same as 100 g KBr in 100 g of water
• at 40?C, which is greater than its
  solubility
• C. 2 Same as 60 g KBr in 100 g of water,
• which is less than its solubility

39
Learning Check S2

• A. Why would a bottle of carbonated drink
  possibly burst (explode) when it is left out in
  the hot sun ?
• B. Why would fish die in water that gets too
  warm?

40
Solution S2

• A. Gas in the bottle builds up as the gas
  becomes less soluble in water at high
  temperatures, which may cause the bottle to
  explode.
• B. Because O2 gas is less soluble in warm water,
  the fish may not obtain the needed amount of O2
  for their survival.

41
What if they are immiscible?

• -Colloid
• -Suspension

42
Colloids

• Have medium size particles
• Cannot be filtered
• Separated with semipermeable membranes
• Scatter light (Tyndall effect)

43
Examples of Colloids

• Fog
• Whipped cream
• Milk
• Cheese
• Blood plasma
• Pearls

44
Suspensions

• Have very large particles
• Settle out
• Can be filtered
• Must stir to stay suspended

45
Examples of Suspensions

• Blood platelets
• Muddy water
• Calamine lotion

46
Measuring Solutions
47
Concentration

• A measure of the amount of solute dissolved in a
  certain amount of solvent.
• Concentrated solution has a large amount of
  solute.
• Dilute solution has a small amount of solute
• Sometimes g/l or g/mL of g/100 mL.
• But chemical reactions dont happen in grams

48
Molarity

• The number of moles of solute in 1 Liter of the
  solution.
• M moles/Liter
• What is the molarity of a solution with 2.0 moles
  of NaCl in 4.0 Liters of solution.
• What is the molarity of a solution with 3.0 moles
  dissolved in 250 mL of solution.

49
Making solutions

• Pour in a small amount of solvent
• Then add the solute and dissolve it
• Then fill to final volume.
• M x L moles
• How many moles of NaCl are needed to make 6.0 L
  of a 0.75 M NaCl solution?
• How many grams of CaCl2 are needed to make 625 mL
  of a 2.0 M solution?

50
Making solutions

• 10.3 g of NaCl are dissolved in a small amount of
  water then diluted to 250 mL. What is the
  concentration?
• How many grams of sugar are needed to make 125 mL
  of a 0.50 M C6H12O6 solution?

51
Learning Check SF3

• Identify the solute in each of the following
  solutions
• A. 2 g sugar (1) 100 mL water (2)
• B. 60.0 mL ethyl alcohol(1) and 30.0 mL
• of methyl alcohol (2)
• C. 55.0 mL water (1) and 1.50 g NaCl (2)
• D. Air 200 mL O2 (1) 800 mL N2 (2)

52
Solution SF3

• Identify the solute in each of the following
  solutions
• A. 2 g sugar (1)
• B. 30.0 mL of methyl alcohol (2)
• C. 50 g NaCl (2)
• D. 200 mL O2 (1)

53
Rate of Solution

• You are making a chicken broth using a bouillon
  cube. What are some things you can do to make it
  dissolve faster?
• Crush it
• Use hot water (increase temperature)
• Stir it

54
Learning Check SF6

• You need to dissolve some gelatin in water.
  Indicate the effect of each of the following on
  the rate at which the gelatin dissolves as (1)
  increase, (2) decrease,
• (3) no change
• A. ___Heating the water
• B. ___Using large pieces of gelatin
• C. ___Stirring the solution

55
Learning Check SF6

• You need to dissolve some gelatin in water.
  Indicate the effect of each of the following on
  the rate at which the gelatin dissolves as (1)
  increase, (2) decrease,
• (3) no change
• A. 1 Heating the water
• B. 2 Using large pieces of gelatin
• C. 2 Stirring the solution

56
Dilution

• Adding water to a solution

57
Dilutions

• The number of moles of solute doesnt change if
  you add more solvent.
• The moles before the moles after
• M1 x V1 M2 x V2
• M1 and V1 are the starting concentration and
  volume.
• M2 and V2 are the starting concentration and
  volume.
• Stock solutions are pre-made to known M

58
Practice

• 2.0 L of a 0.88 M solution are diluted to 3.8 L.
  What is the new molarity?
• You have 150 mL of 6.0 M HCl. What volume of 1.3
  M HCl can you make?
• Need 450 mL of 0.15 M NaOH. All you have
  available is a 2.0 M stock solution of NaOH. How
  do you make the required solution?

59
Colligative Properties

• Depend only on the number of dissolved particles
• Not an what kind of particle

60
Vapor Pressure

• The bonds between molecules keep molecules from
  escaping.
• In a solution, some of the solvent is busy
  keeping the solute dissolved.
• Lowers the vapor pressure.
• Electrolytes form ions when dissolved - more
  pieces.
• NaCl Na Cl- 2 pieces
• More pieces bigger effect.

61
Boiling Point Elevation

• The vapor pressure determines the boiling point.
• Lower vapor pressure - higher boiling point.
• Salt water boils above 100ºC
• The solvent determines how much.

62
Freezing Point Depression

• Solids form when molecules make an orderly
  pattern.
• The solute molecules break up the orderly
  pattern.
• Makes the freezing point lower.
• Salt water freezes below 0ºC
• How much depends on the solvent.

63
Molality

• a new unit for concentration
• m Moles of solute kilogram of solvent
• m Moles of solute 1000 g of solvent
• What is the molality of a solution with 9.3 mole
  of NaCl in 450 g of water?

64
Why molality?

• The size of the change in boiling point is
  determined by the molality.
• DTb Kb x m x n
• DTb is the change in the boiling point
• Kb is a constant determined by the solvent(pg
  387).
• m is the molality of the solution.
• n is the number of pieces it falls into when it
  dissolves.

65
What about Freezing?

• The size of the change in freezing point is
  determined by the molality.
• DTf -Kf x m x n
• DTf is the change in the boiling point
• Kf is a constant determined by the solvent
• m is the molality of the solution.
• n is the number of pieces it falls into when it
  dissolves.

66
Problems

• What is the boiling point of a solution made by
  dissolving 1.20 moles of NaCl in 750 g of water?
• What is the freezing point?
• What is the boiling point of a solution made by
  dissolving 1.20 moles of CaCl2 in 750 g of water?
• What is the freezing point?

67
Piece of Cake!!!