1. Water and Aqueous Systems
Chapter 15
Water and Aqueous Systems

2. Water: The Molecular View
Water is most often thought of as a (l).(liquid at room temp)
However, solid water (ice), and gaseous water (water vapor), also exist in large qty on Earth.
Water is the only sub on Earth that exists in large qty in all 3 states.

3. Modeling Water: H-Bonding
a connection between the H atoms on one molecule and a highly electro -ve atom (O, N, F) on another.
one kind of intermolecular attraction
e.g. O in water molecule and H in another water molecule.

4. H Bonding Versus Covalent Bonding in H2O
H2O molecules have both intermolecular forces (H-bonds) and
intramolecular forces (covalent bonds).
to vaporize (l) water … need heat to break H-bonds

5. Water in the Liquid State
The intermolecular attraction among water molecules results in the formn of H-bonds.

6. States of Water
H2O occurs primarily in the (l) and (s) states on Earth, rather than as a (g).
H-Bonds hold the H2O molecules together strongly enough that they cannot readily escape into the gaseous state at ordinary temperatures.

7. States of Water
That is why H2O has such a high b.p. (100° C) for such a small molecules
ethanol (C2H5OH) has a b.p. of 70°C

8. Ice Floats Ice floats in H2O.
i.e. the density of the H2O(s) < that of (l) H2O.
As H cools from 60°C, its volume decreases and its density increases.

9. Ice Floats H2O molecules move < rapidly
volume of the water decreases because the molecules pull together.
Meanwhile, the mass of H2O stays the same, so …density increases.
Below 4°C, the H2O molecules are beginning to approach the (s) state → highly organized and expand →density decreases→ float.

10. Water

11. Water Evaporation/Condensation
Vaporization
change in state of (l) to (g) (vapor)
at or above b.p. (100°C for liquid water) or
at any temperatures → evaporation
Evaporation
at surface of a (l). (molecules with enough k.e.
jump …)
at any temperature (below b.p.)

12. Evaporation/Condensation
(g) → (l)

13. Water: The Super Solvent
Most of the H2O on Earth is not pure (in solns).
because it is an excellent solvent for a variety of solutes.

14. Water: The Super Solvent
H2O is such a versatile solvent that it is sometimes called the universal solvent.

15. Solvents and Solutes aqueous solution
water that contains dissolved sub.
solvent
the dissolving medium in a soln.
exist in larger amt than solute
solute
the dissolved particles in a soln

16. Solvents and Solutes
both the solute and the solvent pass thru filter papers.

17. Solvents and Solutes A solvent dissolves the solute.
solute disperses in the solvent.
Solvents and solutes may be (g), (l), or (s).
Solute particles can be atoms, ions, or molecules.

18. The Solution Process Polar solvents e.g. water;
dissolve polar sub: most ionic cpds (e.g. NaCl), acids, bases, salts and some covalent cpds (polar covalent).
Nonpolar solvents
e.g. gasoline, alcohol, kerosene, thinner, oil, acetone (organic solvents)
dissolve nonpolar sub (e.g. grease)
Like dissolves like.

19. Electrolytes and Nonelectrolytes
a cpd that conducts an electric current when it is in an aq soln or in the molten state. (ionic cpds)
All ionic cpds (salts) are electrolytes → dissociate into ions.

20. The Solution Process Polar solvents such as water
dissolve ionic cpds and polar covalent cpds such as HCl, NH3
nonpolar solvents
such as gasoline
dissolve nonsolve nonpolar cpds (covalent) such as wax, oil,

21. Concentrated vs Dilute
Don’t use strong and weak to soln concns.
Use ‘concentrated’ and ‘dilute’ to describe concn.

22. Unsaturated vs Saturated
show soln concentration
how much solute is present relative to the max amt the soln could hold.
Unsaturated soln:
If the amt of solute dissolved is < the max that could be dissolved.
Saturated soln:
holds the max amt of solute per amt of the soln under the given conditions.

23. Solubility Solubility of a substance
The amt of a substance that can be dissolved in a given amt of solvent.
a measure of this ability for a particular substance in a particular solvent, = the qty of substance dissolving in a fixed qty of solvent to form a saturated soln under specified temperature and pressure.
in g per 100 g of solvent, moles per mole, etc

24. Unsaturated vs Saturated
Supersaturated solution
contain more solute than the usual max amt and are unstable.
cannot permanently hold the excess solute in soln and may release it suddenly.
have to be prepared carefully.
made by dissolving a solute in the soln at an elevated temp
solubility is higher than at room temp, and then
slowly cooling the soln.

25. Factors Affecting Solubiity

26. Suspensions A suspension
a mixture from which particles settle out upon standing. e.g. sand mixes with water
particles are much larger and denser--- do not stay suspended indefinitely.

27. Suspensions
Suspensions are heterogenous as at least 2 sub can be clearly identified.

28. Colloidal Systems

29. Colloids colloid a heterogeneous mixture
spread throughout the dispersion medium.
Particles smaller than those in suspensions and larger than those in solns.

30. Colloids The Tyndall Effect
The scattering of visible light by colloidal and suspension particles.

31. Colloids
Particles in colloids and suspensions reflect or scatter light in all directions. Solns do not scatter light → path of light is visible

32. Colloids Emulsions a colloidal dispersion of a (l) in a (l).
An emulsifying agent is essential for the formn of an emulsion and for maintaining the emulsion’s stability.

33. Colloids Mayonnaise is heterogeneous mixture of oil and vinegar.
quickly separate w/o the presence of egg yolk, (an emulsifying agent).
The addition of an egg yolk to a mixture of oil and vinegar produces mayonnaise, a stable emulsion.

34. Property System Solution Colloid Suspension
Particle type
Ions, atoms, small molecules
Large molecules or particles
Largest particles or aggregates
Particle size
0.1-1nm
1-1000nm
1000nm and >
Effect of light
No scattering
Exhibits Tyndall effect
Effect of gravity
Stable, does not separate
Unstable,
sediment forms
Filtration
Particles not
retained on filter
Particles not retained on filter
Particles retained on filter
Uniformity
Homogeneous
Heterogeneous

35. CST problem 2
Water is a polar solvent, while hexane is a nonpolar solvent.
Solute
Water
Hexane
NH4Cl, ammonium chloride
Soluble
insoluble
C10H8, Napththalene
Insoluble
C2H5OH, ethanol
CO(NH2)2, urea
Which of the examples above illustrates a nonpolar solute in a polar solvent?
A NH4Cl in water
B C10H8 in water
C C2H5OH in hexane
D CO(NH2)2 in hexane

36. The End