1. Water and Its Solutions
Chapter 13
Water and Its Solutions

2. 13.1 Uniquely Water Water – common substance with uncommon properties
Simple molecule – vital to life
*****Unique properties of H2O are due to three-dimensional arrangement and electron distribution

3. Water: The Molecular View
How is water different?
Substance
Formula
Molar mass
State
Melting pt
Boiling pt
Methane
CH4
16 g
gas
183
-161
Ammonia
NH3
17g
-78
-33
Water
H2O
18 g
liquid
100
Nitrogen N2
28 g
-210
-196
Oxygen O2
32 g
-218
-183
liquid at room temperature
high melting/boiling pts
solid state LESS dense then liquid state

4. Water: The Molecular View
water is a polar molecule
electrons are unequally shared
Bent structure allows a positive pole and a negative pole

5. Intermolecular Forces in Water
Water molecules are attracted to each other – opposite poles line up

6. Molecular Forces in Water
H2O molecules held together by covalent bonds (intra-molecular, solid lines)
and hydrogen bonds
(inter –molecular,
dashed lines)

7. Hydrogen Bonding the attraction of hydrogen atoms in one molecule to
an electronegative atom on another molecule

8. Water: The Hydrogen Bonding Champion
Water will form hydrogen bonds with any molecule with O – H bonds
alcohols
proteins
nucleic acids
carbohydrates

9. Water: Physical Properties Revisited
hydrogen bonds hold H2O molecules together and result in
H2O being a liquid at room temp
high boiling point

10. Ice Floats Solid H2O is less dense than liquid H2O
liquid H2O increases in density as it cools
When it hits maximum 4o C
volume begins to expand and density decreases

11. Ice Floats Why does this happen?
below 4o C water molecules begin to form an open arrangement due to hydrogen bonding
volume expands and
density decreases

12. Surface Tension
surface tension – force needed to overcome intermolecular attraction and break through the surface of a liquid
high surface tension
= high resistance
H2O has high surface
tension

13. Capillarity How does a liquid travel UP a tube?
capillarity – competition between
inter-particle attractive forces
attractive forces between the liquid and the tube

14. Water: Earth’s Thermostat
Specific heat is the amount of heat in joules needed to raise the temperature of 1 g substance 1oC.
Water has a high specific heat

15. The Dissolving Process
How does water dissolve ionic substances?
polar water molecules surround the ions
the + hydrogen pulls on the – ions
the - oxygen pulls on the + ions
this is called
dissociation

16. The Dissolving Process
How water dissolves a covalent substance:
Water forms hydrogen bonds with
the O-H group of covalent molecule
The hydrogen bond
overcomes the
intermolecular forces
of the sugar molecule

17. Like Dissolves Like
How can you predict whether a substance will dissolve in another substance?
like dissolves like
solvent and solute
must have similarities

18. Like Dissolves Like How is water like an ionic compound?
ionic compounds have charged (- & +) ions
water is polar (has partially charged ends)

19. Like Dissolves Like How is water like sugar?
both have O-H groups and form hydrogen bonds

20. Concentrated Versus Dilute
weak and strong are used to describe acids and bases
chemists use concentrated and dilute to describe solutions

21. Unsaturated Versus Saturated
unsaturated - a solution that has less than the maximum amount of solute dissolved
saturated – a solution that holds the maximum amount of dissolved solute

22. Unsaturated Versus Saturated
supersaturated – a solution that contains MORE than the maximum amount of dissolved solute --- unstable

23. Molarity molarity - # of moles of SOLUTE per liter of SOLUTION
used to determine the exact concentration of a solution
abbreviated M (= moles/liter)

24. Molarity When making a solution you need to know: the concentration
the amount of solute
total volume of solution needed
Ex: How would you prepare 5.0 L of a 0.15 M sodium chloride solution?

25. Molarity
Ex: How would you prepare 5.0 L of a 0.15 M sodium chloride solution? 5.0 L solution X 0.15 mol NaCl X 58.5 g NaCl L solution 1 mol NaCl = 43.9 g NaCl So you need to mix 43.9 g of NaCl with enough water to equal 5.0 L of solution

26. Molarity Ex: How would you prepare 2.5 L of a 0.80 M KNO3 solution?
2.5 L solution X mol KNO3 X g KNO3
L solution mol KNO3
= 202 g KNO3
So you need to mix 202 g of KNO3 with enough water to equal 2.5 L of solution