1. Chapter 17 Water & Aqueous Systems
17.1 Liquid Water and its Properties
Why do we care about water? 3/4 of earths surface, 60% of our body weight
Unique properties make life possible

2. Water Molecule Polar Bonds – difference in electronegativity is 1.4
Polar Molecule – has a bent shape due to lone pair electrons on the central element, oxygen
O: 3.5 H:2.1
How polar is it?
Address angle

3. Water Molecule
Molecules are attracted to each other by hydrogen bonds ∂-
Polar Covalent bond O ∂+ H H
Remember ∂ means partial or slightly.
Intermolecular vs. Intramolecular ∂- O H H
Hydrogen bond ∂+

4. Surface Tension
The inward force, or pull, that tends to minimize the surface area of a liquid
Tends to hold a drop of liquid in a spherical shape
A sphere has the smallest surface area for a given volume
Skin like properties (waterstrider)
Surface molecules attracted to each other through H-bonding and can’t h-bond to air
H-bonding is the reason for water beading up
Cohesion-attraction of water to water (surface tension)
Adhesion -attraction of water to non water (water sticking to a surface)

5. Surface Tension Water’s surface tension is stronger than most liquids
reduces vapor pressure
Define vapor pressure, h-bonds hold liquid together, h-bonds must break to increase vapor pressure

6. Surface Tension
Surfactant – substance that interferes with the hydrogen bonds between water molecules. Surface tension breaks down and the water spreads out.
Surface active agent
Why we use soap
Decreases surface tension

7. Thermochemistry
Specific heat capacity – the amount of energy required to raise the temperature of 1.0 g of water by 1C.
q = m  C  T
C = 1.00 cal/g°C or 4.18 J/g°C
m = mass in grams
∆T = change in temperature in °C
q = heat in joules or calories
Thermochem properties of water are incredibly important

8. Impact of Thermochemical Properties
Water allows for more temperate climates.
Water cools more slowly at night and heats more slowly during the day reducing temp variations

9. Chapter 17 Water & Aqueous Systems
17.2 Water Vapor & Ice

10. Water Vapor
Evaporation – the change of state from liquid to gas at the surface of a liquid that is not boiling
Ever left a glass out over night?
Endothermic- ex: sweat, Rubbing alcohol (colder because evap is faster, less h-bonds)

11. Water Vapor Condensation – the change of state from a gas to a liquid
Water has a high heat of vaporization
(2260 J/g)
2260 J of energy is needed to change 1.0 g of water from liquid to gas
2260 J of energy is given off when 1.0 g of water is changed from a gas to a liquid
Breathing on a cold day
A cold glass sweating
Exothermic
Where does the water come from that condenses on the cup? In the breath?

12. Water Vapor
Why would a burn from steam at 100C be worse than a burn from water at 100C?
Liquid water
2260 J/g more heat in steam than liquid
100°C
steam ∆q

13. Water Vapor
Water’s high boiling and melting points are caused by hydrogen bonding
When compared to ammonia (NH3) the H – bonds in water are stronger
It takes more energy to disrupt these bonds, giving water a higher boiling and melting point
H2o: 2 lone pairs 2 hydrogens more polar bonds (1.4)
Nh3: 1 lone pair 3 hydrogens (.9)

14. Ice Freezing – the change of state from a liquid to a solid
Water has a high heat of fusion (334 J/g)
334 J of energy is needed to change 1.0 g of water from a solid to a liquid

15. Ice
Density – the ratio of the mass of an object to its volume M
D = V

16. Ice
What happens when water freezes?

17. Ice What are some benefits of ice floating?
Insulates fish in winter, ground & air cold, ice keeps water warm, like eskimos

18. Review Problems
Calculate the heat released when a cup of tea cools from 61C to 25C. The mass of the tea is 225g. (Assume the specific heat of the tea is equivalent to that of water)
C = 4.18 J/g°C
m = 225 g
∆T = 61°C - 25°C = 36°C
q = ?
q = m  C  T
= 225g  4.18 J/g°C  36° C
= J
Variables, formular, plug in, solve, units, sig digs
100°C
0°C
Heat change

19. Review problems
Calculate the amount of heat needed to boil (vaporize) a kettle filled with water (250 g).
m = 250g
Hvap= 2260 J/g
q = ?
q = m • Hvap
q = 250g • 2260 J/g
q = J
Assume water is already at 100°C

20. Review Problems
How much heat energy is needed to melt 30.0 g of ice at 0C to water at 80C?
C = 4.18 J/g°C
Hfus= 334 J/g
m = 30 g
∆T = 80°C - 0°C = 80°C
q = ?
q1 = m • Hfus
q2 = m  C  T
= 30g * 334 J/g
= J
= 30g  4.18 J/g°C  80° C
= J + 2.
T when there is temp change, no temp change during phase change
20100 J
100°C 1
0°C 2
Heat change

21. Review Which atom in the water molecule is most electronegative?
a. Hydrogen
b. Oxygen
c. neither

22. Review How are water molecules held together? a. magic
b. dispersion forces
c. covalent bonds
d. hydrogen bonds

23. Review
Water has a ________________ vapor pressure due to _________________.
a. low; magic
b. high; no reason
c. low; hydrogen bonds
d. high; hydrogen bonds

24. Review
Water has a ________________ heat capacity and a __________________ heat of vaporization.
a. high; low
b. high; high
c. low; high
d. low; low

25. Review
Due to the high heat capacity and vaporization energy of H2O, coastal areas have ___________________ temperatures.
a. moderate
b. extreme
c. low
d. high

26. Review Which of the following are characteristics of surface tension?
a. reduces vapor pressure
b. holds liquids in spherical shapes
c. is caused by hydrogen bonding
d. is very strong in water
e. all of the above

27. Review
A surfactant is a substance that interferes with ________________ and decreases the _________________.
a. free time; productivity
b. hydrogen bonding; surface tension
c. intramolecular forces; vapor pressure

28. Chapter 17 Water & Aqueous Systems
17.3 Aqueous Solutions

29. Solutions
Aqueous solution – a water solution containing dissolved substances
Solvent – the dissolving medium
Solute – particles dissolved in the solution
Would the salt or the water be the solute in a salt-water solution?
Salt

30. Solutions
Solvation – the process that occurs when a solute dissolves in a solvent
EXAMPLE:
Liquid water is constantly in motion, particle collisions break up solute into ions

31. Solutions “Like Dissolves Like”
Polar substances dissolve in polar solvents.
H2O: polar and ionic
Nonpolar substances dissolve in nonpolar solvents
Gasoline: oil

32. Solutions
Electrolytes – compounds that conduct an electric current in aqueous solutions or in a molten state
All ionic compounds
Some very polar molecules dissolved in H2O
Electrolytes in gatorade: citric acid, salt, sodium citrate, monopotassium phosphate, sucrose acetate isobutyrate

33. Solutions
Nonelectrolytes – compounds that do not conduct an electric current in either aqueous solutions or the molten state
Molecular compounds
Organic compounds (carbon containing compounds)
Nonpolar compounds
Cane sugar, rubbing alcohol, not composed of ions H C H H H

34. Solutions Strong electrolytes: Weak electrolytes:
Nearly all the ions dissolve
in aqueous solution
NaOH, HCl and NaCl
Weak electrolytes:
Very small fraction of ions dissolve in aqueous solution
Distilled H2O, ammonia and
acetic acid

35. Solutions How electrolytes form: NH3 + H2O → HCl + H2O → NH4+ + OH-
H3O Cl-

36. Hydration Water of hydration – water in a crystal
When copper (II) sulfate is dissolved in water and then the water allowed to evaporate, copper (II) sulfate pentahydrate is formed
CuSO4 + 5H2O ↔ CuSO45H2O
Hydrate - compound that contains water of hydration
Dot used to connect formula of compound and # of water molecules per unit
CoCl2 is blue
CoCl2•6H2O is red
Give them words have them predict products/reactants

37. Hydration
When cobalt (II) chloride is dissolved in water and then the water allowed to evaporate, cobalt (II) chloride hexahydrate is formed
CoCl H2O
↔ CoCl2 6H2O

38. Naming Hydrates To name a hydrate, use the following:
They are named by giving the name of the salt followed by a prefix denoting the number of water molecules associated with a formula unit of the salt.
Ex: CuSO4 • 5H2O
copper (II) sulfate
penta
hydrate

39. Hydration Calculate the percent water in CuSO4•5H2O. Cu 1 S 1
Total mass of hydrate: g
Mass H2O:
H 2
O 1
Total mass of H2O: g X 5 = 90.0g
x 63.5 = 63.5
x 32.1 = 32.1
x 16.0 =
x = 10.0 +
x 1.0 = 2.0
x 16.0 = 16.0 +

40. Hydration
Mass H2O
Mass Hydrate
X 100 = % H2O
90g
X 100
= 36.1%
249.6g

41. Compound(high pressure)
H2O(low pressure)
Hydration
Compound(high pressure)
Efflorescence – process in which hydrated compounds lose water to its surroundings.
Occurs when a substance has a vapor pressure higher than that of water
Some hydrated compounds can effloresce and will form anhydrous compounds
In this process the compound loses water

42. Compound(low pressure)
H2O(high pressure)
Hydration
Compound(low pressure)
Deliquescence – process in which anhydrous or somewhat hydrated compounds gain water from the surroundings.
Occurs when the solution formed has a vapor pressure lower than that of the water in the air
Some anhydrous or somewhat hydrated compounds will deliquesce and form hydrated, or more hydrated, compounds
In this process water is gained

43. Hydration
Desiccants – hygroscopic (water absorbing) substances that are used as drying agents.
Small silica gel packets used in electronic merchandise shipping
Sodium hydroxide is a dessicant and becomes a solution quickly (dissolves itself) when exposed to water in the air

44. Chapter 17 Water & Aqueous Systems
17.4 Heterogeneous Aqueous Systems

45. Suspensions
Suspensions – mixtures from which particles settle out upon standing.
Suspensions have particle sizes larger than solutions
Generally the sizes are larger than 100 nm
The particle size in a solution is about 1 nm
Muddy water is a good example

46. Colloids
Colloids – heterogeneous mixtures containing particles that are intermediate in size between solutions and suspensions
Generally the sizes are
between 1 nm and 100 nm
Examples include glues,
gelatin deserts, paint, aerosols
and smoke
Define heterogeneous- 2 substances can be separated
Whipped cream, marshmellows, milk
Appear cloudy maybe even clear if very dilute, will not settle out
Cannot be filtered with paper filters (like coffee filters)

47. Colloids
Tyndall effect - the scattering of light in all directions. Suspensions also exhibit this effect, but solutions do not.
Fog, ever turned on headlights in fog seen everything light up? That is the tyndall effect
H2O constant motion hitting colloid and causing them to move as well
Called brownian because it was discovered by Robert Brown-Scottish Botanist

48. Colloids
Brownian motion – the chaotic movement of colloidal particles. Under a microscope the particles seem to be moving about erratically.
Example

49. Emulsions Emulsion – a colloidal dispersion of liquids in liquids.
Emulsifying agents are used to keep the emulsion stable.
Soap and detergents are good emulsifying agents
Mayonnaise is an emulsion. Know the main ingredients?
How emulsifying agents work- one polar end 1 not polar end
Ex: oil is attracted to non polar end water attracted to polar end
Vinegar, oil, egg yolk

50. Review What is the purpose of a surfactant?
To decrease surface tension by disrupting h-bonds

51. Review What type of process is the freezing of water?
Exothermic, heat is released

52. Review
What type of molecule is water?
Nonpolar/polar/ionic

53. Review
What types of compounds dissolve in water?
Polar/ionic

54. Review Which of these compounds would dissolve in water?
CH4 NH3 NaNO3 N2

55. Review
What is solvation?
Process that occurs when a solute dissolves

56. Review
In the hydrate CuSO45H2O how many water molecules would be present in 3 formula units? 15

57. Review
In the hydrate CuSO45H2O how many hydrogen atoms would be present in 3 formula units? 30