1. Water
Chapter 3

2. Hydrogen Bonding Water molecules are polar They have charges
Like Magnets
Charged molecules are attracted to each other
Opposites attract!
Hydrogen bond: the attraction between 2 water molecules.
Positive H to Negative O

3. Polarity of water molecules
In a water molecule, two hydrogen atoms form single polar covalent bonds with an oxygen atom.
Because oxygen is more electronegative than hydrogen, the region around the oxygen atom has a partial negative charge.
The regions near the two hydrogen atoms have a partial positive charge.
Water has a variety of unusual properties because of the attraction between polar water molecules.

5. Emergent properties of water
Cohesion and Adhesion
Surface tension
Heat Capacity
Moderation of temperature
Insulation of bodies of water
Lower density of ice compared to liquid water
Water’s ability to dissolve other substances

6. Cohesion Cohesion in Space
Hydrogen bonds hold water together, a phenomenon called cohesion
Adhesion: an attraction between molecules of different substances.
Cohesion among water molecules plays a key role in the transport of water and dissolved nutrients against gravity in plants.
Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion.
Water has a greater surface tension than most other liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface.
Water behaves as if covered by an invisible film.
Cohesion in Space

8. Temperature moderation
Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air.
Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature.
Water stabilizes temperature because it has a high specific heat.
The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C.
By definition, the specific heat of water is 1 cal per gram per degree Celsius or 1 cal/g/°C.

9. High specific heat of water
Water’s high specific heat is due to hydrogen bonding.
Heat must be absorbed to break hydrogen bonds, and heat is released when hydrogen bonds form.
Investment of one calorie of heat causes relatively little change to the temperature of water because much of the energy is used to disrupt hydrogen bonds, not speed up the movement of water molecules.

10. Water’s high heat of vaporization
Heat of vaporization is the quantity of heat that a liquid must absorb for 1 g of it to be converted from liquid to gas.
Hydrogen bonds must be broken before a water molecule can evaporate from the liquid.
Water’s high heat of vaporization moderates climate

11. Evaporative cooling
As a liquid evaporates, the surface of the liquid that remains behind cools, a phenomenon called evaporative cooling.
This occurs because the most energetic molecules are the most likely to evaporate, leaving the lower–kinetic energy molecules behind.
Evaporation of sweat in mammals or evaporation of water from the leaves of plants prevents terrestrial organisms from overheating.
Evaporative cooling moderates temperature in lakes and ponds.

12. Insulation
Water is unusual because it is less dense as a solid than as a cold liquid.
At 0°C, water becomes locked into a crystalline lattice, with each water molecule bonded to a maximum of four partners.
ice floats on the cool water below.
Water Expanding as it Freezes

13. Water is a versatile solvent
Water is an effective solvent because it readily forms hydrogen bonds with charged and polar covalent molecules.
Any substance that has an affinity for water is hydrophilic (water-loving).
These substances are dominated by ionic or polar bonds.
Substances that have no affinity for water are hydrophobic
These substances are nonionic and have nonpolar covalent bonds.

14. Polar Covalent Bonding
Electrons unequally shared between atoms
Atom that pulls on the e- more strongly  slightly negative
Atom that has a weaker pull on the e-  slightly positive
Uneven charge across the molecule  polar
Water is polar

15. Non-Polar Covalent Bonding
Electrons equally shared between atoms
No charge across the molecule  non- polar
Oils are non-polar

16. Like Dissolves Like
Polar substances dissolve in other polar substances
Ionic Compounds are polar
Example: Salt in Water
Non-polar substances dissolve in other non-polar substances
Example: Oil based paint and paint thinner
Polar and non-polar won’t mix
Example: Oil and Water

17. Like Dissolves Like Solvent Polarity Solute Ethyl acetate Non-polar
Iodine
Water
Polar
Copper (II) sulfate
Chloroform

20. Acids and Bases

21. Properties of Acids Produce H+ ions in water Taste sour Corrode metals
React with bases to form salts and water
Change pH paper red

22. Properties of Bases Produce OH- ions in water Taste bitter, chalky
Are electrolytes
Feel soapy, slippery
React with acids to form salts and water
Changes pH paper blue

23. Learning Check
Describe the solution in each of the following as: 1) acid 2) base or 3)neutral. A. ___soda B. ___soap C. ___coffee D. ___ wine E. ___ water F. ___ grapefruit

24. Solution
Describe each solution as: 1) acid 2) base or 3) neutral. A. _1_ soda B. _2_ soap C. _1_ coffee D. _1_ wine E. _3_ water F. _1_ grapefruit

25. Arrhenius Acids & Bases
Acids produce H+ in aqueous solutions
HCl  H+(aq) + Cl- (aq)
Bases produce OH- in aqueous solutions
NaOH  Na+(aq) + OH- (aq)

26. Bronsted-Lowry Acids Acids are hydrogen ion (H+) donors
Bases are hydrogen ion (H+) acceptors
HCl H2O  H3O Cl-
donor acceptor

27. Strength of Acids
determined by the concentration of [H+1] ion in the solution
greater the [H+1] is, stronger the acid is
Strong acids ionize completely, (100%) in aqueous solution
strong electrolytes
Strong Acids
HCl, HNO3 , H2SO4
Most other acids are weak.

28. Strength of Bases
Strong Bases: the bases that ionize 100% (completely) in aqueous solution
Strong Bases
NaOH, KOH, and Ca(OH)2
Most other bases are weak

29. pH Scale We use this scale to measure the strength of an acid or base.
From the French pouvoir hydrogene
“hydrogen power” or power of hydrogen
pH can use the concentration of hydronium ions or hydrogen ions.

30. 7
Acid
Base
pH Scale 14

31. pH of Common Substances

32. pH of Common Substance 14 1 x 10-14 1 x 10-0 0 13 1 x 10-13 1 x 10-1 1
pH [H1+] [OH1-] pOH
14 1 x x
13 1 x x
12 1 x x
11 1 x x
10 1 x x
9 1 x x
8 1 x x
6 1 x x
5 1 x x
4 1 x x
3 1 x x
2 1 x x
1 1 x x
0 1 x x
NaOH, 0.1 M
Household bleach
Household ammonia
Lime water
Milk of magnesia
Borax
Baking soda
Egg white, seawater
Human blood, tears
Milk
Saliva
Rain
Black coffee
Banana
Tomatoes
Wine
Cola, vinegar
Lemon juice
Gastric juice
More basic
7 1 x x
More acidic

33. Acid – Base Concentrations
10-1
pH = 3
pH = 11 H+
OH-
pH = 7
10-7
concentration (moles/L) H+
OH-
OH- H+
10-14
[H+] > [OH-]
[H+] = [OH-]
[H+] < [OH-]
acidic
solution
neutral
solution
basic
solution
Timberlake, Chemistry 7th Edition, page 332

34. pH
pH = -log [H+]

35. Neutralization Reactions
When acid and bases with equal amounts of hydrogen ion H+ and hydroxide ions OH- are mixed, the resulting solution is neutral.
NaOH (aq) + HCl(aq)  NaCl + H2O
base acid salt water
Ca(OH) HCl  CaCl H2O
base acid salt water

36. Neutralization
H+ and OH- combine to produce water H+ + OH-  H2O from acid from base neutral

37. Dissociation of water molecules
Occasionally, a hydrogen atom participating in a hydrogen bond between two water molecules shifts from one molecule to the other.
The hydrogen atom leaves its electron behind and is transferred as a single proton—a hydrogen ion (H+).
The water molecule that lost the proton is now a hydroxide ion (OH−).
The water molecule with the extra proton is now a hydronium ion (H3O+).
Hydrogen and hydroxide molecules are highly reactive
H2O  H+ + OH-

38. Acid/Base Summary

39. Acid rain Unpolluted rain has a pH of 5.6
Rain with a pH below 5.6 is “acid rain“
CO2 in the air forms carbonic acid
CO2 + H2O  H2CO3
Adds to H+ of rain
H2CO3  H+ (aq) + HCO3-(aq)

40. Sources of acid rain Power stations Oil refineries
Coal with high S content
Car and truck emissions

41. Formation of acid rain Reactions with oxygen in air form SO3
2SO2 + O2  2 SO3
Reactions with water in air form acids
SO3 + H2O  H2SO4 sulfuric acid
NO + H2O  HNO2 nitrous acid
HNO2 + H2O  HNO3 nitric acid

42. Effects of Acid rain Leaches Al from soil, which kills fish
Fish kills in spring from runoff due to accumulation of large amounts of acid in snow
Dissolves waxy coatings that protect leaves from bacteria
Corrodes metals, textiles, paper and leather