1. Chapter 17 “Water and Aqueous Systems”
Milbank High School

2. Section 17.1 Liquid Water and it’s Properties
OBJECTIVES:
Describe the hydrogen bonding that occurs in water.

3. Section 17.1 Liquid Water and it’s Properties
OBJECTIVES:
Explain the high surface tension and low vapor pressure of water in terms of hydrogen bonding.

4. The Water Molecule
Each O-H bond is highly polar, because of the high electronegativity of the oxygen
bond angle = 105 o
due to the bent shape, the O-H bond polarities do not cancel. This means water as a whole is polar.
Fig. 17.2, p.475

5. The Water Molecule
Water’s bent shape and ability to hydrogen bond gives water many special properties!
Water: high surface tension, low vapor pressure, high specific heat, high heat of vaporization, and high boiling point

6. High Surface Tension liquid water acts like it has a skin
glass of water bulges over the top
Water forms round drops
spray water on greasy surface
All because water hydrogen bonds.
Fig. 17.4, p.476

7. Surface Tension d- One water molecule hydrogen bonds to another.
Also, hydrogen bonding occurs to other molecules all around. H O d+ d+ d- H O d+ d+

8. Surface Tension
A water molecule in the middle of solution is pulled in all directions.

9. Surface Tension Not true at the surface.
Only pulled down and to each side.
Holds the molecules together.
Causes surface tension.

10. Surface Tension
Water drops are round, because all molecules on the edge are pulled to the middle- not to the air!

11. Surface Tension Glass has polar molecules. Glass can hydrogen bond.
Attracts the water molecules.
Some of the pull is up a cylinder.

12. Meniscus
Water curves up along the side of glass.
Meniscus

13. Meniscus
In Plastic
In Glass

14. Surface tension All liquids have surface tension
water is higher than most others
How to decrease surface tension?
Use a surfactant - surface active agent

15. Low vapor pressure Fig. 17.6, p.477
Hydrogen bonding also explains water’s unusually low vapor pressure.

16. Specific Heat Capacity
Water has a high heat capacity (also called specific heat).
It absorbs 4.18 J/gºC, while iron absorbs only J/gºC.
Remember: SH = heat Mass x DT

17. Section 17.2 Water Vapor and Ice
OBJECTIVES:
Account for the high heat of vaporization and the high boiling point of water, in terms of hydrogen bonding.

18. Section 17.2 Water Vapor and Ice
OBJECTIVES:
Explain why ice floats in water.

19. Evaporation and Condensation
2,260 J/g is the heat of vaporization.
This much energy to boil 1 gram water
You get this much energy back when it condenses.
Steam burns, but heats things well.

20. Ice Solid metals sink in liquid metal. But, ice floats in water. Why?
Water becomes more dense as it cools until it reaches 4ºC.
As the molecules slow down, they arrange themselves into honeycomb shaped crystals.
(Fig. 17.9, p.481)

21. Liquid
Solid H O H O H O H O H O H O H O H O H O H O H O H O

22. Ice 10% greater volume than water. Water freezes from the top down.
The layer of ice on a pond acts as an insulator for water below
It takes a great deal of energy to turn solid water to liquid water.
Heat of fusion is: 334 J/g.

23. Section 17.3 Aqueous Solutions
OBJECTIVES:
Explain the significance of the statement “like dissolves like”.

24. Section 17.3 Aqueous Solutions
OBJECTIVES:
Distinguish among strong electrolytes, weak electrolytes, and nonelectrolytes, giving examples of each.

25. Solvents and Solutes
Solution - a homogenous mixture, that is mixed molecule by molecule.
Solvent - the dissolving medium
Solute -the dissolved particles
Aqueous solution- a solution with water as the solvent.
Particle size about 1 nm; cannot be separated by filtration!

26. Aqueous Solutions
Water dissolves ionic compounds and polar covalent molecules best.
The rule is: “like dissolves like”
Polar dissolves polar.
Nonpolar dissolves nonpolar.
Oil is nonpolar.
Oil and water don’t mix.
Salt is ionic- makes salt water.

27. How Ionic solids dissolve
Called solvation.
Water breaks the + and - charged pieces apart and surrounds them.
Fig , p. 483
In some ionic compounds, the attraction between ions is greater than the attraction exerted by water
Barium sulfate and calcium carbonate

28. How Ionic solids dissolve

29. Solids will dissolve if the attractive force of the water molecules is stronger than the attractive force of the crystal.
If not, the solids are insoluble.
Water doesn’t dissolve nonpolar molecules because the water molecules can’t hold onto them.
The water molecules hold onto each other, and separate from the nonpolar molecules.

30. Electrolytes and Nonelectrolytes
Electrolytes- compounds that conduct an electric current in aqueous solution, or in the molten state
all ionic compounds are electrolytes (they are also salts)

31. Electrolytes and Nonelectrolytes
Do not conduct? Nonelectrolytes.
Many molecular materials, because they do not have ions
Not all electrolytes conduct to the same degree
there are weak electrolytes, and strong electrolytes
depends on: degree of ionization

32. Electrolytes and Nonelectrolytes
Table 17.3, p.485 lists some common electrolytes and nonelectrolytes

33. Electrolyte Summary
Substances that conduct electricity when dissolved in water, or molten.
Must have charged particles that can move.
Ionic compounds break into charged ions:
NaCl ® Na1+ and Cl1-
These ions can conduct electricity.

34. Nonelectrolytes do not conduct electricity when dissolved in water or molten
Polar covalent molecules such as methanol (CH3OH) don’t fall apart into ions when they dissolve.
Weak electrolytes don’t fall completely apart into ions.
Strong electrolytes do ionize completely.

35. Water of Hydration (or Water of Crystallization)
Water molecules chemically bonded to solid salt molecules (not in solution)
These compounds have fixed amounts of water.
The water can be driven off by heating:
CuSO4.5H2O CuSO4 + 5H2O
Called copper(II)sulfate pentahydrate.
- heat
+ heat

36. Hydrates Table 17.4, p.486 list some familiar hydrates
Since heat can drive off the water, the forces holding it are weak
If a hydrate has a vapor pressure higher than that of water vapor in air, the hydrate will effloresce by losing the water of hydration

37. Hydrates
Some hydrates that have a low vapor pressure remove water from the air to form higher hydrates- called hygroscopic
used as drying agents, or dessicants
packaged with products to absorb moisture

38. Hydrates
Some compounds are so hygroscopic, they become wet when exposed to normally moist air- called deliquescent
remove sufficient water to dissolve completely and form solutions
Fig , p.487
Sample Problem 17-1, p.488 for percent composition

39. Section 17.4 Heterogeneous Aqueous Systems
OBJECTIVES:
Explain how colloids and suspensions differ from solutions.

40. Section 17.4 Heterogeneous Aqueous Systems
OBJECTIVES:
Describe the Tyndall effect.

41. Mixtures that are NOT Solutions
Suspensions: mixtures that slowly settle upon standing.
Colloids: heterogeneous mixtures with particles between size of suspensions and true solutions (1-100 nm)

42. Mixtures that are NOT Solutions
Many colloids are cloudy or milky in appearance when concentrated, but almost clear when dilute
do not settle out
cannot be filtered out
Colloids exhibit the Tyndall effect- the scattering of visible light in all directions.
suspensions also show Tyndall effect

43. Mixtures that are NOT Solutions
Flashes of light are seen when colloids are studied under a microscope- light is reflecting- called Brownian motion to describe the chaotic movement of the particles
Table 17.6, p.492 summarizes the properties of solutions, colloids, and suspensions

44. Mixtures that are NOT Solutions
Emulsions- colloids dispersions of liquids in liquids
an emulsifying agent is essential for maintaining stability
oil and water not soluble; but with soap or detergent, they will be.