1. Water and Aqueous Systems
Ch. 17

2. Liquid Water and its Properties
17-1

3. The Water Molecule, in review…
The water molecule, H – O – H, is made up of covalent bonds that are highly polar.
It has a bent shape with 105° bond angles.
Oxygen has a slightly negative charge (more electronegative), while Hydrogen has a slightly positive charge.
Water molecules attracted to each other through hydrogen bonds.

4. DRAW!

5. Many unique and important properties of water are due to it’s hydrogen bonds! Including its…
High surface tension
Low vapor pressure
High specific heat capacity
High heat of vaporization
High boiling point
Ice is less dense than water
17-1
17-2

6. Surface Properties
1. Surface tension = inward force, or pull, that tends to minimize the surface area of a liquid.
Due to the hydrogen bonding (attraction) between water molecules.
Water has HIGH surface tension, holds drops in a spherical shape.
Surfactant = wetting agent, soap or detergent, that decreases surface tension (interferes with H-bonding)
2. LOW vapor pressure; hydrogen bonds keep water in liquid form from escaping into gaseous form.

8. Specific Heat Capacity
3. Specific Heat Capacity (C) = it takes 4.18 J (1 cal) of heat energy to raise the temperature of 1g of water 1°C.
Due to hydrogen bonding, water has a HIGH specific heat capacity
Cwater = 4.18 J/(g°C)
C = Q = heat (J or cal)
m x ΔT mass (g) x (°C)

9. Water Vapor and Ice
17-2

10. Evaporation + Condensation
Heat of Vaporization = amount of E needed to convert 1g of a substance from liquid to gas at the boiling point.
Water has a HIGH heat of vaporization due to H-bonding
Heat of Vaporization = Heat of Condensation
Hvap of water = 2.26 kJ/g or 2260 J/g
Hfus of water = 334 J/g
Phase change use: H = m x Hvap/fus
Temp. change use: H = m x ΔT x C

11. Remember… When to use which H equation: Temp. Change Phase Change
H = m x ΔT x Csteam
Exothermic
H = m x Hvap
100°C
Temperature (°C)
H = m x ΔT x Cwater
H = m x Hfus
0°C
Endothermic
H = m x ΔT x Cice
Heat Energy

12. Boiling Point
Usually molecular compounds with a low molar mass have a low boiling point.
5. Water has a HIGH boiling point due to hydrogen bonding!

13. Ice Typically the density of a solid is greater than it’s liquid.
6. Ice is less dense than water!
Hydrogen bonding holds water molecules in a rigid framework, crystallize (spaced far apart – larger volume, less dense)
As it melts the framework collapses (closer together, more dense).

15. Aqueous Solutions
17-3

16. Solvents + Solutes
Aqueous solution = water containing dissolved substance.
Solute = dissolved particle.
Solvent = dissolving medium; always water in an aqueous solution.
Ionic compounds + polar covalent molecules dissolve easily.
Nonpolar covalent molecules do not dissolve easily.

17. The Solution Process
Solvation = the process that occurs when a solute dissolves.
Ionic + Polar = negative and positive ions or poles are attracted to different regions of water molecule and are pulled apart.
“Like dissolves like” –
Ionic + polar substances can dissolve together.
Ex: salt water (NaCl is ionic; water is polar).
Nonpolar and nonpolar substances can dissolve together.
Ex: gasoline + oil dissolve together, both are nonpolar!

18. Why don’t oil +
water mix??

19. Electrolytes + Nonelectrolytes
Electrolytes = compounds that conduct electric current in aqueous solutions or in a molten state.
ALL ionic compounds and most polar molecules are electrolytes.
Nonelectrolytes = compounds that do not conduct electric current in either aqueous or molten state.
Many molecular (nonpolar) compounds are nonelectrolytes since they are not made up of ions

20. Weak electrolyte = only a fraction of solute exists as ions in solution (not dissolve completely, usually polar).
Ex: HgCl2, NH3, sugar
Strong electrolyte = almost all of solute exists as separate ions in solution (dissolves completely, usually ionic).
Ex: NaCl, HCl, KCl

22. Water of Hydration Water of Hydration = the water in a crystal.
Hydrate = a compound that contains
water of hydration.
Ex: CuSO4(aq)  CuSO4•5H2O(s)
blue liquid blue crystals (hydrate)
CuSO4•5H2O (s)  CuSO4(s) + 5H2O(g)
white anhydrous powder
evaporates
heated

23. CuSO4(s) – Anhydrous Copper
CuSO4•5H2O(s)
Copper (II) Suflate
Pentahydrate
CuSO4(s) – Anhydrous Copper
(II) Sulfate

24. Energy Source + Global Warming Pollutant
Methane hydrate… a solid form of water that contains a large amount of methane within its crystal structure [that] occur both in deep sedimentary structures, and as outcrops on the ocean floor.
“Fire Ice”
Energy Source + Global Warming Pollutant

25. Hydrate Formula Writing a hydrate formula: Name of compound,
Prefix (# of water) “-Hydrate”
Ex: MgSO4•7H2O
Magnesium sulfate heptahydrate
Ex: Ba(OH)2•8H2O
Barium hydroxide octahydrate
Ex: Sodium sulfate decahydrate
Na2SO4•10H2O
Ex: Calcium chloride dihydrate
CaCl2•2H2O
Writing an anhydrous formula:
Ex: MgSO4•7H2O(s)
MgSO4(s) + 7H2O(g)

26. Hydrates
Hydrates lose or gain water easily because forces keeping them together are weak.
A hydrate which evaporates easily will effloresce – lose water of hydration
Hydrate  Anhydrous
Hydrates that remove water from air easily (gain water) are called hygroscopic
Anhydrous  Hydrate
Used as drying agents –
dessicants.

27. Deliquescent compounds remove sufficient water from the air to dissolve completely and form solutions!

28. % Mass % Mass = grams part x 100% grams whole
Ex: Calculate the % mass of water in CuSO4•5H2O.
% mass of water = H2O x 100%
CuSO4•5H2O
= 90g x 100% = 36.0% water
249.6g

29. Heterogeneous Aqueous Systems
17-4
NO CLASS IS DOING THIS
SECTION!!

30. Suspensions
This chapter has focused on homogeneous solutions, now we will look at heterogeneous mixtures.
Suspensions = mixture from which particles settle out upon standing.
Particles are fairly large
Can be separated through filtration.

31. Colloids
Colloids = heterogeneous mixture containing particles of intermediate size.
Can be in solid, liquid, or gas phase
Ex: glue, gelatin, paint, aerosol sprays, smoke
Do not settle out with time and cannot be separated by filtering.
Exhibit Tyndall effect, scattering of visible light in all directions.
Brownian motion = chaotic movement of colloidal particles; caused by collisions of particles with water molecules – prevents particles from settling!

33. Tyndall Effect

34. Brownian Motion