1 Water and the Fitness of the Environment chapter 3

2 H 2 O (water): The Molecule That Enables Life The biological medium The biological medium All living organisms require water All living organisms require water Cells are about 70-95% water Cells are about 70-95% water Abundance of water is the main reason Earth is habitable Abundance of water is the main reason Earth is habitable

3 Polarity hydrogen bonds  Water is polar molecule  Polarity allows formation of hydrogen bonds H O H ++ ++ –– ––

4 LE 3-2 Properties of Water  MW H 2 O = 18; MW cluster = 90 MW cluster = 90

5 Thermal Properties of Water Thermal Properties of Water Solvent Properties of Water Solvent Properties of Water Cohesion and Adhesion of Water Cohesion and Adhesion of Water Properties of water contribute to Earth’s fitness for life

6 Thermal Properties of Water  Most important -- water is liquid over the temperature range for life Melting °C Boiling °C Water (18) 0100 H 2 S (34) NH 3 (17) CO 2 (44) CH 4 (16) C 2 H 6 (30) CH 3 OH (32) C 2 H 5 OH (46)

7 Other Thermal Properties Absorption and Dissipation of Heat Absorption and Dissipation of Heat  Specific heat – amount of energy absorbed for given temperature rise (measured in J/g/°C) o Hydrogen bonds Specific Heat Water (18) 4.2 H 2 S (34) -- NH 3 (17) 5.0 CO 2 (44) -- CH 4 (16) -- C 2 H 6 (30) -- CH 3 OH (32) 2.6 C 2 H 5 OH (46) 2.4 Specific Heat Gold0.13 Silver0.23 Copper0.38 Paraffin2.5

8 Other Thermal Properties Absorption and Dissipation of Heat Absorption and Dissipation of Heat  High Thermal Conductivity  Water absorbs heat from warmer air and releases stored heat to cooler air  Water can absorb or release a large amount of heat with only a slight change in its own temperature

9 Other Thermal Properties Absorption and Dissipation of Heat Absorption and Dissipation of Heat  High Thermal Conductivity  Density of Ice

10

11 Other Thermal Properties Absorption and Dissipation of Heat Absorption and Dissipation of Heat  High Thermal Conductivity  Density of Ice  Melting and Vaporizing  Heat of fusion – amount of energy to convert 1 gram ice to 1 gram liquid water  Heat of vaporization – amount of energy to convert one mole of liquid to one mole of water vapor

12 Other Thermal Properties  Melting and Vaporizing  Heat of fusion – amount of energy to convert 1 gram ice to 1 gram liquid water (J/g)  Heat of vaporization – amount of energy to convert one mole of liquid to one mole of water vapor (J/g) o Evaporative cooling Heat of Fusion Heat of Vaporization Water (18) H 2 S (34) 70-- NH 3 (17) CO 2 (44) CH 4 (16) C 2 H 6 (30) CH 3 OH (32) C 2 H 5 OH (46)

Other Thermal Properties   Melting and Vaporizing   Heat of fusion -- melting   Heat of vaporization Heat of Fusion Heat of Vaporization Water (18) H 2 S (34) 70-- NH 3 (17) CO 2 (44) CH 4 (16) C 2 H 6 (30) CH 3 OH (32) C 2 H 5 OH (46) Heat of Fusion Heat of Vaporization Water Gold Silver Copper

14 Other Thermal Properties Absorption and Dissipation of Heat Absorption and Dissipation of Heat  Specific heat – amount of energy absorbed for given temperature rise  High Thermal Conductivity  Density of Ice  Melting and Vaporizing  Heat of fusion – amount of energy to convert 1 gram ice to 1 gram liquid water  Heat of vaporization – amount of energy to convert one mole of liquid to one mole of water vapor

15 Thermal Properties of Water Thermal Properties of Water Solvent Properties of Water Solvent Properties of Water Cohesion and Adhesion of Water Cohesion and Adhesion of Water Properties of water contribute to Earth’s fitness for life

16 Solvent Properties of Water Solution – homogeneous liquid mixture of substances Solution – homogeneous liquid mixture of substances Solvent -- dissolving agent Solvent -- dissolving agent Solute -- substance dissolved Solute -- substance dissolved Aqueous solution -- water is the solvent Aqueous solution -- water is the solvent

17 Excellent Solvent Excellent Solvent Solvent Properties of Water H O H ++ ++ –– –– H O H ++ ++ –– ––

18 Excellent Solvent Excellent Solvent Solvent Properties of Water H O H ++ ++ –– –– H O H ++ ++ –– ––  Hydration shell

LE 3-6 Na + Cl – – – – – – – – – – – –

20 Ionic Compounds Ionic Compounds Polar Compounds Polar Compounds Very large non-polar molecules if they have ionic and polar regions Very large non-polar molecules if they have ionic and polar regions Solvent Properties of Water

LE 3-7a Lysozyme molecule in a nonaqueous environment.

LE 3-7b Lysozyme molecule in a aqueous environment.

23 Hydrophilic and Hydrophobic Substances Hydrophilic – attracts water Hydrophilic – attracts water Hydrophobic – “repels” water Hydrophobic – “repels” water WATER Hydrophilic head Hydrophobic tails WATER

24 Solute Concentration in Aqueous Solutions Most biochemical reactions occur in water Most biochemical reactions occur in water Chemical reactions depend on concentration of solutes in an aqueous solution -- Moles Chemical reactions depend on concentration of solutes in an aqueous solution -- Moles One mole being 6.02 x molecules – Avogadro’s Number One mole being 6.02 x molecules – Avogadro’s Number Molarity -- moles of solute per liter of solution Molarity -- moles of solute per liter of solution

25 Thermal Properties of Water Thermal Properties of Water Solvent Properties of Water Solvent Properties of Water Cohesion and Adhesion of Water Cohesion and Adhesion of Water Properties of water contribute to Earth’s fitness for life

26 Cohesion/ Adhesion Hydrogen bonds hold water molecules together Hydrogen bonds hold water molecules together  High Surface Tension

27 Cohesion/ Adhesion Cohesion -- holds water molecules together Cohesion -- holds water molecules together  High Surface Tension  High Tensile Strength o Water 30 MPa; Copper Wire 70 MPa (yield strength)

28 Cohesion/ Adhesion Cohesion -- holds water molecules together Cohesion -- holds water molecules together Adhesion – attraction of water to solid surfaces Adhesion – attraction of water to solid surfaces Water-conducting cells 100 µm

29 Dissociation of water molecules leads to acidic and basic conditions that affect living organisms Hydronium ion (H 3 O + ) Hydroxide ion (OH – )  A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other:  The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H+)

30 Dissociation of water molecules leads to acidic and basic conditions that affect living organisms Hydronium ion (H 3 O + ) Hydroxide ion (OH – )  A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other:  Hydronium ion (H3O+) -- molecule with the extra proton;  Hydroxide ion (OH-) -- molecule that lost the proton

31 Dissociation of water molecules leads to acidic and basic conditions that affect living organisms Hydronium ion (H 3 O + ) Hydroxide ion (OH – ) H 2 O + H 2 O H 3 O + + OH - H 2 O + H 2 O H 3 O + + OH -

32 Effects of changes in pH H 2 O + H 2 O H + + H 2 O + OH - H 3 O + + OH - H 2 O + H 2 O H + + H 2 O + OH - H 3 O + + OH - H + and OH - concentrations equal in pure water H + and OH - concentrations equal in pure water pH – negative log of the concentration of hydrogen ions pH – negative log of the concentration of hydrogen ions  pH -- range 0-14 Neutral – pH = 7; Acid – pH 7 Neutral – pH = 7; Acid – pH 7  Most biologicals pH 6-8 Acids – increase H + concentration Acids – increase H + concentration Bases -- increase OH - concentration Bases -- increase OH - concentration

33 Table 2-2, p. 40

LE 3-8

35 Buffers Buffers -- minimizes changes in pH Buffers -- minimizes changes in pH Most buffers consist of an acid-base pair that reversibly combines with H + Most buffers consist of an acid-base pair that reversibly combines with H +  Donate H + in the presence of bases  Accept H + in the presence of acids

36 The Threat of Acid Precipitation Acid precipitation -- rain, snow, or fog with a pH lower than 5.6 Acid precipitation -- rain, snow, or fog with a pH lower than 5.6 Caused mainly by the mixing of different pollutants (SO 2, NO 2, CO 2 ) with water in the air Caused mainly by the mixing of different pollutants (SO 2, NO 2, CO 2 ) with water in the air

LE More basic Normal rain More acidic Acid rain

LE More basic Normal rain More acidic Acid rain FWS.gov

39