1. Campbell and Reece Chapter 3
Water & Life
Campbell and Reece
Chapter 3

2. Hydrogen Bonding 2 characteristics contribute to H-bonds
polar covalent bond between H & O
molecule is bent (V-shaped)

3. Water in Liquid State H-bonds ~ 1/20th as strong as covalent bond
bonds constantly being formed/broken (each lasts a few trillionth of a sec.)
@ any given moment a substantial % of all water molecules are part of a H-bond

4. H-bonds in Water

5. 4 Emergent Properties of Water
all 4 contribute to suitability for life on Earth
Cohesion
Moderation of Temperature by Water
Ice Floats
Water is Universal Solvent

6. Cohesion of Water Molecules
H-bonds hold water molecules together = cohesion (like molecules sticking together)
contributes (with adhesion) to the transport of water & nutrients against gravity in plants

7. Water & Nutrients Move up the Xylem

8. Surface Tension
a measure of how difficult it is to stretch or break the surface of a liquid
Water has greater surface tension than most other liquids due to H-bonding

9. Moderation of Temperature by Water
Water moderates temperature by absorbing heat from air that is warmer and releasing stored heat energy to air that is cooler.
Water can absorb or release a relatively large amount of heat with only a slight change in its own temperature.

10. Citrus Trees Sprayed with Water to Prevent Frost Damage

11. Heat & Temperature
heat: a measure of matter’s total KE due to motion of its molecules (so heat depends on volume of matter)
temperature: a measure of heat intensity; represents the average KE of its molecules regardless of volume

13. Calorie
the amt of heat it takes to raise the temperature of 1 g water 1 ºC or
the amt of heat that 1 g water releases when it cools by 1ºC

14. Kilocalories
a kilocalorie (kcal): quantity of heat required to raise temperature of 1,000 g of water by 1ºC
Food packaging calls a kcal “calorie”
1 joule (J) = cal
1 cal = J

15. Specific Heat
is the amt of heat that must be absorbed or lost for 1 g of the substance to change its temperature by 1ºC
specific heat of water is high which explains its ability to stabilize temperature

16. Specific Heat of Water 1 cal/g x ºC
specific heat of water high compared to other materials, water changes its temperature less when it absorbs or loses a given amt of heat

17. Specific Heat of Water due to H-bonding
absorbed heat must 1st break all the H-bonds b/4 it increases the average KE of its molecules
when temperature drops slightly, many additional H-bonds form  releases additional energy in form of heat

18. Water’s High Specific Heat
allows water to absorb and store a large amt of heat from Sun & warm up only a few degrees
@ night & during winter the gradually cooling water warms the air

19. Water’s High Specific Heat
the water that covers most of Earth keeps temperature fluctuations on land & water w/in limits to permit life on Earth

20. Moderating Effects of Large Bodies of Water on Temperatures

21. Evaporative Cooling temperature is average KE of molecules
some evaporization of water any temp because some individual molecules of water my gain enough KE to  gas phase

22. Heat of Vaporization
= quantity of heat a liquid must absorb for g liquid phase  gas phase
water has high heat of vaporization relative to most other liquids because of H-bonding: absorbed energy must 1st break H-bonds, then increase KE of molecules

23. High Heat of Vaporization of Water
Global scale: helps moderate Earth’s climate

24. Evaporative Cooling
= as liquid evaporates the surface of the liquid that remains cools down
contributes to stability of temperature in lakes & ponds
provides mechanism to keep terrestrial organisms from overheating

25. Evaporative Cooling

26. Ice Floats
water one of few substances that is less dense in its solid phase than in its liquid phase
water expands when goes from liquid  solid
> 4ºC water acts like other liquids: expands as it warms up, contracting as it cools

27. Ice Floats
important factor in suitability of Earth’s environment to life
if ice sank:
lakes & ponds (even oceans) could freeze solid (from bottom to top)
with summer temps only top upper meter or so would melt

28. Ice Floats
so ice insulates water below it, preventing it from freezing & allowing life to exist under frozen surface

29. Global Warming
average air temperature in Arctic has increased by 1.4ºC in the 50 years from
ice forms later in fall and melts earlier to cover smaller area

30. Water: Solvent of Life
aqueous solution: one in which water is the solvent
water is best solvent on Earth because …

31. water is polar

32. Water as Solvent
salt in water dissociates and each cation and anion is surrounded by water molecules called a hydration shell

33. Water as Solvent
sea water & cytosol in cells contain variety of ions all in hydration shells
polar molecules dissolve in water
sugars
proteins with ionic or polar regions on surface

35. Hydrophilic Substances
any substance that has an affinity for water
substances too large to dissolve but still hydrophilic  remain suspended in aqueous liquid (a colloid)

36. Hydrophobic Substances
nonionic, nonpolar substances
repel water

37. Molecular Mass/Moles sum of masses of all the atoms in a molecule
not practical to use #s of molecules so use moles (mol)
1 mole = 6.02 x 10²³

38. Molar Mass molecular mass of glucose is 144 daltons
6.02 x 10²³ daltons in 1 g
so molecular mass of glucose can be written as 144g in 1 mole of glucose
measuring in moles allows you to combine substances in fixed ratios of molecules

39. Molarity
1 mole of glucose in 1 liter water = molar or 1M solution of glucose
Molarity: the # of moles of solute per liter of water (for aqueous solutions)

41. Water on Mars
Astrobiologists have looked for life elsewhere based on: Is water present?
Mars has polar ice caps, ice under surface and enough water vapor in atmosphere to form frost
still looking for life….

43. Dissociation of Water

44. Dissociation of Water Molecules
only 1/554 million molecules of water are dissociated (in pure water)
@ 25ºC the concentration of H+ or OH-
is 10-¹ M
concentration of H+ or OH- is very low but they are each very reactive

45. pH Scale Acid a substance that increases the [H+]
overall has more H+ than OH-
Base a substance that reduces the [H+]
overall has more OH- than H+

46. pH Scale bases: 1. reduce [H+] by accepting H+ or
2. reduce [H+] indirectly by contributing OH-

47. Weak Acids Form Reversible Reactions

48. pH Scale
In any aqueous 25ºC, the product of [H+] x [OH-] = 10ˉ¹
the pH scale compresses the range of H+ and OHˉ concentrations by using logarithms
pH = the negative logarithm of [H+] or pH = -log [H+]

49. pH Scale pH < 7.0 = acid pH > 7.0 = base
most biological solutions are pH 6-8
exceptions: stomach acid is pH
Each pH unit = 10x differences in [H+] or [OHˉ] (pH of 4 has 100x more H+ than pH of 6)

50. Buffers molecules that are able to resist changes in pH
consists of an acid-base pair that combines reversibly with H+ when H+ in excess & donate H+ when they have been depleted

51. Buffers

52. Buffers

53. increases CO2 in atmosphere fresh water & sea water pH decreases
Acidification
burning fossil fuels
increases CO2 in atmosphere
CO2 dissolves in water
fresh water & sea water pH decreases

54. Acidification of Oceans

55. Acid Precipitation rain, snow, sleet, fog with a pH < 5.2
normal rain has pH 5.2
adversely affects:
life in ponds & streams
land plants
soil chemistry

56. Acid Precipitation