1 Water has no taste, no color, no odor; it cannot be defined, art relished while ever mysterious. Not necessary to life, but rather life itself. It fills us with a gratification that exceeds the delight of the senses.

2 Water: The Molecule That Supports All of Life

3 The following are pH values: cola– 2; orange juice– 3; apple juice– 4; coffee– 5; human blood– 7.4. Which of these liquids has the highest molar concentration of OH - ? a)cola b)orange juice c)Apple juice d)coffee e)human blood

4 Based on your knowledge of the polarity of water, the solute molecule is most likely * a)positively charged. b)negatively charged. c)neutral in charge. d)hydrophobic. e)nonpolar.

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6 Water molecules are polar Fig. 2.10

7 Hydrogen bonding in water Hydrogen bonds + + H H + +  – –  – –  – –  – –

8 Hydrogen bond formation in water A dynamic phenomenon

9 Hydrogen bonds in ice and water Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Hydrogen bond What about hydrogen bonds between molecules in water vapor?

10 Four emergent properties of water contribute to Earth’s fitness for life 1.Cohesion & adhesion 2.Moderation of temperature 3.Floating ice - insulation 4.Excellent solvent All related to hydrogen bonding

11 1. Cohesion: Water molecules stick together The hydrogen bonding of a high percentage of the molecules to neighboring molecules

12 1. Cohesion Helps pull water up through the microscopic vessels of plants Water conducting cells 100 µ m CO 2 H2OH2O O2O2 H 2 O and minerals

13 1. Cohesion Surface tension is a measure of how hard it is to break the surface of a liquid

14 1. Adhesion How does capillary action work? Fig. 2.13

15 2. Moderation of Temperature Water moderates air temperature –By absorbing heat from air that is warmer and releasing the stored heat to air that is cooler WHY?

16 2. Moderation of temperature - heat v.s. temperature Kinetic energy is energy of motion. Heat Is a measure of the total amount of kinetic energy due to molecular motion Temperature Measures the intensity of heat - not total energy

17 Which has more heat if both are the same temperture? 2. Moderation of temperature - heat v.s. temperature

18 2. Moderation of Temperature:Water’s High Specific Heat The specific heat of a substance –Is the amount of heat that must be absorbed for 1 gram of that substance to raise its temperature by 1ºC Water has a high specific heat; minimizes temperature fluctuations. Why?

19 2. Moderation of Temperature: Evaporative Cooling Heat of vaporization: the quantity of heat a liquid must absorb for 1 gram of it to be converted from a liquid to a gas Evaporative cooling Is due to water’s high heat of vaporization Allows water to cool a surface

20 3. Insulation of Bodies of Water by Floating Ice Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Hydrogen bond Why does ice float? Why is it important that ice floats?

21 4. The Solvent of Life Why is polarity important?

22 Positive hydrogen regions of water molecules cling to chloride anions (Cl – ). Figure 2.14 Water molecules Salt crystal Cl – Na + Cl – ++ ++ ++ ++ ++ –– –– –– –– –– Na + Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hydration shells Negative oxygen regions of polar water molecules are attracted to sodium cations (Na+). 4. The Solvent of Life

23 pH Dissociation of water molecules leads to acidic and basic conditions that affect living organisms

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25 Dissociation of water Water dissociates into hydronium ions and hydroxide ions H Hydronium ion (H 3 O + ) H Hydroxide ion (OH – ) H H H H H H + – + Simplified: H 2 O ↔ H + + OH - Pure water: [H + ] = M [OH - ] = M Changes in the concentration of these ions affect living organisms (note: [X] means concentration of substance X.)

26 Definition of pH The pH of a solution –Determined by relative concentration of H +

27 Acids and Bases An acid increases the hydrogen ion concentration [H + ] of a solution A base reduces the hydrogen ion concentration [H + ] of a solution

28 The logarithmic pH scale 0 pH Scale Low pH: high H +, low OH -, acid High pH: low H +, high OH -, basic Fig. 2.15

29 Things to note about pH pH scale is logarithmic: [H + ] changes 10-fold for each pH unit [H + ] x [OH - ] = –At pH 5, [H + ] = M and [OH - ] = M The internal pH of cell cytoplasm held close to pH 7

30 Buffers Buffers minimize pH changes –Absorb or release H + as necessary Fig. 2.16

31 The following are pH values: cola– 2; orange juice– 3; apple juice– 4; coffee– 5; human blood– 7.4. Which of these liquids has the highest molar concentration of OH - ? a)cola b)orange juice c)Apple juice d)coffee e)human blood

32 Based on your knowledge of the polarity of water, the solute molecule is most likely * a)positively charged. b)negatively charged. c)neutral in charge. d)hydrophobic. e)nonpolar.