1. Water and the Fitness of the Environment Chapter 3 Biology – Campbell Reece

2. Polarity of Water Because O is more electronegative than H, the e- spend more time around the O, making water a polar molecule Because O is more electronegative than H, the e- spend more time around the O, making water a polar molecule –Opposite ends of the molecule have opposite charges Water molecules are attracted to each other forming a hydrogen bond Water molecules are attracted to each other forming a hydrogen bond –The slightly positive H is attracted to the slightly negative O of another molecule

3. Figure 3.1 Hydrogen bonds between water molecules Figure 3.1 Hydrogen bonds between water molecules

4. 4 Properties of Water 1. Cohesion 2. Ability to stabilize temperature 3. Expansion upon freezing 4. Versatility as a solvent

5. Cohesion and Adhesion Cohesion – water molecules stick to each other as a result of hydrogen bonds Cohesion – water molecules stick to each other as a result of hydrogen bonds Adhesion – water molecules stick to other substances Adhesion – water molecules stick to other substances –Both aid the movement of water up a plant

6. Surface Tension Measure of how difficult it is to stretch or break the surface of a liquid Measure of how difficult it is to stretch or break the surface of a liquid

7. Temperature Stabilization Water stabilizes air temperatures by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler Water stabilizes air temperatures by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler

8. Specific Heat Water has a relatively high specific heat (the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C) Water has a relatively high specific heat (the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C) –1 cal/g/°C –Heat must be absorbed to break hydrogen bonds –Heat is released when hydrogen bonds form The large amount of water covering Earth helps keep temperature fluctuations within a livable range The large amount of water covering Earth helps keep temperature fluctuations within a livable range

9. Evaporative Cooling Molecules moving fast enough to overcome the attractions between them can depart the liquid and enter the air as gas (vaporization, or evaporation) Molecules moving fast enough to overcome the attractions between them can depart the liquid and enter the air as gas (vaporization, or evaporation) Heat of vaporization – quantity of heat a liquid must absorb for 1 g of it to be converted to a gas Heat of vaporization – quantity of heat a liquid must absorb for 1 g of it to be converted to a gas Evaporative cooling – as liquid evaporates, the surface of the liquid that remains behind cools down Evaporative cooling – as liquid evaporates, the surface of the liquid that remains behind cools down –The ‘hottest’ molecules leave first

10. Ice Floats Water is one of the few substances that are less dense as a solid than as a liquid Water is one of the few substances that are less dense as a solid than as a liquid Water expands because of hydrogen bonding Water expands because of hydrogen bonding Hydrogen bonds keep the molecules at “arms length” Hydrogen bonds keep the molecules at “arms length”

11. Figure 3.6 Floating ice and the fitness of the environment

12. Figure 3.6x2 Ice floats and frozen benzene sinks

13. Solvent of Life Solution – a liquid that is a mixture of two or more substances Solution – a liquid that is a mixture of two or more substances Solvent – the dissolving agent Solvent – the dissolving agent Solute – the substance that is dissolved Solute – the substance that is dissolved Aqueous solution – one in which water is the solvent Aqueous solution – one in which water is the solvent Water is the greatest solvent Water is the greatest solvent Ions and Polar compounds can dissolve in water Ions and Polar compounds can dissolve in water

14. Figure 3.7 A crystal of table salt dissolving in water

15. Hydrophilic vs. Hydrophobic Hydrophilic – “water loving” – a substance that has an affinity for water Hydrophilic – “water loving” – a substance that has an affinity for water –Ex. Cotton bath towel, any substance that dissolves Hydrophobic – “water fearing” – a substance that does not have an affinity for water Hydrophobic – “water fearing” – a substance that does not have an affinity for water –Ex. Vegetable oil

16. Acids and Bases Water disassociates into hydrogen (H + ) and hydroxide (OH - ) ions Water disassociates into hydrogen (H + ) and hydroxide (OH - ) ions –H 2 O ↔ H + + OH - Pure water has equal concentrations of H + and OH - Pure water has equal concentrations of H + and OH - Acid – higher concentration of H +, increases the H + concentration Acid – higher concentration of H +, increases the H + concentration Base – higher concentration of OH -, decreases the H + concentration Base – higher concentration of OH -, decreases the H + concentration

17. pH Scale [H + ][OH - ] = 10 -14 [H + ][OH - ] = 10 -14 pH = -log[H + ] pH = -log[H + ] pH of a neutral solution is 7 pH of a neutral solution is 7 Acids have a pH less than 7 Acids have a pH less than 7 Bases have a pH greater than 7 Bases have a pH greater than 7

18. Practice Problem Measurements show that the pH of a particular lake is 4.0. What is the hydrogen ion concentration of the lake? Measurements show that the pH of a particular lake is 4.0. What is the hydrogen ion concentration of the lake? 10 -4 M 10 -4 M

19. Practice Problem What is the hydroxide ion concentration of the lake described in the previous problem? What is the hydroxide ion concentration of the lake described in the previous problem? 10 -10 M 10 -10 M

20. Buffers Internal pH of most living cells close to 7 Internal pH of most living cells close to 7 –pH of human blood is 7.4 Buffers are substances that minimize changes in pH Buffers are substances that minimize changes in pH Buffers work by accepting hydrogen ions from solution when they are in excess and donating them when they are depleted Buffers work by accepting hydrogen ions from solution when they are in excess and donating them when they are depleted Carbonic acid is an important buffer Carbonic acid is an important buffer –H 2 CO 3 ↔ HCO 3 - + H +

21. Threats to Water Quality Many threats to water quality come from human activities Many threats to water quality come from human activities –Burning of fossil fuels, pollution Acid precipitation – rain, snow, or fog with a pH lower than 5.2 Acid precipitation – rain, snow, or fog with a pH lower than 5.2 –Sulfur oxides and nitrous oxides from burning fossil fuels react with water in the air –Can damage life in lakes and streams, can negatively affect soil chemistry

22. A little question for ya… Pick 2 properties of water and write a paragraph explaining their importance for living things. Pick 2 properties of water and write a paragraph explaining their importance for living things.