1. Ch. 15: Water and Aqueous Systems
15.1 Water and Its Properties surface tension, vapor pressure, hydrogen bonding
15.2 Homogenous Aqueous Systems aqueous solution, solvent, solvation, electrolyte, hydrate
15.3 Heterogenous Aqueous Systems
suspension, colloid, Tyndall effect, (Brownian motion, coagulation, emulsion)
Water covers about three quarters of Earth’s surface. All life forms that are known to exist are made mostly of water. You will learn about the properties of water and what makes this unique substance essential to life on Earth.

2. 15.1 Water and Its Properties
Many unique and important properties of water—including its high surface tension and low vapor pressure—result from hydrogen bonding.
Water in the Liquid State
How can you account for the high surface tension and low vapor pressure of water?
You could not live without water, nor could all the plants and animals on Earth.

3. Water in the Liquid State
15.1
Water in the Liquid State
A water molecule is polar.
In a water molecule, the bond polarities are equal, but the two dipoles do not cancel each other because a water molecule is bent. The molecule as a whole is polar. Applying Concepts Which element in water has the higher electronegativity?

4. Water in the Liquid State
15.1
Water in the Liquid State
Polar molecules are attracted to one another by dipole interactions. The negative end of one molecule attracts the positive end of another molecule.
The intermolecular attraction among water molecules results in the formation of hydrogen bonds.
The polarity of the water molecule results in hydrogen bonding. a) Partial negative charges are on each oxygen atom; partial positive charges are on the hydrogen atom. b) Because of polarity, hydrogen bonds form. Inferring To form a hydrogen bond, what must be true about the hydrogen and the element to which it is hydrogen bonded?

5. Water in the Liquid State
15.1
Water in the Liquid State
Surface Tension
The inward force, or pull, that tends to minimize the surface area of a liquid is called surface tension.
All liquids have a surface tension, but water’s surface tension is higher than most.
Surface tension makes it possible for this water strider to walk on water.

6. Water in the Liquid State
15.1
Water in the Liquid State
A surfactant is any substance that interferes with the hydrogen bonding between water molecules and thereby reduces surface tension. (examples are soaps and detergents)
Vapor Pressure
Hydrogen bonding between water molecules also explains water’s unusually low vapor pressure. Because hydrogen bonds hold water molecules to one another, the tendency of these molecules to escape is low, and evaporation is slow.

7. Water in the Solid State
15.1
Water in the Solid State
Water in the Solid State
As water begins to cool, it behaves initially like a typical liquid. It contracts slightly and its density gradually increases. When the temperature of the water falls below 4˚C, the density of water starts to decrease.

8. Water in the Solid State
15.1
Water in the Solid State
Hydrogen bonds hold the water molecules in place in the solid phase.
Extensive hydrogen bonding in ice holds the water molecules farther apart in a more ordered arrangement than in liquid water. The hexagonal symmetry of a snowflake reflects the structure of the ice crystal.
The structure of ice is a regular open framework of water molecules arranged like a honeycomb.
When ice melts, the framework collapses, and the water molecules pack closer together, making liquid water more dense than ice.

9. 15.1 Section Quiz.
1. Many of the unusual properties of water are the result of
a) hydrogen bonding.
b) nonpolar molecules.
c) low molar mass.
d) dispersion forces.

10. 15.1 Section Quiz.
2. A surfactant causes water to spread out over a surface. This spreading occurs because the surfactant
a) attaches to the surface.
b) interferes with hydrogen bonding.
c) lowers the vapor pressure.
d) lowers the density of water.

11. 15.1 Section Quiz.
3. Ice is less dense than liquid water because in ice the water molecules
a) expand because of weakened covalent bonds.
b) have a regular open honeycomb framework.
c) expand because of weakened hydrogen bonds.
d) have a more disorderly arrangement with lower density.

12. 15.2 Homogeneous Aqueous Systems
An ordinary dill pickle from the deli can be a source of light! Iron or copper electrodes are inserted into the ends of the pickle and connected to a source of alternating electric current. You will learn what kind of solution conducts electricity.

13. 15.2
Solvents and Solutes
An aqueous solution is water that contains dissolved substances.
In a solution, the dissolving medium is the solvent.
In a solution, the dissolved particles are the solute.
If you filter a solution through filter paper, both the solute and the solvent pass through the filter.
Water is the universal solvent!

14. 15.2
The Solution Process
As individual solute ions break away from the crystal, the negatively and positively charged ions become surrounded by solvent molecules, and the ionic crystal dissolves. The process by which the positive and negative ions of an ionic solid become surrounded by solvent molecules is called solvation. Polar solvents such as water dissolve ionic compounds and polar compounds. Nonpolar solvents such as gasoline dissolve nonpolar compounds.
“Like dissolves like” —water is polar!

15. The Solution Process 15.2 Oil (nonpolar) and water (polar) do not mix.
Solvation of an Ionic Solid
When an ionic solid dissolves, the ions become solvated or surrounded by solvent molecules. Inferring Why do the water molecules orient themselves differently around the anions and the cations?

16. Electrolytes and Nonelectrolytes
15.2
Electrolytes and Nonelectrolytes
An electrolyte is a compound that conducts an electric current when it is in an aqueous solution or in the molten state.
All ionic compounds are electrolytes because they dissociate into ions.
The bright glow shows that sodium chloride is a strong electrolyte because nearly all the dissolved sodium chloride exists as separate Na+ and Cl– ions.

17. Electrolytes and Nonelectrolytes
15.2
Electrolytes and Nonelectrolytes
A weak electrolyte conducts electricity poorly because only a fraction of the solute in the solution exists as ions.
A compound that does not conduct an electric current in either aqueous solution or the molten state is called a nonelectrolyte.
A solution conducts electricity if it contains ions. a) Sodium chloride, a strong electrolyte, is nearly 100% dissociated into ions in water. b) Mercury(II) chloride, a weak electrolyte, is only partially dissociated in water. c) Glucose, a nonelectrolyte, does not dissociate in water.

18. A sample of blue CuSO4·5H2O is heated.
15.2
Hydrates
A compound that contains water of hydration is called a hydrate.
In writing the formula of a hydrate, use a dot to connect the formula of the compound and the number of water molecules per formula unit.
Blue crystals of CuSO4·5H2O crumble to a white anhydrous powder that has the formula CuSO4.
A sample of blue CuSO4·5H2O is heated.

19. 15.2
Hydrates
The deliquescent (removes sufficient water from the air to dissolve completely and form solutions) substance, sodium hydroxide, absorbs moisture from air.
Deliquescent substances can remove water from the air. a) Sodium hydroxide pellets absorb moisture from the air. b) Eventually a solution is formed. Applying Concepts Identify the solvent and the solute.
Example: Trial by Fire Lab

20. 15.2 Section Quiz.
1. Choose the correct words for the spaces. In any solution, the material that is dissolved is called the _______ and the material in which the substance is dissolved is called the _______ .
a) solid, liquid
b) solvent, solute
c) solute, solvent
d) crystal, disperser

21. 15.2 Section Quiz. 2. In the solution process, the
a) solvent molecules are surrounded by positive and negative ions.
b) solvent molecules become dispersed in an ionic crystal.
c) ions become emulsified in the solvent.
d) positive and negative ions are surrounded by solvent molecules.

22. 15.2 Section Quiz.
3. All ionic compounds are electrolytes because they
a) conduct electricity in the solid state.
b) dissociate into ions in the aqueous and/or the molten state.
c) remain as positive-negative pairs even when dissolved.
d) only conduct electricity in the molten state.

23. 15.2 Section Quiz. 4. The formula for iron(II) sulfate heptahydrate is
a) FeSO4(H2O)7
b) FeSO4•(H2O)7
c) Fe•2SO4•7H2O
d) FeSO4•7H2O

24. 15.3 Heterogeneous Aqueous Systems
In 1996, American astronaut Shannon Lucid shared a gelatin dessert with her Russian crewmates. Gelatin is a heterogeneous mixture called a colloid. You will learn more about the characteristics of colloids and a related mixture called a suspension.

25. Suspensions and Colloids
15.3
Suspensions and Colloids
A suspension is a mixture from which particles settle out upon standing.
A suspension differs from a solution because the particles of a suspension are much larger and do not stay suspended indefinitely.
A colloid is a heterogeneous mixture containing particles that range in size from 1 nm to 1000 nm. The particles in a colloid are spread throughout the dispersion medium.
Colloids have particles smaller than those in suspensions and larger than those in solutions.

26. Suspensions and Colloids
15.3
Suspensions and Colloids
Suspensions are heterogenous because at least two substances can be clearly identified.
Mayonnaise is heterogeneous mixture of oil and vinegar. Such a mixture would quickly separate without the presence of egg yolk, which is the emulsifying agent.

27. 15.3
Colloids
The Tyndall Effect--The scattering of visible light by colloidal particles
Particles in colloids and suspensions reflect or scatter light in all directions. Solutions do not scatter light.
The path of light is visible only when the light is scattered by particles. a) Fog or mist is a colloid and thus exhibits the Tyndall effect. b) Particles in colloids and suspensions reflect or scatter light in all directions. Solutions do not scatter light.

28. Colloids 15.3 Brownian Motion Coagulation Emulsions
The chaotic movement of colloidal particles, which was first observed by the Scottish botanist Robert Brown (1773–1858), is called Brownian motion.
Brownian motion is caused by collisions of the molecules of the dispersion medium with the small, dispersed colloidal particles.
Coagulation
A colloidal system can be destroyed, or coagulated, by the addition of ions having a charge opposite to that of the colloidal particles.
The added ions neutralize the charged colloidal particles. The particles can clump together to form heavier aggregates and precipitate from the dispersion.
Emulsions
An emulsion is a colloidal dispersion of a liquid in a liquid. An emulsifying agent is essential for the formation of an emulsion and for maintaining the emulsion’s stability.

29. 15.3
Colloids

30. 15.3 Section Quiz.
1. One characteristic that is unique to a suspension is that the particles in it
a) settle due to gravity.
b) are too small to be seen.
c) cannot be filtered.
d) produce the Tyndall effect.

31. 15.3 Section Quiz.
2. Homogenized milk contains finely divided particles that do not settle out rapidly and are not readily filtered. Thus, homogenized milk is a
a) colloid.
b) substance.
c) suspension.
d) solution.

32. 15.3 Section Quiz.
3. The scattering of light known as the Tyndall effect can be seen in
a) emulsions and solutions.
b) colloids and suspensions.
c) solutions and suspensions.
d) colloids and solutions.

33. Properties of Water Lab
Capillary Action– water moves along because it clings to itself and other things
Wikipedia: Capillary action, capillarity, capillary motion, or wicking is the ability of a substance to draw another substance into it. The standard reference is to a tube in plants but can be seen readily with porous paper. It occurs when the adhesive intermolecular forces between the liquid and a substance are stronger than the cohesive intermolecular forces inside the liquid. The effect causes a concave meniscus to form where the substance is touching a vertical surface. The same effect is what causes porous materials such as sponges to soak up liquids.
Cohesion and Adhesion—water likes to stick to itself; water likes to stick to other things

34. Water Video Human body is at least 60% water
Only 1% of water on Earth is fresh water
Water is polar (polar likes polar)
Water is the universal solvent
Chemical composition of water says it should be a gas at room temperature, but because of hydrogen bonding, water is a liquid in a wide range of conditions
Ice floats; other substances are more dense in their solid form
What else did I miss?….

35. Ch. 15--What you need to know
Water and Its Properties
Know why a water molecule is polar (bond angle 105º)
Know how and why hydrogen bonding occurs
Know properties affected by hydrogen bonding
Know surface tension (draw picture on p. 447)
Know surfactant and use
Know why water’s vapor pressure is low
Know density of water at 4ºC and at 0ºC and why ice floats
Homogeneous Aqueous Systems
Know aqueous solution
Know solute and solvent
Know that polar likes polar and non-polar likes non-polar
Know electrolyte and that all ionic compounds are electrolytes because they dissociate into ions
Know nonelectrolyte and that molecular compounds, carbon compounds, and alcohol are generally nonelectrolytes
Know hydrate
Know deliquescent compounds
Heterogeneous Aqueous Systems
Know suspension
Know colloid
From notes given in kmt/water power point
Know adhesion, cohesion, capillary action
Know six physical states (melting, vaporization, sublimation, condensation, freezing, deposition)
Know water freezes at 0ºC and boils at 100ºC
Know phase diagram