1. CHAPTER 9
Water and Solutions
9.1 Solutes, Solvents, and Water

2. What is a solution? Is vinegar a solution? Is milk a solution?
Is marble a solution?

3. Copper sulfate solution
A true solution is homogeneous on the molecular level
Solid copper sulfate
(CuSO4)
Copper sulfate solution
In solution the copper ions (Cu2+) dissociate from the sulfate ions (SO42–)

4. All solutions contain one solvent

5. All solutions contain one solvent and at least one solute
dissolved: term used to describe when molecules of solute are completely separated from each other and dispersed into a solution.

6. Special case of water
Most of your body is water!
Water is an important solvent with many unusual properties

7. Special case of water
Water is a small, polar molecule

8. Special case of water Water is a small, polar molecule
There is a strong attraction among water molecules due to hydrogen bonding

9. Special case of water
Hydrogen bonding leads to interesting properties in water
Substances are generally denser in the solid phase than in the liquid phase.
Water is different
Why ice floats in water

10. Special case of water
Hydrogen bonding leads to interesting properties in water
Substances are generally denser in the solid phase than in the liquid phase.
Water is different
In ice, hydrogen bonds force water molecules to align in a crystal structure where molecules are farther apart than they are in a liquid.
Why ice floats in water

11. Special case of water
Hydrogen bonding leads to interesting properties in water
Why ice floats in water

12. Why are the boiling points so different?
Special case of water
Water
H2O
18 g/mole
Methane
CH4
16 g/mole
Boils at +100oC
Boils at –161oC
Why are the boiling points so different?

13. Special case of water
Hydrogen bonding leads to interesting properties in water
Water
H2O
18 g/mole
Methane
CH4
16 g/mole
polar
nonpolar
Boils at +100oC
Boils at –161oC

14. Special case of water
Hydrogen bonding leads to interesting properties in water
Water
H2O
18 g/mole
Methane
CH4
16 g/mole
polar
nonpolar
Boils at +100oC
Boils at –161oC
Hydrogen bonds keep water molecules together, preventing them from separating easily.
Without these strong intermolecular forces, methane is a gas at room temperature

15. H-bonds keep the water molecules together
Special case of water
Why a drop of water doesn’t “lie flat” on a hard surface:
H-bonds keep the water molecules together
In reality water molecules are much, much smaller than on this drawing!
surface tension: a force acting to pull a liquid surface into the smallest possible area.

16. Special case of water
Hydrogen bonding leads to interesting properties in water
Surface tension can make a paper clip float on water

17. Dissolves many molecular compounds
Water as a solvent
Water is often called the “universal solvent”
Dissolves ionic compounds
Dissolves many molecular compounds

18. Water as a solvent Not chemically bonded
hydration: the process of molecules with any charge separation to collect water molecules around them.

19. Water as a solvent A glucose molecule has a total charge of zero,
but it has regions of positive and negative charge separation.
Not chemically bonded

20. Are there different “kinds” of water?
Distilled water
Deionized water
Tap water

21. Tap water contains dissolved salts and minerals.
Distilled water and deionized water have been
processed to remove dissolved salts and minerals.
Deionization is a specific filtration process to remove all ions.
Distillation boils water to steam which is then condensed back to liquid water

22. How do we know that tap water contains ions and
distilled water does not?
Light bulb goes off!

23. Reactions in solids
Chemical reactions in solids do occur, but they are slow
It takes thousands of years for limestone to become marble, under heat and pressure in the Earth
High density
Low mobility

24. Reactions in gases
Chemical reactions in gases do occur, and happen quickly
Low density
High mobility

25. Reactions in liquids Chemical reactions in liquids occur easily
High density
High mobility
Chemical reactions in liquids occur easily

26. Reactions in liquids
Life involves many complex chemical reactions that only occur in aqueous solutions!
A step in the Krebs cycle – this is how energy is extracted from glucose

27. Not everything dissolves in water. Why not?

28. Not everything dissolves in water. Why not?
In general,
“like” dissolves “like”
Polar solvents dissolve polar solutes
Nonpolar solvents dissolve nonpolar solutes

29. Polar solvents dissolve polar solutes
Hexane can dissolve oil paints because both are nonpolar.
In general,
“like” dissolves “like”
Polar solvents dissolve polar solutes
Nonpolar solvents dissolve nonpolar solutes

30. Water is often called the “universal solvent”:
Dissolving ionic salts
Dissolving molecular compounds
In general,
“like” dissolves “like”
Polar solvents dissolve polar solutes
Nonpolar solvents dissolve nonpolar solutes